mm: speed up cancel_dirty_page() for clean pages
[sfrench/cifs-2.6.git] / mm / page-writeback.c
1 /*
2  * mm/page-writeback.c
3  *
4  * Copyright (C) 2002, Linus Torvalds.
5  * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
6  *
7  * Contains functions related to writing back dirty pages at the
8  * address_space level.
9  *
10  * 10Apr2002    Andrew Morton
11  *              Initial version
12  */
13
14 #include <linux/kernel.h>
15 #include <linux/export.h>
16 #include <linux/spinlock.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 #include <linux/swap.h>
20 #include <linux/slab.h>
21 #include <linux/pagemap.h>
22 #include <linux/writeback.h>
23 #include <linux/init.h>
24 #include <linux/backing-dev.h>
25 #include <linux/task_io_accounting_ops.h>
26 #include <linux/blkdev.h>
27 #include <linux/mpage.h>
28 #include <linux/rmap.h>
29 #include <linux/percpu.h>
30 #include <linux/notifier.h>
31 #include <linux/smp.h>
32 #include <linux/sysctl.h>
33 #include <linux/cpu.h>
34 #include <linux/syscalls.h>
35 #include <linux/buffer_head.h> /* __set_page_dirty_buffers */
36 #include <linux/pagevec.h>
37 #include <linux/timer.h>
38 #include <linux/sched/rt.h>
39 #include <linux/sched/signal.h>
40 #include <linux/mm_inline.h>
41 #include <trace/events/writeback.h>
42
43 #include "internal.h"
44
45 /*
46  * Sleep at most 200ms at a time in balance_dirty_pages().
47  */
48 #define MAX_PAUSE               max(HZ/5, 1)
49
50 /*
51  * Try to keep balance_dirty_pages() call intervals higher than this many pages
52  * by raising pause time to max_pause when falls below it.
53  */
54 #define DIRTY_POLL_THRESH       (128 >> (PAGE_SHIFT - 10))
55
56 /*
57  * Estimate write bandwidth at 200ms intervals.
58  */
59 #define BANDWIDTH_INTERVAL      max(HZ/5, 1)
60
61 #define RATELIMIT_CALC_SHIFT    10
62
63 /*
64  * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
65  * will look to see if it needs to force writeback or throttling.
66  */
67 static long ratelimit_pages = 32;
68
69 /* The following parameters are exported via /proc/sys/vm */
70
71 /*
72  * Start background writeback (via writeback threads) at this percentage
73  */
74 int dirty_background_ratio = 10;
75
76 /*
77  * dirty_background_bytes starts at 0 (disabled) so that it is a function of
78  * dirty_background_ratio * the amount of dirtyable memory
79  */
80 unsigned long dirty_background_bytes;
81
82 /*
83  * free highmem will not be subtracted from the total free memory
84  * for calculating free ratios if vm_highmem_is_dirtyable is true
85  */
86 int vm_highmem_is_dirtyable;
87
88 /*
89  * The generator of dirty data starts writeback at this percentage
90  */
91 int vm_dirty_ratio = 20;
92
93 /*
94  * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
95  * vm_dirty_ratio * the amount of dirtyable memory
96  */
97 unsigned long vm_dirty_bytes;
98
99 /*
100  * The interval between `kupdate'-style writebacks
101  */
102 unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */
103
104 EXPORT_SYMBOL_GPL(dirty_writeback_interval);
105
106 /*
107  * The longest time for which data is allowed to remain dirty
108  */
109 unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */
110
111 /*
112  * Flag that makes the machine dump writes/reads and block dirtyings.
113  */
114 int block_dump;
115
116 /*
117  * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
118  * a full sync is triggered after this time elapses without any disk activity.
119  */
120 int laptop_mode;
121
122 EXPORT_SYMBOL(laptop_mode);
123
124 /* End of sysctl-exported parameters */
125
126 struct wb_domain global_wb_domain;
127
128 /* consolidated parameters for balance_dirty_pages() and its subroutines */
129 struct dirty_throttle_control {
130 #ifdef CONFIG_CGROUP_WRITEBACK
131         struct wb_domain        *dom;
132         struct dirty_throttle_control *gdtc;    /* only set in memcg dtc's */
133 #endif
134         struct bdi_writeback    *wb;
135         struct fprop_local_percpu *wb_completions;
136
137         unsigned long           avail;          /* dirtyable */
138         unsigned long           dirty;          /* file_dirty + write + nfs */
139         unsigned long           thresh;         /* dirty threshold */
140         unsigned long           bg_thresh;      /* dirty background threshold */
141
142         unsigned long           wb_dirty;       /* per-wb counterparts */
143         unsigned long           wb_thresh;
144         unsigned long           wb_bg_thresh;
145
146         unsigned long           pos_ratio;
147 };
148
149 /*
150  * Length of period for aging writeout fractions of bdis. This is an
151  * arbitrarily chosen number. The longer the period, the slower fractions will
152  * reflect changes in current writeout rate.
153  */
154 #define VM_COMPLETIONS_PERIOD_LEN (3*HZ)
155
156 #ifdef CONFIG_CGROUP_WRITEBACK
157
158 #define GDTC_INIT(__wb)         .wb = (__wb),                           \
159                                 .dom = &global_wb_domain,               \
160                                 .wb_completions = &(__wb)->completions
161
162 #define GDTC_INIT_NO_WB         .dom = &global_wb_domain
163
164 #define MDTC_INIT(__wb, __gdtc) .wb = (__wb),                           \
165                                 .dom = mem_cgroup_wb_domain(__wb),      \
166                                 .wb_completions = &(__wb)->memcg_completions, \
167                                 .gdtc = __gdtc
168
169 static bool mdtc_valid(struct dirty_throttle_control *dtc)
170 {
171         return dtc->dom;
172 }
173
174 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
175 {
176         return dtc->dom;
177 }
178
179 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
180 {
181         return mdtc->gdtc;
182 }
183
184 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
185 {
186         return &wb->memcg_completions;
187 }
188
189 static void wb_min_max_ratio(struct bdi_writeback *wb,
190                              unsigned long *minp, unsigned long *maxp)
191 {
192         unsigned long this_bw = wb->avg_write_bandwidth;
193         unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
194         unsigned long long min = wb->bdi->min_ratio;
195         unsigned long long max = wb->bdi->max_ratio;
196
197         /*
198          * @wb may already be clean by the time control reaches here and
199          * the total may not include its bw.
200          */
201         if (this_bw < tot_bw) {
202                 if (min) {
203                         min *= this_bw;
204                         do_div(min, tot_bw);
205                 }
206                 if (max < 100) {
207                         max *= this_bw;
208                         do_div(max, tot_bw);
209                 }
210         }
211
212         *minp = min;
213         *maxp = max;
214 }
215
216 #else   /* CONFIG_CGROUP_WRITEBACK */
217
218 #define GDTC_INIT(__wb)         .wb = (__wb),                           \
219                                 .wb_completions = &(__wb)->completions
220 #define GDTC_INIT_NO_WB
221 #define MDTC_INIT(__wb, __gdtc)
222
223 static bool mdtc_valid(struct dirty_throttle_control *dtc)
224 {
225         return false;
226 }
227
228 static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
229 {
230         return &global_wb_domain;
231 }
232
233 static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
234 {
235         return NULL;
236 }
237
238 static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
239 {
240         return NULL;
241 }
242
243 static void wb_min_max_ratio(struct bdi_writeback *wb,
244                              unsigned long *minp, unsigned long *maxp)
245 {
246         *minp = wb->bdi->min_ratio;
247         *maxp = wb->bdi->max_ratio;
248 }
249
250 #endif  /* CONFIG_CGROUP_WRITEBACK */
251
252 /*
253  * In a memory zone, there is a certain amount of pages we consider
254  * available for the page cache, which is essentially the number of
255  * free and reclaimable pages, minus some zone reserves to protect
256  * lowmem and the ability to uphold the zone's watermarks without
257  * requiring writeback.
258  *
259  * This number of dirtyable pages is the base value of which the
260  * user-configurable dirty ratio is the effictive number of pages that
261  * are allowed to be actually dirtied.  Per individual zone, or
262  * globally by using the sum of dirtyable pages over all zones.
263  *
264  * Because the user is allowed to specify the dirty limit globally as
265  * absolute number of bytes, calculating the per-zone dirty limit can
266  * require translating the configured limit into a percentage of
267  * global dirtyable memory first.
268  */
269
270 /**
271  * node_dirtyable_memory - number of dirtyable pages in a node
272  * @pgdat: the node
273  *
274  * Returns the node's number of pages potentially available for dirty
275  * page cache.  This is the base value for the per-node dirty limits.
276  */
277 static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
278 {
279         unsigned long nr_pages = 0;
280         int z;
281
282         for (z = 0; z < MAX_NR_ZONES; z++) {
283                 struct zone *zone = pgdat->node_zones + z;
284
285                 if (!populated_zone(zone))
286                         continue;
287
288                 nr_pages += zone_page_state(zone, NR_FREE_PAGES);
289         }
290
291         /*
292          * Pages reserved for the kernel should not be considered
293          * dirtyable, to prevent a situation where reclaim has to
294          * clean pages in order to balance the zones.
295          */
296         nr_pages -= min(nr_pages, pgdat->totalreserve_pages);
297
298         nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
299         nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);
300
301         return nr_pages;
302 }
303
304 static unsigned long highmem_dirtyable_memory(unsigned long total)
305 {
306 #ifdef CONFIG_HIGHMEM
307         int node;
308         unsigned long x = 0;
309         int i;
310
311         for_each_node_state(node, N_HIGH_MEMORY) {
312                 for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
313                         struct zone *z;
314                         unsigned long nr_pages;
315
316                         if (!is_highmem_idx(i))
317                                 continue;
318
319                         z = &NODE_DATA(node)->node_zones[i];
320                         if (!populated_zone(z))
321                                 continue;
322
323                         nr_pages = zone_page_state(z, NR_FREE_PAGES);
324                         /* watch for underflows */
325                         nr_pages -= min(nr_pages, high_wmark_pages(z));
326                         nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
327                         nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
328                         x += nr_pages;
329                 }
330         }
331
332         /*
333          * Unreclaimable memory (kernel memory or anonymous memory
334          * without swap) can bring down the dirtyable pages below
335          * the zone's dirty balance reserve and the above calculation
336          * will underflow.  However we still want to add in nodes
337          * which are below threshold (negative values) to get a more
338          * accurate calculation but make sure that the total never
339          * underflows.
340          */
341         if ((long)x < 0)
342                 x = 0;
343
344         /*
345          * Make sure that the number of highmem pages is never larger
346          * than the number of the total dirtyable memory. This can only
347          * occur in very strange VM situations but we want to make sure
348          * that this does not occur.
349          */
350         return min(x, total);
351 #else
352         return 0;
353 #endif
354 }
355
356 /**
357  * global_dirtyable_memory - number of globally dirtyable pages
358  *
359  * Returns the global number of pages potentially available for dirty
360  * page cache.  This is the base value for the global dirty limits.
361  */
362 static unsigned long global_dirtyable_memory(void)
363 {
364         unsigned long x;
365
366         x = global_zone_page_state(NR_FREE_PAGES);
367         /*
368          * Pages reserved for the kernel should not be considered
369          * dirtyable, to prevent a situation where reclaim has to
370          * clean pages in order to balance the zones.
371          */
372         x -= min(x, totalreserve_pages);
373
374         x += global_node_page_state(NR_INACTIVE_FILE);
375         x += global_node_page_state(NR_ACTIVE_FILE);
376
377         if (!vm_highmem_is_dirtyable)
378                 x -= highmem_dirtyable_memory(x);
379
380         return x + 1;   /* Ensure that we never return 0 */
381 }
382
383 /**
384  * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
385  * @dtc: dirty_throttle_control of interest
386  *
387  * Calculate @dtc->thresh and ->bg_thresh considering
388  * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}.  The caller
389  * must ensure that @dtc->avail is set before calling this function.  The
390  * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and
391  * real-time tasks.
392  */
393 static void domain_dirty_limits(struct dirty_throttle_control *dtc)
394 {
395         const unsigned long available_memory = dtc->avail;
396         struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
397         unsigned long bytes = vm_dirty_bytes;
398         unsigned long bg_bytes = dirty_background_bytes;
399         /* convert ratios to per-PAGE_SIZE for higher precision */
400         unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
401         unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
402         unsigned long thresh;
403         unsigned long bg_thresh;
404         struct task_struct *tsk;
405
406         /* gdtc is !NULL iff @dtc is for memcg domain */
407         if (gdtc) {
408                 unsigned long global_avail = gdtc->avail;
409
410                 /*
411                  * The byte settings can't be applied directly to memcg
412                  * domains.  Convert them to ratios by scaling against
413                  * globally available memory.  As the ratios are in
414                  * per-PAGE_SIZE, they can be obtained by dividing bytes by
415                  * number of pages.
416                  */
417                 if (bytes)
418                         ratio = min(DIV_ROUND_UP(bytes, global_avail),
419                                     PAGE_SIZE);
420                 if (bg_bytes)
421                         bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
422                                        PAGE_SIZE);
423                 bytes = bg_bytes = 0;
424         }
425
426         if (bytes)
427                 thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
428         else
429                 thresh = (ratio * available_memory) / PAGE_SIZE;
430
431         if (bg_bytes)
432                 bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
433         else
434                 bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
435
436         if (unlikely(bg_thresh >= thresh)) {
437                 pr_warn("vm direct limit must be set greater than background limit.\n");
438                 bg_thresh = thresh / 2;
439         }
440
441         tsk = current;
442         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
443                 bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
444                 thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
445         }
446         dtc->thresh = thresh;
447         dtc->bg_thresh = bg_thresh;
448
449         /* we should eventually report the domain in the TP */
450         if (!gdtc)
451                 trace_global_dirty_state(bg_thresh, thresh);
452 }
453
454 /**
455  * global_dirty_limits - background-writeback and dirty-throttling thresholds
456  * @pbackground: out parameter for bg_thresh
457  * @pdirty: out parameter for thresh
458  *
459  * Calculate bg_thresh and thresh for global_wb_domain.  See
460  * domain_dirty_limits() for details.
461  */
462 void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
463 {
464         struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
465
466         gdtc.avail = global_dirtyable_memory();
467         domain_dirty_limits(&gdtc);
468
469         *pbackground = gdtc.bg_thresh;
470         *pdirty = gdtc.thresh;
471 }
472
473 /**
474  * node_dirty_limit - maximum number of dirty pages allowed in a node
475  * @pgdat: the node
476  *
477  * Returns the maximum number of dirty pages allowed in a node, based
478  * on the node's dirtyable memory.
479  */
480 static unsigned long node_dirty_limit(struct pglist_data *pgdat)
481 {
482         unsigned long node_memory = node_dirtyable_memory(pgdat);
483         struct task_struct *tsk = current;
484         unsigned long dirty;
485
486         if (vm_dirty_bytes)
487                 dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
488                         node_memory / global_dirtyable_memory();
489         else
490                 dirty = vm_dirty_ratio * node_memory / 100;
491
492         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
493                 dirty += dirty / 4;
494
495         return dirty;
496 }
497
498 /**
499  * node_dirty_ok - tells whether a node is within its dirty limits
500  * @pgdat: the node to check
501  *
502  * Returns %true when the dirty pages in @pgdat are within the node's
503  * dirty limit, %false if the limit is exceeded.
504  */
505 bool node_dirty_ok(struct pglist_data *pgdat)
506 {
507         unsigned long limit = node_dirty_limit(pgdat);
508         unsigned long nr_pages = 0;
509
510         nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
511         nr_pages += node_page_state(pgdat, NR_UNSTABLE_NFS);
512         nr_pages += node_page_state(pgdat, NR_WRITEBACK);
513
514         return nr_pages <= limit;
515 }
516
517 int dirty_background_ratio_handler(struct ctl_table *table, int write,
518                 void __user *buffer, size_t *lenp,
519                 loff_t *ppos)
520 {
521         int ret;
522
523         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
524         if (ret == 0 && write)
525                 dirty_background_bytes = 0;
526         return ret;
527 }
528
529 int dirty_background_bytes_handler(struct ctl_table *table, int write,
530                 void __user *buffer, size_t *lenp,
531                 loff_t *ppos)
532 {
533         int ret;
534
535         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
536         if (ret == 0 && write)
537                 dirty_background_ratio = 0;
538         return ret;
539 }
540
541 int dirty_ratio_handler(struct ctl_table *table, int write,
542                 void __user *buffer, size_t *lenp,
543                 loff_t *ppos)
544 {
545         int old_ratio = vm_dirty_ratio;
546         int ret;
547
548         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
549         if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
550                 writeback_set_ratelimit();
551                 vm_dirty_bytes = 0;
552         }
553         return ret;
554 }
555
556 int dirty_bytes_handler(struct ctl_table *table, int write,
557                 void __user *buffer, size_t *lenp,
558                 loff_t *ppos)
559 {
560         unsigned long old_bytes = vm_dirty_bytes;
561         int ret;
562
563         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
564         if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
565                 writeback_set_ratelimit();
566                 vm_dirty_ratio = 0;
567         }
568         return ret;
569 }
570
571 static unsigned long wp_next_time(unsigned long cur_time)
572 {
573         cur_time += VM_COMPLETIONS_PERIOD_LEN;
574         /* 0 has a special meaning... */
575         if (!cur_time)
576                 return 1;
577         return cur_time;
578 }
579
580 static void wb_domain_writeout_inc(struct wb_domain *dom,
581                                    struct fprop_local_percpu *completions,
582                                    unsigned int max_prop_frac)
583 {
584         __fprop_inc_percpu_max(&dom->completions, completions,
585                                max_prop_frac);
586         /* First event after period switching was turned off? */
587         if (unlikely(!dom->period_time)) {
588                 /*
589                  * We can race with other __bdi_writeout_inc calls here but
590                  * it does not cause any harm since the resulting time when
591                  * timer will fire and what is in writeout_period_time will be
592                  * roughly the same.
593                  */
594                 dom->period_time = wp_next_time(jiffies);
595                 mod_timer(&dom->period_timer, dom->period_time);
596         }
597 }
598
599 /*
600  * Increment @wb's writeout completion count and the global writeout
601  * completion count. Called from test_clear_page_writeback().
602  */
603 static inline void __wb_writeout_inc(struct bdi_writeback *wb)
604 {
605         struct wb_domain *cgdom;
606
607         inc_wb_stat(wb, WB_WRITTEN);
608         wb_domain_writeout_inc(&global_wb_domain, &wb->completions,
609                                wb->bdi->max_prop_frac);
610
611         cgdom = mem_cgroup_wb_domain(wb);
612         if (cgdom)
613                 wb_domain_writeout_inc(cgdom, wb_memcg_completions(wb),
614                                        wb->bdi->max_prop_frac);
615 }
616
617 void wb_writeout_inc(struct bdi_writeback *wb)
618 {
619         unsigned long flags;
620
621         local_irq_save(flags);
622         __wb_writeout_inc(wb);
623         local_irq_restore(flags);
624 }
625 EXPORT_SYMBOL_GPL(wb_writeout_inc);
626
627 /*
628  * On idle system, we can be called long after we scheduled because we use
629  * deferred timers so count with missed periods.
630  */
631 static void writeout_period(struct timer_list *t)
632 {
633         struct wb_domain *dom = from_timer(dom, t, period_timer);
634         int miss_periods = (jiffies - dom->period_time) /
635                                                  VM_COMPLETIONS_PERIOD_LEN;
636
637         if (fprop_new_period(&dom->completions, miss_periods + 1)) {
638                 dom->period_time = wp_next_time(dom->period_time +
639                                 miss_periods * VM_COMPLETIONS_PERIOD_LEN);
640                 mod_timer(&dom->period_timer, dom->period_time);
641         } else {
642                 /*
643                  * Aging has zeroed all fractions. Stop wasting CPU on period
644                  * updates.
645                  */
646                 dom->period_time = 0;
647         }
648 }
649
650 int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
651 {
652         memset(dom, 0, sizeof(*dom));
653
654         spin_lock_init(&dom->lock);
655
656         timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);
657
658         dom->dirty_limit_tstamp = jiffies;
659
660         return fprop_global_init(&dom->completions, gfp);
661 }
662
663 #ifdef CONFIG_CGROUP_WRITEBACK
664 void wb_domain_exit(struct wb_domain *dom)
665 {
666         del_timer_sync(&dom->period_timer);
667         fprop_global_destroy(&dom->completions);
668 }
669 #endif
670
671 /*
672  * bdi_min_ratio keeps the sum of the minimum dirty shares of all
673  * registered backing devices, which, for obvious reasons, can not
674  * exceed 100%.
675  */
676 static unsigned int bdi_min_ratio;
677
678 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
679 {
680         int ret = 0;
681
682         spin_lock_bh(&bdi_lock);
683         if (min_ratio > bdi->max_ratio) {
684                 ret = -EINVAL;
685         } else {
686                 min_ratio -= bdi->min_ratio;
687                 if (bdi_min_ratio + min_ratio < 100) {
688                         bdi_min_ratio += min_ratio;
689                         bdi->min_ratio += min_ratio;
690                 } else {
691                         ret = -EINVAL;
692                 }
693         }
694         spin_unlock_bh(&bdi_lock);
695
696         return ret;
697 }
698
699 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
700 {
701         int ret = 0;
702
703         if (max_ratio > 100)
704                 return -EINVAL;
705
706         spin_lock_bh(&bdi_lock);
707         if (bdi->min_ratio > max_ratio) {
708                 ret = -EINVAL;
709         } else {
710                 bdi->max_ratio = max_ratio;
711                 bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
712         }
713         spin_unlock_bh(&bdi_lock);
714
715         return ret;
716 }
717 EXPORT_SYMBOL(bdi_set_max_ratio);
718
719 static unsigned long dirty_freerun_ceiling(unsigned long thresh,
720                                            unsigned long bg_thresh)
721 {
722         return (thresh + bg_thresh) / 2;
723 }
724
725 static unsigned long hard_dirty_limit(struct wb_domain *dom,
726                                       unsigned long thresh)
727 {
728         return max(thresh, dom->dirty_limit);
729 }
730
731 /*
732  * Memory which can be further allocated to a memcg domain is capped by
733  * system-wide clean memory excluding the amount being used in the domain.
734  */
735 static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
736                             unsigned long filepages, unsigned long headroom)
737 {
738         struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
739         unsigned long clean = filepages - min(filepages, mdtc->dirty);
740         unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
741         unsigned long other_clean = global_clean - min(global_clean, clean);
742
743         mdtc->avail = filepages + min(headroom, other_clean);
744 }
745
746 /**
747  * __wb_calc_thresh - @wb's share of dirty throttling threshold
748  * @dtc: dirty_throttle_context of interest
749  *
750  * Returns @wb's dirty limit in pages. The term "dirty" in the context of
751  * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
752  *
753  * Note that balance_dirty_pages() will only seriously take it as a hard limit
754  * when sleeping max_pause per page is not enough to keep the dirty pages under
755  * control. For example, when the device is completely stalled due to some error
756  * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
757  * In the other normal situations, it acts more gently by throttling the tasks
758  * more (rather than completely block them) when the wb dirty pages go high.
759  *
760  * It allocates high/low dirty limits to fast/slow devices, in order to prevent
761  * - starving fast devices
762  * - piling up dirty pages (that will take long time to sync) on slow devices
763  *
764  * The wb's share of dirty limit will be adapting to its throughput and
765  * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
766  */
767 static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
768 {
769         struct wb_domain *dom = dtc_dom(dtc);
770         unsigned long thresh = dtc->thresh;
771         u64 wb_thresh;
772         long numerator, denominator;
773         unsigned long wb_min_ratio, wb_max_ratio;
774
775         /*
776          * Calculate this BDI's share of the thresh ratio.
777          */
778         fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
779                               &numerator, &denominator);
780
781         wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
782         wb_thresh *= numerator;
783         do_div(wb_thresh, denominator);
784
785         wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
786
787         wb_thresh += (thresh * wb_min_ratio) / 100;
788         if (wb_thresh > (thresh * wb_max_ratio) / 100)
789                 wb_thresh = thresh * wb_max_ratio / 100;
790
791         return wb_thresh;
792 }
793
794 unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
795 {
796         struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
797                                                .thresh = thresh };
798         return __wb_calc_thresh(&gdtc);
799 }
800
801 /*
802  *                           setpoint - dirty 3
803  *        f(dirty) := 1.0 + (----------------)
804  *                           limit - setpoint
805  *
806  * it's a 3rd order polynomial that subjects to
807  *
808  * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
809  * (2) f(setpoint) = 1.0 => the balance point
810  * (3) f(limit)    = 0   => the hard limit
811  * (4) df/dx      <= 0   => negative feedback control
812  * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
813  *     => fast response on large errors; small oscillation near setpoint
814  */
815 static long long pos_ratio_polynom(unsigned long setpoint,
816                                           unsigned long dirty,
817                                           unsigned long limit)
818 {
819         long long pos_ratio;
820         long x;
821
822         x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
823                       (limit - setpoint) | 1);
824         pos_ratio = x;
825         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
826         pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
827         pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
828
829         return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
830 }
831
832 /*
833  * Dirty position control.
834  *
835  * (o) global/bdi setpoints
836  *
837  * We want the dirty pages be balanced around the global/wb setpoints.
838  * When the number of dirty pages is higher/lower than the setpoint, the
839  * dirty position control ratio (and hence task dirty ratelimit) will be
840  * decreased/increased to bring the dirty pages back to the setpoint.
841  *
842  *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
843  *
844  *     if (dirty < setpoint) scale up   pos_ratio
845  *     if (dirty > setpoint) scale down pos_ratio
846  *
847  *     if (wb_dirty < wb_setpoint) scale up   pos_ratio
848  *     if (wb_dirty > wb_setpoint) scale down pos_ratio
849  *
850  *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
851  *
852  * (o) global control line
853  *
854  *     ^ pos_ratio
855  *     |
856  *     |            |<===== global dirty control scope ======>|
857  * 2.0 .............*
858  *     |            .*
859  *     |            . *
860  *     |            .   *
861  *     |            .     *
862  *     |            .        *
863  *     |            .            *
864  * 1.0 ................................*
865  *     |            .                  .     *
866  *     |            .                  .          *
867  *     |            .                  .              *
868  *     |            .                  .                 *
869  *     |            .                  .                    *
870  *   0 +------------.------------------.----------------------*------------->
871  *           freerun^          setpoint^                 limit^   dirty pages
872  *
873  * (o) wb control line
874  *
875  *     ^ pos_ratio
876  *     |
877  *     |            *
878  *     |              *
879  *     |                *
880  *     |                  *
881  *     |                    * |<=========== span ============>|
882  * 1.0 .......................*
883  *     |                      . *
884  *     |                      .   *
885  *     |                      .     *
886  *     |                      .       *
887  *     |                      .         *
888  *     |                      .           *
889  *     |                      .             *
890  *     |                      .               *
891  *     |                      .                 *
892  *     |                      .                   *
893  *     |                      .                     *
894  * 1/4 ...............................................* * * * * * * * * * * *
895  *     |                      .                         .
896  *     |                      .                           .
897  *     |                      .                             .
898  *   0 +----------------------.-------------------------------.------------->
899  *                wb_setpoint^                    x_intercept^
900  *
901  * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
902  * be smoothly throttled down to normal if it starts high in situations like
903  * - start writing to a slow SD card and a fast disk at the same time. The SD
904  *   card's wb_dirty may rush to many times higher than wb_setpoint.
905  * - the wb dirty thresh drops quickly due to change of JBOD workload
906  */
907 static void wb_position_ratio(struct dirty_throttle_control *dtc)
908 {
909         struct bdi_writeback *wb = dtc->wb;
910         unsigned long write_bw = wb->avg_write_bandwidth;
911         unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
912         unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
913         unsigned long wb_thresh = dtc->wb_thresh;
914         unsigned long x_intercept;
915         unsigned long setpoint;         /* dirty pages' target balance point */
916         unsigned long wb_setpoint;
917         unsigned long span;
918         long long pos_ratio;            /* for scaling up/down the rate limit */
919         long x;
920
921         dtc->pos_ratio = 0;
922
923         if (unlikely(dtc->dirty >= limit))
924                 return;
925
926         /*
927          * global setpoint
928          *
929          * See comment for pos_ratio_polynom().
930          */
931         setpoint = (freerun + limit) / 2;
932         pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);
933
934         /*
935          * The strictlimit feature is a tool preventing mistrusted filesystems
936          * from growing a large number of dirty pages before throttling. For
937          * such filesystems balance_dirty_pages always checks wb counters
938          * against wb limits. Even if global "nr_dirty" is under "freerun".
939          * This is especially important for fuse which sets bdi->max_ratio to
940          * 1% by default. Without strictlimit feature, fuse writeback may
941          * consume arbitrary amount of RAM because it is accounted in
942          * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
943          *
944          * Here, in wb_position_ratio(), we calculate pos_ratio based on
945          * two values: wb_dirty and wb_thresh. Let's consider an example:
946          * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
947          * limits are set by default to 10% and 20% (background and throttle).
948          * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
949          * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
950          * about ~6K pages (as the average of background and throttle wb
951          * limits). The 3rd order polynomial will provide positive feedback if
952          * wb_dirty is under wb_setpoint and vice versa.
953          *
954          * Note, that we cannot use global counters in these calculations
955          * because we want to throttle process writing to a strictlimit wb
956          * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
957          * in the example above).
958          */
959         if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
960                 long long wb_pos_ratio;
961
962                 if (dtc->wb_dirty < 8) {
963                         dtc->pos_ratio = min_t(long long, pos_ratio * 2,
964                                            2 << RATELIMIT_CALC_SHIFT);
965                         return;
966                 }
967
968                 if (dtc->wb_dirty >= wb_thresh)
969                         return;
970
971                 wb_setpoint = dirty_freerun_ceiling(wb_thresh,
972                                                     dtc->wb_bg_thresh);
973
974                 if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
975                         return;
976
977                 wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
978                                                  wb_thresh);
979
980                 /*
981                  * Typically, for strictlimit case, wb_setpoint << setpoint
982                  * and pos_ratio >> wb_pos_ratio. In the other words global
983                  * state ("dirty") is not limiting factor and we have to
984                  * make decision based on wb counters. But there is an
985                  * important case when global pos_ratio should get precedence:
986                  * global limits are exceeded (e.g. due to activities on other
987                  * wb's) while given strictlimit wb is below limit.
988                  *
989                  * "pos_ratio * wb_pos_ratio" would work for the case above,
990                  * but it would look too non-natural for the case of all
991                  * activity in the system coming from a single strictlimit wb
992                  * with bdi->max_ratio == 100%.
993                  *
994                  * Note that min() below somewhat changes the dynamics of the
995                  * control system. Normally, pos_ratio value can be well over 3
996                  * (when globally we are at freerun and wb is well below wb
997                  * setpoint). Now the maximum pos_ratio in the same situation
998                  * is 2. We might want to tweak this if we observe the control
999                  * system is too slow to adapt.
1000                  */
1001                 dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
1002                 return;
1003         }
1004
1005         /*
1006          * We have computed basic pos_ratio above based on global situation. If
1007          * the wb is over/under its share of dirty pages, we want to scale
1008          * pos_ratio further down/up. That is done by the following mechanism.
1009          */
1010
1011         /*
1012          * wb setpoint
1013          *
1014          *        f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
1015          *
1016          *                        x_intercept - wb_dirty
1017          *                     := --------------------------
1018          *                        x_intercept - wb_setpoint
1019          *
1020          * The main wb control line is a linear function that subjects to
1021          *
1022          * (1) f(wb_setpoint) = 1.0
1023          * (2) k = - 1 / (8 * write_bw)  (in single wb case)
1024          *     or equally: x_intercept = wb_setpoint + 8 * write_bw
1025          *
1026          * For single wb case, the dirty pages are observed to fluctuate
1027          * regularly within range
1028          *        [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
1029          * for various filesystems, where (2) can yield in a reasonable 12.5%
1030          * fluctuation range for pos_ratio.
1031          *
1032          * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
1033          * own size, so move the slope over accordingly and choose a slope that
1034          * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
1035          */
1036         if (unlikely(wb_thresh > dtc->thresh))
1037                 wb_thresh = dtc->thresh;
1038         /*
1039          * It's very possible that wb_thresh is close to 0 not because the
1040          * device is slow, but that it has remained inactive for long time.
1041          * Honour such devices a reasonable good (hopefully IO efficient)
1042          * threshold, so that the occasional writes won't be blocked and active
1043          * writes can rampup the threshold quickly.
1044          */
1045         wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
1046         /*
1047          * scale global setpoint to wb's:
1048          *      wb_setpoint = setpoint * wb_thresh / thresh
1049          */
1050         x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
1051         wb_setpoint = setpoint * (u64)x >> 16;
1052         /*
1053          * Use span=(8*write_bw) in single wb case as indicated by
1054          * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
1055          *
1056          *        wb_thresh                    thresh - wb_thresh
1057          * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
1058          *         thresh                           thresh
1059          */
1060         span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
1061         x_intercept = wb_setpoint + span;
1062
1063         if (dtc->wb_dirty < x_intercept - span / 4) {
1064                 pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
1065                                       (x_intercept - wb_setpoint) | 1);
1066         } else
1067                 pos_ratio /= 4;
1068
1069         /*
1070          * wb reserve area, safeguard against dirty pool underrun and disk idle
1071          * It may push the desired control point of global dirty pages higher
1072          * than setpoint.
1073          */
1074         x_intercept = wb_thresh / 2;
1075         if (dtc->wb_dirty < x_intercept) {
1076                 if (dtc->wb_dirty > x_intercept / 8)
1077                         pos_ratio = div_u64(pos_ratio * x_intercept,
1078                                             dtc->wb_dirty);
1079                 else
1080                         pos_ratio *= 8;
1081         }
1082
1083         dtc->pos_ratio = pos_ratio;
1084 }
1085
1086 static void wb_update_write_bandwidth(struct bdi_writeback *wb,
1087                                       unsigned long elapsed,
1088                                       unsigned long written)
1089 {
1090         const unsigned long period = roundup_pow_of_two(3 * HZ);
1091         unsigned long avg = wb->avg_write_bandwidth;
1092         unsigned long old = wb->write_bandwidth;
1093         u64 bw;
1094
1095         /*
1096          * bw = written * HZ / elapsed
1097          *
1098          *                   bw * elapsed + write_bandwidth * (period - elapsed)
1099          * write_bandwidth = ---------------------------------------------------
1100          *                                          period
1101          *
1102          * @written may have decreased due to account_page_redirty().
1103          * Avoid underflowing @bw calculation.
1104          */
1105         bw = written - min(written, wb->written_stamp);
1106         bw *= HZ;
1107         if (unlikely(elapsed > period)) {
1108                 do_div(bw, elapsed);
1109                 avg = bw;
1110                 goto out;
1111         }
1112         bw += (u64)wb->write_bandwidth * (period - elapsed);
1113         bw >>= ilog2(period);
1114
1115         /*
1116          * one more level of smoothing, for filtering out sudden spikes
1117          */
1118         if (avg > old && old >= (unsigned long)bw)
1119                 avg -= (avg - old) >> 3;
1120
1121         if (avg < old && old <= (unsigned long)bw)
1122                 avg += (old - avg) >> 3;
1123
1124 out:
1125         /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
1126         avg = max(avg, 1LU);
1127         if (wb_has_dirty_io(wb)) {
1128                 long delta = avg - wb->avg_write_bandwidth;
1129                 WARN_ON_ONCE(atomic_long_add_return(delta,
1130                                         &wb->bdi->tot_write_bandwidth) <= 0);
1131         }
1132         wb->write_bandwidth = bw;
1133         wb->avg_write_bandwidth = avg;
1134 }
1135
1136 static void update_dirty_limit(struct dirty_throttle_control *dtc)
1137 {
1138         struct wb_domain *dom = dtc_dom(dtc);
1139         unsigned long thresh = dtc->thresh;
1140         unsigned long limit = dom->dirty_limit;
1141
1142         /*
1143          * Follow up in one step.
1144          */
1145         if (limit < thresh) {
1146                 limit = thresh;
1147                 goto update;
1148         }
1149
1150         /*
1151          * Follow down slowly. Use the higher one as the target, because thresh
1152          * may drop below dirty. This is exactly the reason to introduce
1153          * dom->dirty_limit which is guaranteed to lie above the dirty pages.
1154          */
1155         thresh = max(thresh, dtc->dirty);
1156         if (limit > thresh) {
1157                 limit -= (limit - thresh) >> 5;
1158                 goto update;
1159         }
1160         return;
1161 update:
1162         dom->dirty_limit = limit;
1163 }
1164
1165 static void domain_update_bandwidth(struct dirty_throttle_control *dtc,
1166                                     unsigned long now)
1167 {
1168         struct wb_domain *dom = dtc_dom(dtc);
1169
1170         /*
1171          * check locklessly first to optimize away locking for the most time
1172          */
1173         if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
1174                 return;
1175
1176         spin_lock(&dom->lock);
1177         if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
1178                 update_dirty_limit(dtc);
1179                 dom->dirty_limit_tstamp = now;
1180         }
1181         spin_unlock(&dom->lock);
1182 }
1183
1184 /*
1185  * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
1186  *
1187  * Normal wb tasks will be curbed at or below it in long term.
1188  * Obviously it should be around (write_bw / N) when there are N dd tasks.
1189  */
1190 static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
1191                                       unsigned long dirtied,
1192                                       unsigned long elapsed)
1193 {
1194         struct bdi_writeback *wb = dtc->wb;
1195         unsigned long dirty = dtc->dirty;
1196         unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
1197         unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
1198         unsigned long setpoint = (freerun + limit) / 2;
1199         unsigned long write_bw = wb->avg_write_bandwidth;
1200         unsigned long dirty_ratelimit = wb->dirty_ratelimit;
1201         unsigned long dirty_rate;
1202         unsigned long task_ratelimit;
1203         unsigned long balanced_dirty_ratelimit;
1204         unsigned long step;
1205         unsigned long x;
1206         unsigned long shift;
1207
1208         /*
1209          * The dirty rate will match the writeout rate in long term, except
1210          * when dirty pages are truncated by userspace or re-dirtied by FS.
1211          */
1212         dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
1213
1214         /*
1215          * task_ratelimit reflects each dd's dirty rate for the past 200ms.
1216          */
1217         task_ratelimit = (u64)dirty_ratelimit *
1218                                         dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
1219         task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
1220
1221         /*
1222          * A linear estimation of the "balanced" throttle rate. The theory is,
1223          * if there are N dd tasks, each throttled at task_ratelimit, the wb's
1224          * dirty_rate will be measured to be (N * task_ratelimit). So the below
1225          * formula will yield the balanced rate limit (write_bw / N).
1226          *
1227          * Note that the expanded form is not a pure rate feedback:
1228          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate)              (1)
1229          * but also takes pos_ratio into account:
1230          *      rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
1231          *
1232          * (1) is not realistic because pos_ratio also takes part in balancing
1233          * the dirty rate.  Consider the state
1234          *      pos_ratio = 0.5                                              (3)
1235          *      rate = 2 * (write_bw / N)                                    (4)
1236          * If (1) is used, it will stuck in that state! Because each dd will
1237          * be throttled at
1238          *      task_ratelimit = pos_ratio * rate = (write_bw / N)           (5)
1239          * yielding
1240          *      dirty_rate = N * task_ratelimit = write_bw                   (6)
1241          * put (6) into (1) we get
1242          *      rate_(i+1) = rate_(i)                                        (7)
1243          *
1244          * So we end up using (2) to always keep
1245          *      rate_(i+1) ~= (write_bw / N)                                 (8)
1246          * regardless of the value of pos_ratio. As long as (8) is satisfied,
1247          * pos_ratio is able to drive itself to 1.0, which is not only where
1248          * the dirty count meet the setpoint, but also where the slope of
1249          * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
1250          */
1251         balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
1252                                            dirty_rate | 1);
1253         /*
1254          * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
1255          */
1256         if (unlikely(balanced_dirty_ratelimit > write_bw))
1257                 balanced_dirty_ratelimit = write_bw;
1258
1259         /*
1260          * We could safely do this and return immediately:
1261          *
1262          *      wb->dirty_ratelimit = balanced_dirty_ratelimit;
1263          *
1264          * However to get a more stable dirty_ratelimit, the below elaborated
1265          * code makes use of task_ratelimit to filter out singular points and
1266          * limit the step size.
1267          *
1268          * The below code essentially only uses the relative value of
1269          *
1270          *      task_ratelimit - dirty_ratelimit
1271          *      = (pos_ratio - 1) * dirty_ratelimit
1272          *
1273          * which reflects the direction and size of dirty position error.
1274          */
1275
1276         /*
1277          * dirty_ratelimit will follow balanced_dirty_ratelimit iff
1278          * task_ratelimit is on the same side of dirty_ratelimit, too.
1279          * For example, when
1280          * - dirty_ratelimit > balanced_dirty_ratelimit
1281          * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
1282          * lowering dirty_ratelimit will help meet both the position and rate
1283          * control targets. Otherwise, don't update dirty_ratelimit if it will
1284          * only help meet the rate target. After all, what the users ultimately
1285          * feel and care are stable dirty rate and small position error.
1286          *
1287          * |task_ratelimit - dirty_ratelimit| is used to limit the step size
1288          * and filter out the singular points of balanced_dirty_ratelimit. Which
1289          * keeps jumping around randomly and can even leap far away at times
1290          * due to the small 200ms estimation period of dirty_rate (we want to
1291          * keep that period small to reduce time lags).
1292          */
1293         step = 0;
1294
1295         /*
1296          * For strictlimit case, calculations above were based on wb counters
1297          * and limits (starting from pos_ratio = wb_position_ratio() and up to
1298          * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
1299          * Hence, to calculate "step" properly, we have to use wb_dirty as
1300          * "dirty" and wb_setpoint as "setpoint".
1301          *
1302          * We rampup dirty_ratelimit forcibly if wb_dirty is low because
1303          * it's possible that wb_thresh is close to zero due to inactivity
1304          * of backing device.
1305          */
1306         if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
1307                 dirty = dtc->wb_dirty;
1308                 if (dtc->wb_dirty < 8)
1309                         setpoint = dtc->wb_dirty + 1;
1310                 else
1311                         setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
1312         }
1313
1314         if (dirty < setpoint) {
1315                 x = min3(wb->balanced_dirty_ratelimit,
1316                          balanced_dirty_ratelimit, task_ratelimit);
1317                 if (dirty_ratelimit < x)
1318                         step = x - dirty_ratelimit;
1319         } else {
1320                 x = max3(wb->balanced_dirty_ratelimit,
1321                          balanced_dirty_ratelimit, task_ratelimit);
1322                 if (dirty_ratelimit > x)
1323                         step = dirty_ratelimit - x;
1324         }
1325
1326         /*
1327          * Don't pursue 100% rate matching. It's impossible since the balanced
1328          * rate itself is constantly fluctuating. So decrease the track speed
1329          * when it gets close to the target. Helps eliminate pointless tremors.
1330          */
1331         shift = dirty_ratelimit / (2 * step + 1);
1332         if (shift < BITS_PER_LONG)
1333                 step = DIV_ROUND_UP(step >> shift, 8);
1334         else
1335                 step = 0;
1336
1337         if (dirty_ratelimit < balanced_dirty_ratelimit)
1338                 dirty_ratelimit += step;
1339         else
1340                 dirty_ratelimit -= step;
1341
1342         wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
1343         wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
1344
1345         trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
1346 }
1347
1348 static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
1349                                   struct dirty_throttle_control *mdtc,
1350                                   unsigned long start_time,
1351                                   bool update_ratelimit)
1352 {
1353         struct bdi_writeback *wb = gdtc->wb;
1354         unsigned long now = jiffies;
1355         unsigned long elapsed = now - wb->bw_time_stamp;
1356         unsigned long dirtied;
1357         unsigned long written;
1358
1359         lockdep_assert_held(&wb->list_lock);
1360
1361         /*
1362          * rate-limit, only update once every 200ms.
1363          */
1364         if (elapsed < BANDWIDTH_INTERVAL)
1365                 return;
1366
1367         dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
1368         written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
1369
1370         /*
1371          * Skip quiet periods when disk bandwidth is under-utilized.
1372          * (at least 1s idle time between two flusher runs)
1373          */
1374         if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
1375                 goto snapshot;
1376
1377         if (update_ratelimit) {
1378                 domain_update_bandwidth(gdtc, now);
1379                 wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);
1380
1381                 /*
1382                  * @mdtc is always NULL if !CGROUP_WRITEBACK but the
1383                  * compiler has no way to figure that out.  Help it.
1384                  */
1385                 if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
1386                         domain_update_bandwidth(mdtc, now);
1387                         wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
1388                 }
1389         }
1390         wb_update_write_bandwidth(wb, elapsed, written);
1391
1392 snapshot:
1393         wb->dirtied_stamp = dirtied;
1394         wb->written_stamp = written;
1395         wb->bw_time_stamp = now;
1396 }
1397
1398 void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
1399 {
1400         struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };
1401
1402         __wb_update_bandwidth(&gdtc, NULL, start_time, false);
1403 }
1404
1405 /*
1406  * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
1407  * will look to see if it needs to start dirty throttling.
1408  *
1409  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
1410  * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
1411  * (the number of pages we may dirty without exceeding the dirty limits).
1412  */
1413 static unsigned long dirty_poll_interval(unsigned long dirty,
1414                                          unsigned long thresh)
1415 {
1416         if (thresh > dirty)
1417                 return 1UL << (ilog2(thresh - dirty) >> 1);
1418
1419         return 1;
1420 }
1421
1422 static unsigned long wb_max_pause(struct bdi_writeback *wb,
1423                                   unsigned long wb_dirty)
1424 {
1425         unsigned long bw = wb->avg_write_bandwidth;
1426         unsigned long t;
1427
1428         /*
1429          * Limit pause time for small memory systems. If sleeping for too long
1430          * time, a small pool of dirty/writeback pages may go empty and disk go
1431          * idle.
1432          *
1433          * 8 serves as the safety ratio.
1434          */
1435         t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
1436         t++;
1437
1438         return min_t(unsigned long, t, MAX_PAUSE);
1439 }
1440
1441 static long wb_min_pause(struct bdi_writeback *wb,
1442                          long max_pause,
1443                          unsigned long task_ratelimit,
1444                          unsigned long dirty_ratelimit,
1445                          int *nr_dirtied_pause)
1446 {
1447         long hi = ilog2(wb->avg_write_bandwidth);
1448         long lo = ilog2(wb->dirty_ratelimit);
1449         long t;         /* target pause */
1450         long pause;     /* estimated next pause */
1451         int pages;      /* target nr_dirtied_pause */
1452
1453         /* target for 10ms pause on 1-dd case */
1454         t = max(1, HZ / 100);
1455
1456         /*
1457          * Scale up pause time for concurrent dirtiers in order to reduce CPU
1458          * overheads.
1459          *
1460          * (N * 10ms) on 2^N concurrent tasks.
1461          */
1462         if (hi > lo)
1463                 t += (hi - lo) * (10 * HZ) / 1024;
1464
1465         /*
1466          * This is a bit convoluted. We try to base the next nr_dirtied_pause
1467          * on the much more stable dirty_ratelimit. However the next pause time
1468          * will be computed based on task_ratelimit and the two rate limits may
1469          * depart considerably at some time. Especially if task_ratelimit goes
1470          * below dirty_ratelimit/2 and the target pause is max_pause, the next
1471          * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
1472          * result task_ratelimit won't be executed faithfully, which could
1473          * eventually bring down dirty_ratelimit.
1474          *
1475          * We apply two rules to fix it up:
1476          * 1) try to estimate the next pause time and if necessary, use a lower
1477          *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
1478          *    nr_dirtied_pause will be "dancing" with task_ratelimit.
1479          * 2) limit the target pause time to max_pause/2, so that the normal
1480          *    small fluctuations of task_ratelimit won't trigger rule (1) and
1481          *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
1482          */
1483         t = min(t, 1 + max_pause / 2);
1484         pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1485
1486         /*
1487          * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
1488          * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
1489          * When the 16 consecutive reads are often interrupted by some dirty
1490          * throttling pause during the async writes, cfq will go into idles
1491          * (deadline is fine). So push nr_dirtied_pause as high as possible
1492          * until reaches DIRTY_POLL_THRESH=32 pages.
1493          */
1494         if (pages < DIRTY_POLL_THRESH) {
1495                 t = max_pause;
1496                 pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
1497                 if (pages > DIRTY_POLL_THRESH) {
1498                         pages = DIRTY_POLL_THRESH;
1499                         t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
1500                 }
1501         }
1502
1503         pause = HZ * pages / (task_ratelimit + 1);
1504         if (pause > max_pause) {
1505                 t = max_pause;
1506                 pages = task_ratelimit * t / roundup_pow_of_two(HZ);
1507         }
1508
1509         *nr_dirtied_pause = pages;
1510         /*
1511          * The minimal pause time will normally be half the target pause time.
1512          */
1513         return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
1514 }
1515
1516 static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
1517 {
1518         struct bdi_writeback *wb = dtc->wb;
1519         unsigned long wb_reclaimable;
1520
1521         /*
1522          * wb_thresh is not treated as some limiting factor as
1523          * dirty_thresh, due to reasons
1524          * - in JBOD setup, wb_thresh can fluctuate a lot
1525          * - in a system with HDD and USB key, the USB key may somehow
1526          *   go into state (wb_dirty >> wb_thresh) either because
1527          *   wb_dirty starts high, or because wb_thresh drops low.
1528          *   In this case we don't want to hard throttle the USB key
1529          *   dirtiers for 100 seconds until wb_dirty drops under
1530          *   wb_thresh. Instead the auxiliary wb control line in
1531          *   wb_position_ratio() will let the dirtier task progress
1532          *   at some rate <= (write_bw / 2) for bringing down wb_dirty.
1533          */
1534         dtc->wb_thresh = __wb_calc_thresh(dtc);
1535         dtc->wb_bg_thresh = dtc->thresh ?
1536                 div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;
1537
1538         /*
1539          * In order to avoid the stacked BDI deadlock we need
1540          * to ensure we accurately count the 'dirty' pages when
1541          * the threshold is low.
1542          *
1543          * Otherwise it would be possible to get thresh+n pages
1544          * reported dirty, even though there are thresh-m pages
1545          * actually dirty; with m+n sitting in the percpu
1546          * deltas.
1547          */
1548         if (dtc->wb_thresh < 2 * wb_stat_error(wb)) {
1549                 wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
1550                 dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
1551         } else {
1552                 wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
1553                 dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
1554         }
1555 }
1556
1557 /*
1558  * balance_dirty_pages() must be called by processes which are generating dirty
1559  * data.  It looks at the number of dirty pages in the machine and will force
1560  * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
1561  * If we're over `background_thresh' then the writeback threads are woken to
1562  * perform some writeout.
1563  */
1564 static void balance_dirty_pages(struct bdi_writeback *wb,
1565                                 unsigned long pages_dirtied)
1566 {
1567         struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1568         struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1569         struct dirty_throttle_control * const gdtc = &gdtc_stor;
1570         struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1571                                                      &mdtc_stor : NULL;
1572         struct dirty_throttle_control *sdtc;
1573         unsigned long nr_reclaimable;   /* = file_dirty + unstable_nfs */
1574         long period;
1575         long pause;
1576         long max_pause;
1577         long min_pause;
1578         int nr_dirtied_pause;
1579         bool dirty_exceeded = false;
1580         unsigned long task_ratelimit;
1581         unsigned long dirty_ratelimit;
1582         struct backing_dev_info *bdi = wb->bdi;
1583         bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
1584         unsigned long start_time = jiffies;
1585
1586         for (;;) {
1587                 unsigned long now = jiffies;
1588                 unsigned long dirty, thresh, bg_thresh;
1589                 unsigned long m_dirty = 0;      /* stop bogus uninit warnings */
1590                 unsigned long m_thresh = 0;
1591                 unsigned long m_bg_thresh = 0;
1592
1593                 /*
1594                  * Unstable writes are a feature of certain networked
1595                  * filesystems (i.e. NFS) in which data may have been
1596                  * written to the server's write cache, but has not yet
1597                  * been flushed to permanent storage.
1598                  */
1599                 nr_reclaimable = global_node_page_state(NR_FILE_DIRTY) +
1600                                         global_node_page_state(NR_UNSTABLE_NFS);
1601                 gdtc->avail = global_dirtyable_memory();
1602                 gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);
1603
1604                 domain_dirty_limits(gdtc);
1605
1606                 if (unlikely(strictlimit)) {
1607                         wb_dirty_limits(gdtc);
1608
1609                         dirty = gdtc->wb_dirty;
1610                         thresh = gdtc->wb_thresh;
1611                         bg_thresh = gdtc->wb_bg_thresh;
1612                 } else {
1613                         dirty = gdtc->dirty;
1614                         thresh = gdtc->thresh;
1615                         bg_thresh = gdtc->bg_thresh;
1616                 }
1617
1618                 if (mdtc) {
1619                         unsigned long filepages, headroom, writeback;
1620
1621                         /*
1622                          * If @wb belongs to !root memcg, repeat the same
1623                          * basic calculations for the memcg domain.
1624                          */
1625                         mem_cgroup_wb_stats(wb, &filepages, &headroom,
1626                                             &mdtc->dirty, &writeback);
1627                         mdtc->dirty += writeback;
1628                         mdtc_calc_avail(mdtc, filepages, headroom);
1629
1630                         domain_dirty_limits(mdtc);
1631
1632                         if (unlikely(strictlimit)) {
1633                                 wb_dirty_limits(mdtc);
1634                                 m_dirty = mdtc->wb_dirty;
1635                                 m_thresh = mdtc->wb_thresh;
1636                                 m_bg_thresh = mdtc->wb_bg_thresh;
1637                         } else {
1638                                 m_dirty = mdtc->dirty;
1639                                 m_thresh = mdtc->thresh;
1640                                 m_bg_thresh = mdtc->bg_thresh;
1641                         }
1642                 }
1643
1644                 /*
1645                  * Throttle it only when the background writeback cannot
1646                  * catch-up. This avoids (excessively) small writeouts
1647                  * when the wb limits are ramping up in case of !strictlimit.
1648                  *
1649                  * In strictlimit case make decision based on the wb counters
1650                  * and limits. Small writeouts when the wb limits are ramping
1651                  * up are the price we consciously pay for strictlimit-ing.
1652                  *
1653                  * If memcg domain is in effect, @dirty should be under
1654                  * both global and memcg freerun ceilings.
1655                  */
1656                 if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
1657                     (!mdtc ||
1658                      m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
1659                         unsigned long intv = dirty_poll_interval(dirty, thresh);
1660                         unsigned long m_intv = ULONG_MAX;
1661
1662                         current->dirty_paused_when = now;
1663                         current->nr_dirtied = 0;
1664                         if (mdtc)
1665                                 m_intv = dirty_poll_interval(m_dirty, m_thresh);
1666                         current->nr_dirtied_pause = min(intv, m_intv);
1667                         break;
1668                 }
1669
1670                 if (unlikely(!writeback_in_progress(wb)))
1671                         wb_start_background_writeback(wb);
1672
1673                 /*
1674                  * Calculate global domain's pos_ratio and select the
1675                  * global dtc by default.
1676                  */
1677                 if (!strictlimit)
1678                         wb_dirty_limits(gdtc);
1679
1680                 dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
1681                         ((gdtc->dirty > gdtc->thresh) || strictlimit);
1682
1683                 wb_position_ratio(gdtc);
1684                 sdtc = gdtc;
1685
1686                 if (mdtc) {
1687                         /*
1688                          * If memcg domain is in effect, calculate its
1689                          * pos_ratio.  @wb should satisfy constraints from
1690                          * both global and memcg domains.  Choose the one
1691                          * w/ lower pos_ratio.
1692                          */
1693                         if (!strictlimit)
1694                                 wb_dirty_limits(mdtc);
1695
1696                         dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
1697                                 ((mdtc->dirty > mdtc->thresh) || strictlimit);
1698
1699                         wb_position_ratio(mdtc);
1700                         if (mdtc->pos_ratio < gdtc->pos_ratio)
1701                                 sdtc = mdtc;
1702                 }
1703
1704                 if (dirty_exceeded && !wb->dirty_exceeded)
1705                         wb->dirty_exceeded = 1;
1706
1707                 if (time_is_before_jiffies(wb->bw_time_stamp +
1708                                            BANDWIDTH_INTERVAL)) {
1709                         spin_lock(&wb->list_lock);
1710                         __wb_update_bandwidth(gdtc, mdtc, start_time, true);
1711                         spin_unlock(&wb->list_lock);
1712                 }
1713
1714                 /* throttle according to the chosen dtc */
1715                 dirty_ratelimit = wb->dirty_ratelimit;
1716                 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
1717                                                         RATELIMIT_CALC_SHIFT;
1718                 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
1719                 min_pause = wb_min_pause(wb, max_pause,
1720                                          task_ratelimit, dirty_ratelimit,
1721                                          &nr_dirtied_pause);
1722
1723                 if (unlikely(task_ratelimit == 0)) {
1724                         period = max_pause;
1725                         pause = max_pause;
1726                         goto pause;
1727                 }
1728                 period = HZ * pages_dirtied / task_ratelimit;
1729                 pause = period;
1730                 if (current->dirty_paused_when)
1731                         pause -= now - current->dirty_paused_when;
1732                 /*
1733                  * For less than 1s think time (ext3/4 may block the dirtier
1734                  * for up to 800ms from time to time on 1-HDD; so does xfs,
1735                  * however at much less frequency), try to compensate it in
1736                  * future periods by updating the virtual time; otherwise just
1737                  * do a reset, as it may be a light dirtier.
1738                  */
1739                 if (pause < min_pause) {
1740                         trace_balance_dirty_pages(wb,
1741                                                   sdtc->thresh,
1742                                                   sdtc->bg_thresh,
1743                                                   sdtc->dirty,
1744                                                   sdtc->wb_thresh,
1745                                                   sdtc->wb_dirty,
1746                                                   dirty_ratelimit,
1747                                                   task_ratelimit,
1748                                                   pages_dirtied,
1749                                                   period,
1750                                                   min(pause, 0L),
1751                                                   start_time);
1752                         if (pause < -HZ) {
1753                                 current->dirty_paused_when = now;
1754                                 current->nr_dirtied = 0;
1755                         } else if (period) {
1756                                 current->dirty_paused_when += period;
1757                                 current->nr_dirtied = 0;
1758                         } else if (current->nr_dirtied_pause <= pages_dirtied)
1759                                 current->nr_dirtied_pause += pages_dirtied;
1760                         break;
1761                 }
1762                 if (unlikely(pause > max_pause)) {
1763                         /* for occasional dropped task_ratelimit */
1764                         now += min(pause - max_pause, max_pause);
1765                         pause = max_pause;
1766                 }
1767
1768 pause:
1769                 trace_balance_dirty_pages(wb,
1770                                           sdtc->thresh,
1771                                           sdtc->bg_thresh,
1772                                           sdtc->dirty,
1773                                           sdtc->wb_thresh,
1774                                           sdtc->wb_dirty,
1775                                           dirty_ratelimit,
1776                                           task_ratelimit,
1777                                           pages_dirtied,
1778                                           period,
1779                                           pause,
1780                                           start_time);
1781                 __set_current_state(TASK_KILLABLE);
1782                 wb->dirty_sleep = now;
1783                 io_schedule_timeout(pause);
1784
1785                 current->dirty_paused_when = now + pause;
1786                 current->nr_dirtied = 0;
1787                 current->nr_dirtied_pause = nr_dirtied_pause;
1788
1789                 /*
1790                  * This is typically equal to (dirty < thresh) and can also
1791                  * keep "1000+ dd on a slow USB stick" under control.
1792                  */
1793                 if (task_ratelimit)
1794                         break;
1795
1796                 /*
1797                  * In the case of an unresponding NFS server and the NFS dirty
1798                  * pages exceeds dirty_thresh, give the other good wb's a pipe
1799                  * to go through, so that tasks on them still remain responsive.
1800                  *
1801                  * In theory 1 page is enough to keep the consumer-producer
1802                  * pipe going: the flusher cleans 1 page => the task dirties 1
1803                  * more page. However wb_dirty has accounting errors.  So use
1804                  * the larger and more IO friendly wb_stat_error.
1805                  */
1806                 if (sdtc->wb_dirty <= wb_stat_error(wb))
1807                         break;
1808
1809                 if (fatal_signal_pending(current))
1810                         break;
1811         }
1812
1813         if (!dirty_exceeded && wb->dirty_exceeded)
1814                 wb->dirty_exceeded = 0;
1815
1816         if (writeback_in_progress(wb))
1817                 return;
1818
1819         /*
1820          * In laptop mode, we wait until hitting the higher threshold before
1821          * starting background writeout, and then write out all the way down
1822          * to the lower threshold.  So slow writers cause minimal disk activity.
1823          *
1824          * In normal mode, we start background writeout at the lower
1825          * background_thresh, to keep the amount of dirty memory low.
1826          */
1827         if (laptop_mode)
1828                 return;
1829
1830         if (nr_reclaimable > gdtc->bg_thresh)
1831                 wb_start_background_writeback(wb);
1832 }
1833
1834 static DEFINE_PER_CPU(int, bdp_ratelimits);
1835
1836 /*
1837  * Normal tasks are throttled by
1838  *      loop {
1839  *              dirty tsk->nr_dirtied_pause pages;
1840  *              take a snap in balance_dirty_pages();
1841  *      }
1842  * However there is a worst case. If every task exit immediately when dirtied
1843  * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
1844  * called to throttle the page dirties. The solution is to save the not yet
1845  * throttled page dirties in dirty_throttle_leaks on task exit and charge them
1846  * randomly into the running tasks. This works well for the above worst case,
1847  * as the new task will pick up and accumulate the old task's leaked dirty
1848  * count and eventually get throttled.
1849  */
1850 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
1851
1852 /**
1853  * balance_dirty_pages_ratelimited - balance dirty memory state
1854  * @mapping: address_space which was dirtied
1855  *
1856  * Processes which are dirtying memory should call in here once for each page
1857  * which was newly dirtied.  The function will periodically check the system's
1858  * dirty state and will initiate writeback if needed.
1859  *
1860  * On really big machines, get_writeback_state is expensive, so try to avoid
1861  * calling it too often (ratelimiting).  But once we're over the dirty memory
1862  * limit we decrease the ratelimiting by a lot, to prevent individual processes
1863  * from overshooting the limit by (ratelimit_pages) each.
1864  */
1865 void balance_dirty_pages_ratelimited(struct address_space *mapping)
1866 {
1867         struct inode *inode = mapping->host;
1868         struct backing_dev_info *bdi = inode_to_bdi(inode);
1869         struct bdi_writeback *wb = NULL;
1870         int ratelimit;
1871         int *p;
1872
1873         if (!bdi_cap_account_dirty(bdi))
1874                 return;
1875
1876         if (inode_cgwb_enabled(inode))
1877                 wb = wb_get_create_current(bdi, GFP_KERNEL);
1878         if (!wb)
1879                 wb = &bdi->wb;
1880
1881         ratelimit = current->nr_dirtied_pause;
1882         if (wb->dirty_exceeded)
1883                 ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
1884
1885         preempt_disable();
1886         /*
1887          * This prevents one CPU to accumulate too many dirtied pages without
1888          * calling into balance_dirty_pages(), which can happen when there are
1889          * 1000+ tasks, all of them start dirtying pages at exactly the same
1890          * time, hence all honoured too large initial task->nr_dirtied_pause.
1891          */
1892         p =  this_cpu_ptr(&bdp_ratelimits);
1893         if (unlikely(current->nr_dirtied >= ratelimit))
1894                 *p = 0;
1895         else if (unlikely(*p >= ratelimit_pages)) {
1896                 *p = 0;
1897                 ratelimit = 0;
1898         }
1899         /*
1900          * Pick up the dirtied pages by the exited tasks. This avoids lots of
1901          * short-lived tasks (eg. gcc invocations in a kernel build) escaping
1902          * the dirty throttling and livelock other long-run dirtiers.
1903          */
1904         p = this_cpu_ptr(&dirty_throttle_leaks);
1905         if (*p > 0 && current->nr_dirtied < ratelimit) {
1906                 unsigned long nr_pages_dirtied;
1907                 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
1908                 *p -= nr_pages_dirtied;
1909                 current->nr_dirtied += nr_pages_dirtied;
1910         }
1911         preempt_enable();
1912
1913         if (unlikely(current->nr_dirtied >= ratelimit))
1914                 balance_dirty_pages(wb, current->nr_dirtied);
1915
1916         wb_put(wb);
1917 }
1918 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
1919
1920 /**
1921  * wb_over_bg_thresh - does @wb need to be written back?
1922  * @wb: bdi_writeback of interest
1923  *
1924  * Determines whether background writeback should keep writing @wb or it's
1925  * clean enough.  Returns %true if writeback should continue.
1926  */
1927 bool wb_over_bg_thresh(struct bdi_writeback *wb)
1928 {
1929         struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
1930         struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
1931         struct dirty_throttle_control * const gdtc = &gdtc_stor;
1932         struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
1933                                                      &mdtc_stor : NULL;
1934
1935         /*
1936          * Similar to balance_dirty_pages() but ignores pages being written
1937          * as we're trying to decide whether to put more under writeback.
1938          */
1939         gdtc->avail = global_dirtyable_memory();
1940         gdtc->dirty = global_node_page_state(NR_FILE_DIRTY) +
1941                       global_node_page_state(NR_UNSTABLE_NFS);
1942         domain_dirty_limits(gdtc);
1943
1944         if (gdtc->dirty > gdtc->bg_thresh)
1945                 return true;
1946
1947         if (wb_stat(wb, WB_RECLAIMABLE) >
1948             wb_calc_thresh(gdtc->wb, gdtc->bg_thresh))
1949                 return true;
1950
1951         if (mdtc) {
1952                 unsigned long filepages, headroom, writeback;
1953
1954                 mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
1955                                     &writeback);
1956                 mdtc_calc_avail(mdtc, filepages, headroom);
1957                 domain_dirty_limits(mdtc);      /* ditto, ignore writeback */
1958
1959                 if (mdtc->dirty > mdtc->bg_thresh)
1960                         return true;
1961
1962                 if (wb_stat(wb, WB_RECLAIMABLE) >
1963                     wb_calc_thresh(mdtc->wb, mdtc->bg_thresh))
1964                         return true;
1965         }
1966
1967         return false;
1968 }
1969
1970 /*
1971  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
1972  */
1973 int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
1974         void __user *buffer, size_t *length, loff_t *ppos)
1975 {
1976         unsigned int old_interval = dirty_writeback_interval;
1977         int ret;
1978
1979         ret = proc_dointvec(table, write, buffer, length, ppos);
1980
1981         /*
1982          * Writing 0 to dirty_writeback_interval will disable periodic writeback
1983          * and a different non-zero value will wakeup the writeback threads.
1984          * wb_wakeup_delayed() would be more appropriate, but it's a pain to
1985          * iterate over all bdis and wbs.
1986          * The reason we do this is to make the change take effect immediately.
1987          */
1988         if (!ret && write && dirty_writeback_interval &&
1989                 dirty_writeback_interval != old_interval)
1990                 wakeup_flusher_threads(WB_REASON_PERIODIC);
1991
1992         return ret;
1993 }
1994
1995 #ifdef CONFIG_BLOCK
1996 void laptop_mode_timer_fn(unsigned long data)
1997 {
1998         struct request_queue *q = (struct request_queue *)data;
1999
2000         wakeup_flusher_threads_bdi(q->backing_dev_info, WB_REASON_LAPTOP_TIMER);
2001 }
2002
2003 /*
2004  * We've spun up the disk and we're in laptop mode: schedule writeback
2005  * of all dirty data a few seconds from now.  If the flush is already scheduled
2006  * then push it back - the user is still using the disk.
2007  */
2008 void laptop_io_completion(struct backing_dev_info *info)
2009 {
2010         mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
2011 }
2012
2013 /*
2014  * We're in laptop mode and we've just synced. The sync's writes will have
2015  * caused another writeback to be scheduled by laptop_io_completion.
2016  * Nothing needs to be written back anymore, so we unschedule the writeback.
2017  */
2018 void laptop_sync_completion(void)
2019 {
2020         struct backing_dev_info *bdi;
2021
2022         rcu_read_lock();
2023
2024         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2025                 del_timer(&bdi->laptop_mode_wb_timer);
2026
2027         rcu_read_unlock();
2028 }
2029 #endif
2030
2031 /*
2032  * If ratelimit_pages is too high then we can get into dirty-data overload
2033  * if a large number of processes all perform writes at the same time.
2034  * If it is too low then SMP machines will call the (expensive)
2035  * get_writeback_state too often.
2036  *
2037  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
2038  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
2039  * thresholds.
2040  */
2041
2042 void writeback_set_ratelimit(void)
2043 {
2044         struct wb_domain *dom = &global_wb_domain;
2045         unsigned long background_thresh;
2046         unsigned long dirty_thresh;
2047
2048         global_dirty_limits(&background_thresh, &dirty_thresh);
2049         dom->dirty_limit = dirty_thresh;
2050         ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
2051         if (ratelimit_pages < 16)
2052                 ratelimit_pages = 16;
2053 }
2054
2055 static int page_writeback_cpu_online(unsigned int cpu)
2056 {
2057         writeback_set_ratelimit();
2058         return 0;
2059 }
2060
2061 /*
2062  * Called early on to tune the page writeback dirty limits.
2063  *
2064  * We used to scale dirty pages according to how total memory
2065  * related to pages that could be allocated for buffers (by
2066  * comparing nr_free_buffer_pages() to vm_total_pages.
2067  *
2068  * However, that was when we used "dirty_ratio" to scale with
2069  * all memory, and we don't do that any more. "dirty_ratio"
2070  * is now applied to total non-HIGHPAGE memory (by subtracting
2071  * totalhigh_pages from vm_total_pages), and as such we can't
2072  * get into the old insane situation any more where we had
2073  * large amounts of dirty pages compared to a small amount of
2074  * non-HIGHMEM memory.
2075  *
2076  * But we might still want to scale the dirty_ratio by how
2077  * much memory the box has..
2078  */
2079 void __init page_writeback_init(void)
2080 {
2081         BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
2082
2083         cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
2084                           page_writeback_cpu_online, NULL);
2085         cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
2086                           page_writeback_cpu_online);
2087 }
2088
2089 /**
2090  * tag_pages_for_writeback - tag pages to be written by write_cache_pages
2091  * @mapping: address space structure to write
2092  * @start: starting page index
2093  * @end: ending page index (inclusive)
2094  *
2095  * This function scans the page range from @start to @end (inclusive) and tags
2096  * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
2097  * that write_cache_pages (or whoever calls this function) will then use
2098  * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
2099  * used to avoid livelocking of writeback by a process steadily creating new
2100  * dirty pages in the file (thus it is important for this function to be quick
2101  * so that it can tag pages faster than a dirtying process can create them).
2102  */
2103 /*
2104  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
2105  */
2106 void tag_pages_for_writeback(struct address_space *mapping,
2107                              pgoff_t start, pgoff_t end)
2108 {
2109 #define WRITEBACK_TAG_BATCH 4096
2110         unsigned long tagged = 0;
2111         struct radix_tree_iter iter;
2112         void **slot;
2113
2114         spin_lock_irq(&mapping->tree_lock);
2115         radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, start,
2116                                                         PAGECACHE_TAG_DIRTY) {
2117                 if (iter.index > end)
2118                         break;
2119                 radix_tree_iter_tag_set(&mapping->page_tree, &iter,
2120                                                         PAGECACHE_TAG_TOWRITE);
2121                 tagged++;
2122                 if ((tagged % WRITEBACK_TAG_BATCH) != 0)
2123                         continue;
2124                 slot = radix_tree_iter_resume(slot, &iter);
2125                 spin_unlock_irq(&mapping->tree_lock);
2126                 cond_resched();
2127                 spin_lock_irq(&mapping->tree_lock);
2128         }
2129         spin_unlock_irq(&mapping->tree_lock);
2130 }
2131 EXPORT_SYMBOL(tag_pages_for_writeback);
2132
2133 /**
2134  * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
2135  * @mapping: address space structure to write
2136  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2137  * @writepage: function called for each page
2138  * @data: data passed to writepage function
2139  *
2140  * If a page is already under I/O, write_cache_pages() skips it, even
2141  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
2142  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
2143  * and msync() need to guarantee that all the data which was dirty at the time
2144  * the call was made get new I/O started against them.  If wbc->sync_mode is
2145  * WB_SYNC_ALL then we were called for data integrity and we must wait for
2146  * existing IO to complete.
2147  *
2148  * To avoid livelocks (when other process dirties new pages), we first tag
2149  * pages which should be written back with TOWRITE tag and only then start
2150  * writing them. For data-integrity sync we have to be careful so that we do
2151  * not miss some pages (e.g., because some other process has cleared TOWRITE
2152  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
2153  * by the process clearing the DIRTY tag (and submitting the page for IO).
2154  */
2155 int write_cache_pages(struct address_space *mapping,
2156                       struct writeback_control *wbc, writepage_t writepage,
2157                       void *data)
2158 {
2159         int ret = 0;
2160         int done = 0;
2161         struct pagevec pvec;
2162         int nr_pages;
2163         pgoff_t uninitialized_var(writeback_index);
2164         pgoff_t index;
2165         pgoff_t end;            /* Inclusive */
2166         pgoff_t done_index;
2167         int cycled;
2168         int range_whole = 0;
2169         int tag;
2170
2171         pagevec_init(&pvec, 0);
2172         if (wbc->range_cyclic) {
2173                 writeback_index = mapping->writeback_index; /* prev offset */
2174                 index = writeback_index;
2175                 if (index == 0)
2176                         cycled = 1;
2177                 else
2178                         cycled = 0;
2179                 end = -1;
2180         } else {
2181                 index = wbc->range_start >> PAGE_SHIFT;
2182                 end = wbc->range_end >> PAGE_SHIFT;
2183                 if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
2184                         range_whole = 1;
2185                 cycled = 1; /* ignore range_cyclic tests */
2186         }
2187         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2188                 tag = PAGECACHE_TAG_TOWRITE;
2189         else
2190                 tag = PAGECACHE_TAG_DIRTY;
2191 retry:
2192         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
2193                 tag_pages_for_writeback(mapping, index, end);
2194         done_index = index;
2195         while (!done && (index <= end)) {
2196                 int i;
2197
2198                 nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
2199                                 tag);
2200                 if (nr_pages == 0)
2201                         break;
2202
2203                 for (i = 0; i < nr_pages; i++) {
2204                         struct page *page = pvec.pages[i];
2205
2206                         done_index = page->index;
2207
2208                         lock_page(page);
2209
2210                         /*
2211                          * Page truncated or invalidated. We can freely skip it
2212                          * then, even for data integrity operations: the page
2213                          * has disappeared concurrently, so there could be no
2214                          * real expectation of this data interity operation
2215                          * even if there is now a new, dirty page at the same
2216                          * pagecache address.
2217                          */
2218                         if (unlikely(page->mapping != mapping)) {
2219 continue_unlock:
2220                                 unlock_page(page);
2221                                 continue;
2222                         }
2223
2224                         if (!PageDirty(page)) {
2225                                 /* someone wrote it for us */
2226                                 goto continue_unlock;
2227                         }
2228
2229                         if (PageWriteback(page)) {
2230                                 if (wbc->sync_mode != WB_SYNC_NONE)
2231                                         wait_on_page_writeback(page);
2232                                 else
2233                                         goto continue_unlock;
2234                         }
2235
2236                         BUG_ON(PageWriteback(page));
2237                         if (!clear_page_dirty_for_io(page))
2238                                 goto continue_unlock;
2239
2240                         trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
2241                         ret = (*writepage)(page, wbc, data);
2242                         if (unlikely(ret)) {
2243                                 if (ret == AOP_WRITEPAGE_ACTIVATE) {
2244                                         unlock_page(page);
2245                                         ret = 0;
2246                                 } else {
2247                                         /*
2248                                          * done_index is set past this page,
2249                                          * so media errors will not choke
2250                                          * background writeout for the entire
2251                                          * file. This has consequences for
2252                                          * range_cyclic semantics (ie. it may
2253                                          * not be suitable for data integrity
2254                                          * writeout).
2255                                          */
2256                                         done_index = page->index + 1;
2257                                         done = 1;
2258                                         break;
2259                                 }
2260                         }
2261
2262                         /*
2263                          * We stop writing back only if we are not doing
2264                          * integrity sync. In case of integrity sync we have to
2265                          * keep going until we have written all the pages
2266                          * we tagged for writeback prior to entering this loop.
2267                          */
2268                         if (--wbc->nr_to_write <= 0 &&
2269                             wbc->sync_mode == WB_SYNC_NONE) {
2270                                 done = 1;
2271                                 break;
2272                         }
2273                 }
2274                 pagevec_release(&pvec);
2275                 cond_resched();
2276         }
2277         if (!cycled && !done) {
2278                 /*
2279                  * range_cyclic:
2280                  * We hit the last page and there is more work to be done: wrap
2281                  * back to the start of the file
2282                  */
2283                 cycled = 1;
2284                 index = 0;
2285                 end = writeback_index - 1;
2286                 goto retry;
2287         }
2288         if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
2289                 mapping->writeback_index = done_index;
2290
2291         return ret;
2292 }
2293 EXPORT_SYMBOL(write_cache_pages);
2294
2295 /*
2296  * Function used by generic_writepages to call the real writepage
2297  * function and set the mapping flags on error
2298  */
2299 static int __writepage(struct page *page, struct writeback_control *wbc,
2300                        void *data)
2301 {
2302         struct address_space *mapping = data;
2303         int ret = mapping->a_ops->writepage(page, wbc);
2304         mapping_set_error(mapping, ret);
2305         return ret;
2306 }
2307
2308 /**
2309  * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
2310  * @mapping: address space structure to write
2311  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
2312  *
2313  * This is a library function, which implements the writepages()
2314  * address_space_operation.
2315  */
2316 int generic_writepages(struct address_space *mapping,
2317                        struct writeback_control *wbc)
2318 {
2319         struct blk_plug plug;
2320         int ret;
2321
2322         /* deal with chardevs and other special file */
2323         if (!mapping->a_ops->writepage)
2324                 return 0;
2325
2326         blk_start_plug(&plug);
2327         ret = write_cache_pages(mapping, wbc, __writepage, mapping);
2328         blk_finish_plug(&plug);
2329         return ret;
2330 }
2331
2332 EXPORT_SYMBOL(generic_writepages);
2333
2334 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
2335 {
2336         int ret;
2337
2338         if (wbc->nr_to_write <= 0)
2339                 return 0;
2340         while (1) {
2341                 if (mapping->a_ops->writepages)
2342                         ret = mapping->a_ops->writepages(mapping, wbc);
2343                 else
2344                         ret = generic_writepages(mapping, wbc);
2345                 if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
2346                         break;
2347                 cond_resched();
2348                 congestion_wait(BLK_RW_ASYNC, HZ/50);
2349         }
2350         return ret;
2351 }
2352
2353 /**
2354  * write_one_page - write out a single page and wait on I/O
2355  * @page: the page to write
2356  *
2357  * The page must be locked by the caller and will be unlocked upon return.
2358  *
2359  * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
2360  * function returns.
2361  */
2362 int write_one_page(struct page *page)
2363 {
2364         struct address_space *mapping = page->mapping;
2365         int ret = 0;
2366         struct writeback_control wbc = {
2367                 .sync_mode = WB_SYNC_ALL,
2368                 .nr_to_write = 1,
2369         };
2370
2371         BUG_ON(!PageLocked(page));
2372
2373         wait_on_page_writeback(page);
2374
2375         if (clear_page_dirty_for_io(page)) {
2376                 get_page(page);
2377                 ret = mapping->a_ops->writepage(page, &wbc);
2378                 if (ret == 0)
2379                         wait_on_page_writeback(page);
2380                 put_page(page);
2381         } else {
2382                 unlock_page(page);
2383         }
2384
2385         if (!ret)
2386                 ret = filemap_check_errors(mapping);
2387         return ret;
2388 }
2389 EXPORT_SYMBOL(write_one_page);
2390
2391 /*
2392  * For address_spaces which do not use buffers nor write back.
2393  */
2394 int __set_page_dirty_no_writeback(struct page *page)
2395 {
2396         if (!PageDirty(page))
2397                 return !TestSetPageDirty(page);
2398         return 0;
2399 }
2400
2401 /*
2402  * Helper function for set_page_dirty family.
2403  *
2404  * Caller must hold lock_page_memcg().
2405  *
2406  * NOTE: This relies on being atomic wrt interrupts.
2407  */
2408 void account_page_dirtied(struct page *page, struct address_space *mapping)
2409 {
2410         struct inode *inode = mapping->host;
2411
2412         trace_writeback_dirty_page(page, mapping);
2413
2414         if (mapping_cap_account_dirty(mapping)) {
2415                 struct bdi_writeback *wb;
2416
2417                 inode_attach_wb(inode, page);
2418                 wb = inode_to_wb(inode);
2419
2420                 __inc_lruvec_page_state(page, NR_FILE_DIRTY);
2421                 __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2422                 __inc_node_page_state(page, NR_DIRTIED);
2423                 inc_wb_stat(wb, WB_RECLAIMABLE);
2424                 inc_wb_stat(wb, WB_DIRTIED);
2425                 task_io_account_write(PAGE_SIZE);
2426                 current->nr_dirtied++;
2427                 this_cpu_inc(bdp_ratelimits);
2428         }
2429 }
2430 EXPORT_SYMBOL(account_page_dirtied);
2431
2432 /*
2433  * Helper function for deaccounting dirty page without writeback.
2434  *
2435  * Caller must hold lock_page_memcg().
2436  */
2437 void account_page_cleaned(struct page *page, struct address_space *mapping,
2438                           struct bdi_writeback *wb)
2439 {
2440         if (mapping_cap_account_dirty(mapping)) {
2441                 dec_lruvec_page_state(page, NR_FILE_DIRTY);
2442                 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2443                 dec_wb_stat(wb, WB_RECLAIMABLE);
2444                 task_io_account_cancelled_write(PAGE_SIZE);
2445         }
2446 }
2447
2448 /*
2449  * For address_spaces which do not use buffers.  Just tag the page as dirty in
2450  * its radix tree.
2451  *
2452  * This is also used when a single buffer is being dirtied: we want to set the
2453  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
2454  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
2455  *
2456  * The caller must ensure this doesn't race with truncation.  Most will simply
2457  * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
2458  * the pte lock held, which also locks out truncation.
2459  */
2460 int __set_page_dirty_nobuffers(struct page *page)
2461 {
2462         lock_page_memcg(page);
2463         if (!TestSetPageDirty(page)) {
2464                 struct address_space *mapping = page_mapping(page);
2465                 unsigned long flags;
2466
2467                 if (!mapping) {
2468                         unlock_page_memcg(page);
2469                         return 1;
2470                 }
2471
2472                 spin_lock_irqsave(&mapping->tree_lock, flags);
2473                 BUG_ON(page_mapping(page) != mapping);
2474                 WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
2475                 account_page_dirtied(page, mapping);
2476                 radix_tree_tag_set(&mapping->page_tree, page_index(page),
2477                                    PAGECACHE_TAG_DIRTY);
2478                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2479                 unlock_page_memcg(page);
2480
2481                 if (mapping->host) {
2482                         /* !PageAnon && !swapper_space */
2483                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
2484                 }
2485                 return 1;
2486         }
2487         unlock_page_memcg(page);
2488         return 0;
2489 }
2490 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
2491
2492 /*
2493  * Call this whenever redirtying a page, to de-account the dirty counters
2494  * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
2495  * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
2496  * systematic errors in balanced_dirty_ratelimit and the dirty pages position
2497  * control.
2498  */
2499 void account_page_redirty(struct page *page)
2500 {
2501         struct address_space *mapping = page->mapping;
2502
2503         if (mapping && mapping_cap_account_dirty(mapping)) {
2504                 struct inode *inode = mapping->host;
2505                 struct bdi_writeback *wb;
2506                 bool locked;
2507
2508                 wb = unlocked_inode_to_wb_begin(inode, &locked);
2509                 current->nr_dirtied--;
2510                 dec_node_page_state(page, NR_DIRTIED);
2511                 dec_wb_stat(wb, WB_DIRTIED);
2512                 unlocked_inode_to_wb_end(inode, locked);
2513         }
2514 }
2515 EXPORT_SYMBOL(account_page_redirty);
2516
2517 /*
2518  * When a writepage implementation decides that it doesn't want to write this
2519  * page for some reason, it should redirty the locked page via
2520  * redirty_page_for_writepage() and it should then unlock the page and return 0
2521  */
2522 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
2523 {
2524         int ret;
2525
2526         wbc->pages_skipped++;
2527         ret = __set_page_dirty_nobuffers(page);
2528         account_page_redirty(page);
2529         return ret;
2530 }
2531 EXPORT_SYMBOL(redirty_page_for_writepage);
2532
2533 /*
2534  * Dirty a page.
2535  *
2536  * For pages with a mapping this should be done under the page lock
2537  * for the benefit of asynchronous memory errors who prefer a consistent
2538  * dirty state. This rule can be broken in some special cases,
2539  * but should be better not to.
2540  *
2541  * If the mapping doesn't provide a set_page_dirty a_op, then
2542  * just fall through and assume that it wants buffer_heads.
2543  */
2544 int set_page_dirty(struct page *page)
2545 {
2546         struct address_space *mapping = page_mapping(page);
2547
2548         page = compound_head(page);
2549         if (likely(mapping)) {
2550                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
2551                 /*
2552                  * readahead/lru_deactivate_page could remain
2553                  * PG_readahead/PG_reclaim due to race with end_page_writeback
2554                  * About readahead, if the page is written, the flags would be
2555                  * reset. So no problem.
2556                  * About lru_deactivate_page, if the page is redirty, the flag
2557                  * will be reset. So no problem. but if the page is used by readahead
2558                  * it will confuse readahead and make it restart the size rampup
2559                  * process. But it's a trivial problem.
2560                  */
2561                 if (PageReclaim(page))
2562                         ClearPageReclaim(page);
2563 #ifdef CONFIG_BLOCK
2564                 if (!spd)
2565                         spd = __set_page_dirty_buffers;
2566 #endif
2567                 return (*spd)(page);
2568         }
2569         if (!PageDirty(page)) {
2570                 if (!TestSetPageDirty(page))
2571                         return 1;
2572         }
2573         return 0;
2574 }
2575 EXPORT_SYMBOL(set_page_dirty);
2576
2577 /*
2578  * set_page_dirty() is racy if the caller has no reference against
2579  * page->mapping->host, and if the page is unlocked.  This is because another
2580  * CPU could truncate the page off the mapping and then free the mapping.
2581  *
2582  * Usually, the page _is_ locked, or the caller is a user-space process which
2583  * holds a reference on the inode by having an open file.
2584  *
2585  * In other cases, the page should be locked before running set_page_dirty().
2586  */
2587 int set_page_dirty_lock(struct page *page)
2588 {
2589         int ret;
2590
2591         lock_page(page);
2592         ret = set_page_dirty(page);
2593         unlock_page(page);
2594         return ret;
2595 }
2596 EXPORT_SYMBOL(set_page_dirty_lock);
2597
2598 /*
2599  * This cancels just the dirty bit on the kernel page itself, it does NOT
2600  * actually remove dirty bits on any mmap's that may be around. It also
2601  * leaves the page tagged dirty, so any sync activity will still find it on
2602  * the dirty lists, and in particular, clear_page_dirty_for_io() will still
2603  * look at the dirty bits in the VM.
2604  *
2605  * Doing this should *normally* only ever be done when a page is truncated,
2606  * and is not actually mapped anywhere at all. However, fs/buffer.c does
2607  * this when it notices that somebody has cleaned out all the buffers on a
2608  * page without actually doing it through the VM. Can you say "ext3 is
2609  * horribly ugly"? Thought you could.
2610  */
2611 void __cancel_dirty_page(struct page *page)
2612 {
2613         struct address_space *mapping = page_mapping(page);
2614
2615         if (mapping_cap_account_dirty(mapping)) {
2616                 struct inode *inode = mapping->host;
2617                 struct bdi_writeback *wb;
2618                 bool locked;
2619
2620                 lock_page_memcg(page);
2621                 wb = unlocked_inode_to_wb_begin(inode, &locked);
2622
2623                 if (TestClearPageDirty(page))
2624                         account_page_cleaned(page, mapping, wb);
2625
2626                 unlocked_inode_to_wb_end(inode, locked);
2627                 unlock_page_memcg(page);
2628         } else {
2629                 ClearPageDirty(page);
2630         }
2631 }
2632 EXPORT_SYMBOL(__cancel_dirty_page);
2633
2634 /*
2635  * Clear a page's dirty flag, while caring for dirty memory accounting.
2636  * Returns true if the page was previously dirty.
2637  *
2638  * This is for preparing to put the page under writeout.  We leave the page
2639  * tagged as dirty in the radix tree so that a concurrent write-for-sync
2640  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
2641  * implementation will run either set_page_writeback() or set_page_dirty(),
2642  * at which stage we bring the page's dirty flag and radix-tree dirty tag
2643  * back into sync.
2644  *
2645  * This incoherency between the page's dirty flag and radix-tree tag is
2646  * unfortunate, but it only exists while the page is locked.
2647  */
2648 int clear_page_dirty_for_io(struct page *page)
2649 {
2650         struct address_space *mapping = page_mapping(page);
2651         int ret = 0;
2652
2653         BUG_ON(!PageLocked(page));
2654
2655         if (mapping && mapping_cap_account_dirty(mapping)) {
2656                 struct inode *inode = mapping->host;
2657                 struct bdi_writeback *wb;
2658                 bool locked;
2659
2660                 /*
2661                  * Yes, Virginia, this is indeed insane.
2662                  *
2663                  * We use this sequence to make sure that
2664                  *  (a) we account for dirty stats properly
2665                  *  (b) we tell the low-level filesystem to
2666                  *      mark the whole page dirty if it was
2667                  *      dirty in a pagetable. Only to then
2668                  *  (c) clean the page again and return 1 to
2669                  *      cause the writeback.
2670                  *
2671                  * This way we avoid all nasty races with the
2672                  * dirty bit in multiple places and clearing
2673                  * them concurrently from different threads.
2674                  *
2675                  * Note! Normally the "set_page_dirty(page)"
2676                  * has no effect on the actual dirty bit - since
2677                  * that will already usually be set. But we
2678                  * need the side effects, and it can help us
2679                  * avoid races.
2680                  *
2681                  * We basically use the page "master dirty bit"
2682                  * as a serialization point for all the different
2683                  * threads doing their things.
2684                  */
2685                 if (page_mkclean(page))
2686                         set_page_dirty(page);
2687                 /*
2688                  * We carefully synchronise fault handlers against
2689                  * installing a dirty pte and marking the page dirty
2690                  * at this point.  We do this by having them hold the
2691                  * page lock while dirtying the page, and pages are
2692                  * always locked coming in here, so we get the desired
2693                  * exclusion.
2694                  */
2695                 wb = unlocked_inode_to_wb_begin(inode, &locked);
2696                 if (TestClearPageDirty(page)) {
2697                         dec_lruvec_page_state(page, NR_FILE_DIRTY);
2698                         dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2699                         dec_wb_stat(wb, WB_RECLAIMABLE);
2700                         ret = 1;
2701                 }
2702                 unlocked_inode_to_wb_end(inode, locked);
2703                 return ret;
2704         }
2705         return TestClearPageDirty(page);
2706 }
2707 EXPORT_SYMBOL(clear_page_dirty_for_io);
2708
2709 int test_clear_page_writeback(struct page *page)
2710 {
2711         struct address_space *mapping = page_mapping(page);
2712         struct mem_cgroup *memcg;
2713         struct lruvec *lruvec;
2714         int ret;
2715
2716         memcg = lock_page_memcg(page);
2717         lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
2718         if (mapping && mapping_use_writeback_tags(mapping)) {
2719                 struct inode *inode = mapping->host;
2720                 struct backing_dev_info *bdi = inode_to_bdi(inode);
2721                 unsigned long flags;
2722
2723                 spin_lock_irqsave(&mapping->tree_lock, flags);
2724                 ret = TestClearPageWriteback(page);
2725                 if (ret) {
2726                         radix_tree_tag_clear(&mapping->page_tree,
2727                                                 page_index(page),
2728                                                 PAGECACHE_TAG_WRITEBACK);
2729                         if (bdi_cap_account_writeback(bdi)) {
2730                                 struct bdi_writeback *wb = inode_to_wb(inode);
2731
2732                                 dec_wb_stat(wb, WB_WRITEBACK);
2733                                 __wb_writeout_inc(wb);
2734                         }
2735                 }
2736
2737                 if (mapping->host && !mapping_tagged(mapping,
2738                                                      PAGECACHE_TAG_WRITEBACK))
2739                         sb_clear_inode_writeback(mapping->host);
2740
2741                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2742         } else {
2743                 ret = TestClearPageWriteback(page);
2744         }
2745         /*
2746          * NOTE: Page might be free now! Writeback doesn't hold a page
2747          * reference on its own, it relies on truncation to wait for
2748          * the clearing of PG_writeback. The below can only access
2749          * page state that is static across allocation cycles.
2750          */
2751         if (ret) {
2752                 dec_lruvec_state(lruvec, NR_WRITEBACK);
2753                 dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2754                 inc_node_page_state(page, NR_WRITTEN);
2755         }
2756         __unlock_page_memcg(memcg);
2757         return ret;
2758 }
2759
2760 int __test_set_page_writeback(struct page *page, bool keep_write)
2761 {
2762         struct address_space *mapping = page_mapping(page);
2763         int ret;
2764
2765         lock_page_memcg(page);
2766         if (mapping && mapping_use_writeback_tags(mapping)) {
2767                 struct inode *inode = mapping->host;
2768                 struct backing_dev_info *bdi = inode_to_bdi(inode);
2769                 unsigned long flags;
2770
2771                 spin_lock_irqsave(&mapping->tree_lock, flags);
2772                 ret = TestSetPageWriteback(page);
2773                 if (!ret) {
2774                         bool on_wblist;
2775
2776                         on_wblist = mapping_tagged(mapping,
2777                                                    PAGECACHE_TAG_WRITEBACK);
2778
2779                         radix_tree_tag_set(&mapping->page_tree,
2780                                                 page_index(page),
2781                                                 PAGECACHE_TAG_WRITEBACK);
2782                         if (bdi_cap_account_writeback(bdi))
2783                                 inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
2784
2785                         /*
2786                          * We can come through here when swapping anonymous
2787                          * pages, so we don't necessarily have an inode to track
2788                          * for sync.
2789                          */
2790                         if (mapping->host && !on_wblist)
2791                                 sb_mark_inode_writeback(mapping->host);
2792                 }
2793                 if (!PageDirty(page))
2794                         radix_tree_tag_clear(&mapping->page_tree,
2795                                                 page_index(page),
2796                                                 PAGECACHE_TAG_DIRTY);
2797                 if (!keep_write)
2798                         radix_tree_tag_clear(&mapping->page_tree,
2799                                                 page_index(page),
2800                                                 PAGECACHE_TAG_TOWRITE);
2801                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
2802         } else {
2803                 ret = TestSetPageWriteback(page);
2804         }
2805         if (!ret) {
2806                 inc_lruvec_page_state(page, NR_WRITEBACK);
2807                 inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
2808         }
2809         unlock_page_memcg(page);
2810         return ret;
2811
2812 }
2813 EXPORT_SYMBOL(__test_set_page_writeback);
2814
2815 /*
2816  * Return true if any of the pages in the mapping are marked with the
2817  * passed tag.
2818  */
2819 int mapping_tagged(struct address_space *mapping, int tag)
2820 {
2821         return radix_tree_tagged(&mapping->page_tree, tag);
2822 }
2823 EXPORT_SYMBOL(mapping_tagged);
2824
2825 /**
2826  * wait_for_stable_page() - wait for writeback to finish, if necessary.
2827  * @page:       The page to wait on.
2828  *
2829  * This function determines if the given page is related to a backing device
2830  * that requires page contents to be held stable during writeback.  If so, then
2831  * it will wait for any pending writeback to complete.
2832  */
2833 void wait_for_stable_page(struct page *page)
2834 {
2835         if (bdi_cap_stable_pages_required(inode_to_bdi(page->mapping->host)))
2836                 wait_on_page_writeback(page);
2837 }
2838 EXPORT_SYMBOL_GPL(wait_for_stable_page);