eceaf496210fcf241d55482e9dd317c2a9d5dc56
[sfrench/cifs-2.6.git] / mm / vmstat.c
1 /*
2  *  linux/mm/vmstat.c
3  *
4  *  Manages VM statistics
5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
6  *
7  *  zoned VM statistics
8  *  Copyright (C) 2006 Silicon Graphics, Inc.,
9  *              Christoph Lameter <christoph@lameter.com>
10  */
11
12 #include <linux/mm.h>
13 #include <linux/module.h>
14 #include <linux/cpu.h>
15 #include <linux/sched.h>
16
17 #ifdef CONFIG_VM_EVENT_COUNTERS
18 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
19 EXPORT_PER_CPU_SYMBOL(vm_event_states);
20
21 static void sum_vm_events(unsigned long *ret, cpumask_t *cpumask)
22 {
23         int cpu = 0;
24         int i;
25
26         memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));
27
28         cpu = first_cpu(*cpumask);
29         while (cpu < NR_CPUS) {
30                 struct vm_event_state *this = &per_cpu(vm_event_states, cpu);
31
32                 cpu = next_cpu(cpu, *cpumask);
33
34                 if (cpu < NR_CPUS)
35                         prefetch(&per_cpu(vm_event_states, cpu));
36
37
38                 for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
39                         ret[i] += this->event[i];
40         }
41 }
42
43 /*
44  * Accumulate the vm event counters across all CPUs.
45  * The result is unavoidably approximate - it can change
46  * during and after execution of this function.
47 */
48 void all_vm_events(unsigned long *ret)
49 {
50         sum_vm_events(ret, &cpu_online_map);
51 }
52 EXPORT_SYMBOL_GPL(all_vm_events);
53
54 #ifdef CONFIG_HOTPLUG
55 /*
56  * Fold the foreign cpu events into our own.
57  *
58  * This is adding to the events on one processor
59  * but keeps the global counts constant.
60  */
61 void vm_events_fold_cpu(int cpu)
62 {
63         struct vm_event_state *fold_state = &per_cpu(vm_event_states, cpu);
64         int i;
65
66         for (i = 0; i < NR_VM_EVENT_ITEMS; i++) {
67                 count_vm_events(i, fold_state->event[i]);
68                 fold_state->event[i] = 0;
69         }
70 }
71 #endif /* CONFIG_HOTPLUG */
72
73 #endif /* CONFIG_VM_EVENT_COUNTERS */
74
75 /*
76  * Manage combined zone based / global counters
77  *
78  * vm_stat contains the global counters
79  */
80 atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
81 EXPORT_SYMBOL(vm_stat);
82
83 #ifdef CONFIG_SMP
84
85 static int calculate_threshold(struct zone *zone)
86 {
87         int threshold;
88         int mem;        /* memory in 128 MB units */
89
90         /*
91          * The threshold scales with the number of processors and the amount
92          * of memory per zone. More memory means that we can defer updates for
93          * longer, more processors could lead to more contention.
94          * fls() is used to have a cheap way of logarithmic scaling.
95          *
96          * Some sample thresholds:
97          *
98          * Threshold    Processors      (fls)   Zonesize        fls(mem+1)
99          * ------------------------------------------------------------------
100          * 8            1               1       0.9-1 GB        4
101          * 16           2               2       0.9-1 GB        4
102          * 20           2               2       1-2 GB          5
103          * 24           2               2       2-4 GB          6
104          * 28           2               2       4-8 GB          7
105          * 32           2               2       8-16 GB         8
106          * 4            2               2       <128M           1
107          * 30           4               3       2-4 GB          5
108          * 48           4               3       8-16 GB         8
109          * 32           8               4       1-2 GB          4
110          * 32           8               4       0.9-1GB         4
111          * 10           16              5       <128M           1
112          * 40           16              5       900M            4
113          * 70           64              7       2-4 GB          5
114          * 84           64              7       4-8 GB          6
115          * 108          512             9       4-8 GB          6
116          * 125          1024            10      8-16 GB         8
117          * 125          1024            10      16-32 GB        9
118          */
119
120         mem = zone->present_pages >> (27 - PAGE_SHIFT);
121
122         threshold = 2 * fls(num_online_cpus()) * (1 + fls(mem));
123
124         /*
125          * Maximum threshold is 125
126          */
127         threshold = min(125, threshold);
128
129         return threshold;
130 }
131
132 /*
133  * Refresh the thresholds for each zone.
134  */
135 static void refresh_zone_stat_thresholds(void)
136 {
137         struct zone *zone;
138         int cpu;
139         int threshold;
140
141         for_each_zone(zone) {
142
143                 if (!zone->present_pages)
144                         continue;
145
146                 threshold = calculate_threshold(zone);
147
148                 for_each_online_cpu(cpu)
149                         zone_pcp(zone, cpu)->stat_threshold = threshold;
150         }
151 }
152
153 /*
154  * For use when we know that interrupts are disabled.
155  */
156 void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
157                                 int delta)
158 {
159         struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
160         s8 *p = pcp->vm_stat_diff + item;
161         long x;
162
163         x = delta + *p;
164
165         if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
166                 zone_page_state_add(x, zone, item);
167                 x = 0;
168         }
169         *p = x;
170 }
171 EXPORT_SYMBOL(__mod_zone_page_state);
172
173 /*
174  * For an unknown interrupt state
175  */
176 void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
177                                         int delta)
178 {
179         unsigned long flags;
180
181         local_irq_save(flags);
182         __mod_zone_page_state(zone, item, delta);
183         local_irq_restore(flags);
184 }
185 EXPORT_SYMBOL(mod_zone_page_state);
186
187 /*
188  * Optimized increment and decrement functions.
189  *
190  * These are only for a single page and therefore can take a struct page *
191  * argument instead of struct zone *. This allows the inclusion of the code
192  * generated for page_zone(page) into the optimized functions.
193  *
194  * No overflow check is necessary and therefore the differential can be
195  * incremented or decremented in place which may allow the compilers to
196  * generate better code.
197  * The increment or decrement is known and therefore one boundary check can
198  * be omitted.
199  *
200  * NOTE: These functions are very performance sensitive. Change only
201  * with care.
202  *
203  * Some processors have inc/dec instructions that are atomic vs an interrupt.
204  * However, the code must first determine the differential location in a zone
205  * based on the processor number and then inc/dec the counter. There is no
206  * guarantee without disabling preemption that the processor will not change
207  * in between and therefore the atomicity vs. interrupt cannot be exploited
208  * in a useful way here.
209  */
210 void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
211 {
212         struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
213         s8 *p = pcp->vm_stat_diff + item;
214
215         (*p)++;
216
217         if (unlikely(*p > pcp->stat_threshold)) {
218                 int overstep = pcp->stat_threshold / 2;
219
220                 zone_page_state_add(*p + overstep, zone, item);
221                 *p = -overstep;
222         }
223 }
224
225 void __inc_zone_page_state(struct page *page, enum zone_stat_item item)
226 {
227         __inc_zone_state(page_zone(page), item);
228 }
229 EXPORT_SYMBOL(__inc_zone_page_state);
230
231 void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
232 {
233         struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
234         s8 *p = pcp->vm_stat_diff + item;
235
236         (*p)--;
237
238         if (unlikely(*p < - pcp->stat_threshold)) {
239                 int overstep = pcp->stat_threshold / 2;
240
241                 zone_page_state_add(*p - overstep, zone, item);
242                 *p = overstep;
243         }
244 }
245
246 void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
247 {
248         __dec_zone_state(page_zone(page), item);
249 }
250 EXPORT_SYMBOL(__dec_zone_page_state);
251
252 void inc_zone_state(struct zone *zone, enum zone_stat_item item)
253 {
254         unsigned long flags;
255
256         local_irq_save(flags);
257         __inc_zone_state(zone, item);
258         local_irq_restore(flags);
259 }
260
261 void inc_zone_page_state(struct page *page, enum zone_stat_item item)
262 {
263         unsigned long flags;
264         struct zone *zone;
265
266         zone = page_zone(page);
267         local_irq_save(flags);
268         __inc_zone_state(zone, item);
269         local_irq_restore(flags);
270 }
271 EXPORT_SYMBOL(inc_zone_page_state);
272
273 void dec_zone_page_state(struct page *page, enum zone_stat_item item)
274 {
275         unsigned long flags;
276
277         local_irq_save(flags);
278         __dec_zone_page_state(page, item);
279         local_irq_restore(flags);
280 }
281 EXPORT_SYMBOL(dec_zone_page_state);
282
283 /*
284  * Update the zone counters for one cpu.
285  *
286  * Note that refresh_cpu_vm_stats strives to only access
287  * node local memory. The per cpu pagesets on remote zones are placed
288  * in the memory local to the processor using that pageset. So the
289  * loop over all zones will access a series of cachelines local to
290  * the processor.
291  *
292  * The call to zone_page_state_add updates the cachelines with the
293  * statistics in the remote zone struct as well as the global cachelines
294  * with the global counters. These could cause remote node cache line
295  * bouncing and will have to be only done when necessary.
296  */
297 void refresh_cpu_vm_stats(int cpu)
298 {
299         struct zone *zone;
300         int i;
301         unsigned long flags;
302
303         for_each_zone(zone) {
304                 struct per_cpu_pageset *p;
305
306                 if (!populated_zone(zone))
307                         continue;
308
309                 p = zone_pcp(zone, cpu);
310
311                 for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
312                         if (p->vm_stat_diff[i]) {
313                                 local_irq_save(flags);
314                                 zone_page_state_add(p->vm_stat_diff[i],
315                                         zone, i);
316                                 p->vm_stat_diff[i] = 0;
317 #ifdef CONFIG_NUMA
318                                 /* 3 seconds idle till flush */
319                                 p->expire = 3;
320 #endif
321                                 local_irq_restore(flags);
322                         }
323 #ifdef CONFIG_NUMA
324                 /*
325                  * Deal with draining the remote pageset of this
326                  * processor
327                  *
328                  * Check if there are pages remaining in this pageset
329                  * if not then there is nothing to expire.
330                  */
331                 if (!p->expire || (!p->pcp[0].count && !p->pcp[1].count))
332                         continue;
333
334                 /*
335                  * We never drain zones local to this processor.
336                  */
337                 if (zone_to_nid(zone) == numa_node_id()) {
338                         p->expire = 0;
339                         continue;
340                 }
341
342                 p->expire--;
343                 if (p->expire)
344                         continue;
345
346                 if (p->pcp[0].count)
347                         drain_zone_pages(zone, p->pcp + 0);
348
349                 if (p->pcp[1].count)
350                         drain_zone_pages(zone, p->pcp + 1);
351 #endif
352         }
353 }
354
355 static void __refresh_cpu_vm_stats(void *dummy)
356 {
357         refresh_cpu_vm_stats(smp_processor_id());
358 }
359
360 /*
361  * Consolidate all counters.
362  *
363  * Note that the result is less inaccurate but still inaccurate
364  * if concurrent processes are allowed to run.
365  */
366 void refresh_vm_stats(void)
367 {
368         on_each_cpu(__refresh_cpu_vm_stats, NULL, 0, 1);
369 }
370 EXPORT_SYMBOL(refresh_vm_stats);
371
372 #endif
373
374 #ifdef CONFIG_NUMA
375 /*
376  * zonelist = the list of zones passed to the allocator
377  * z        = the zone from which the allocation occurred.
378  *
379  * Must be called with interrupts disabled.
380  */
381 void zone_statistics(struct zonelist *zonelist, struct zone *z)
382 {
383         if (z->zone_pgdat == zonelist->zones[0]->zone_pgdat) {
384                 __inc_zone_state(z, NUMA_HIT);
385         } else {
386                 __inc_zone_state(z, NUMA_MISS);
387                 __inc_zone_state(zonelist->zones[0], NUMA_FOREIGN);
388         }
389         if (z->node == numa_node_id())
390                 __inc_zone_state(z, NUMA_LOCAL);
391         else
392                 __inc_zone_state(z, NUMA_OTHER);
393 }
394 #endif
395
396 #ifdef CONFIG_PROC_FS
397
398 #include <linux/seq_file.h>
399
400 static void *frag_start(struct seq_file *m, loff_t *pos)
401 {
402         pg_data_t *pgdat;
403         loff_t node = *pos;
404         for (pgdat = first_online_pgdat();
405              pgdat && node;
406              pgdat = next_online_pgdat(pgdat))
407                 --node;
408
409         return pgdat;
410 }
411
412 static void *frag_next(struct seq_file *m, void *arg, loff_t *pos)
413 {
414         pg_data_t *pgdat = (pg_data_t *)arg;
415
416         (*pos)++;
417         return next_online_pgdat(pgdat);
418 }
419
420 static void frag_stop(struct seq_file *m, void *arg)
421 {
422 }
423
424 /*
425  * This walks the free areas for each zone.
426  */
427 static int frag_show(struct seq_file *m, void *arg)
428 {
429         pg_data_t *pgdat = (pg_data_t *)arg;
430         struct zone *zone;
431         struct zone *node_zones = pgdat->node_zones;
432         unsigned long flags;
433         int order;
434
435         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
436                 if (!populated_zone(zone))
437                         continue;
438
439                 spin_lock_irqsave(&zone->lock, flags);
440                 seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
441                 for (order = 0; order < MAX_ORDER; ++order)
442                         seq_printf(m, "%6lu ", zone->free_area[order].nr_free);
443                 spin_unlock_irqrestore(&zone->lock, flags);
444                 seq_putc(m, '\n');
445         }
446         return 0;
447 }
448
449 const struct seq_operations fragmentation_op = {
450         .start  = frag_start,
451         .next   = frag_next,
452         .stop   = frag_stop,
453         .show   = frag_show,
454 };
455
456 #ifdef CONFIG_ZONE_DMA
457 #define TEXT_FOR_DMA(xx) xx "_dma",
458 #else
459 #define TEXT_FOR_DMA(xx)
460 #endif
461
462 #ifdef CONFIG_ZONE_DMA32
463 #define TEXT_FOR_DMA32(xx) xx "_dma32",
464 #else
465 #define TEXT_FOR_DMA32(xx)
466 #endif
467
468 #ifdef CONFIG_HIGHMEM
469 #define TEXT_FOR_HIGHMEM(xx) xx "_high",
470 #else
471 #define TEXT_FOR_HIGHMEM(xx)
472 #endif
473
474 #define TEXTS_FOR_ZONES(xx) TEXT_FOR_DMA(xx) TEXT_FOR_DMA32(xx) xx "_normal", \
475                                         TEXT_FOR_HIGHMEM(xx)
476
477 static const char * const vmstat_text[] = {
478         /* Zoned VM counters */
479         "nr_free_pages",
480         "nr_inactive",
481         "nr_active",
482         "nr_anon_pages",
483         "nr_mapped",
484         "nr_file_pages",
485         "nr_dirty",
486         "nr_writeback",
487         "nr_slab_reclaimable",
488         "nr_slab_unreclaimable",
489         "nr_page_table_pages",
490         "nr_unstable",
491         "nr_bounce",
492         "nr_vmscan_write",
493
494 #ifdef CONFIG_NUMA
495         "numa_hit",
496         "numa_miss",
497         "numa_foreign",
498         "numa_interleave",
499         "numa_local",
500         "numa_other",
501 #endif
502
503 #ifdef CONFIG_VM_EVENT_COUNTERS
504         "pgpgin",
505         "pgpgout",
506         "pswpin",
507         "pswpout",
508
509         TEXTS_FOR_ZONES("pgalloc")
510
511         "pgfree",
512         "pgactivate",
513         "pgdeactivate",
514
515         "pgfault",
516         "pgmajfault",
517
518         TEXTS_FOR_ZONES("pgrefill")
519         TEXTS_FOR_ZONES("pgsteal")
520         TEXTS_FOR_ZONES("pgscan_kswapd")
521         TEXTS_FOR_ZONES("pgscan_direct")
522
523         "pginodesteal",
524         "slabs_scanned",
525         "kswapd_steal",
526         "kswapd_inodesteal",
527         "pageoutrun",
528         "allocstall",
529
530         "pgrotated",
531 #endif
532 };
533
534 /*
535  * Output information about zones in @pgdat.
536  */
537 static int zoneinfo_show(struct seq_file *m, void *arg)
538 {
539         pg_data_t *pgdat = arg;
540         struct zone *zone;
541         struct zone *node_zones = pgdat->node_zones;
542         unsigned long flags;
543
544         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; zone++) {
545                 int i;
546
547                 if (!populated_zone(zone))
548                         continue;
549
550                 spin_lock_irqsave(&zone->lock, flags);
551                 seq_printf(m, "Node %d, zone %8s", pgdat->node_id, zone->name);
552                 seq_printf(m,
553                            "\n  pages free     %lu"
554                            "\n        min      %lu"
555                            "\n        low      %lu"
556                            "\n        high     %lu"
557                            "\n        scanned  %lu (a: %lu i: %lu)"
558                            "\n        spanned  %lu"
559                            "\n        present  %lu",
560                            zone_page_state(zone, NR_FREE_PAGES),
561                            zone->pages_min,
562                            zone->pages_low,
563                            zone->pages_high,
564                            zone->pages_scanned,
565                            zone->nr_scan_active, zone->nr_scan_inactive,
566                            zone->spanned_pages,
567                            zone->present_pages);
568
569                 for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
570                         seq_printf(m, "\n    %-12s %lu", vmstat_text[i],
571                                         zone_page_state(zone, i));
572
573                 seq_printf(m,
574                            "\n        protection: (%lu",
575                            zone->lowmem_reserve[0]);
576                 for (i = 1; i < ARRAY_SIZE(zone->lowmem_reserve); i++)
577                         seq_printf(m, ", %lu", zone->lowmem_reserve[i]);
578                 seq_printf(m,
579                            ")"
580                            "\n  pagesets");
581                 for_each_online_cpu(i) {
582                         struct per_cpu_pageset *pageset;
583                         int j;
584
585                         pageset = zone_pcp(zone, i);
586                         for (j = 0; j < ARRAY_SIZE(pageset->pcp); j++) {
587                                 seq_printf(m,
588                                            "\n    cpu: %i pcp: %i"
589                                            "\n              count: %i"
590                                            "\n              high:  %i"
591                                            "\n              batch: %i",
592                                            i, j,
593                                            pageset->pcp[j].count,
594                                            pageset->pcp[j].high,
595                                            pageset->pcp[j].batch);
596                         }
597 #ifdef CONFIG_SMP
598                         seq_printf(m, "\n  vm stats threshold: %d",
599                                         pageset->stat_threshold);
600 #endif
601                 }
602                 seq_printf(m,
603                            "\n  all_unreclaimable: %u"
604                            "\n  prev_priority:     %i"
605                            "\n  start_pfn:         %lu",
606                            zone->all_unreclaimable,
607                            zone->prev_priority,
608                            zone->zone_start_pfn);
609                 spin_unlock_irqrestore(&zone->lock, flags);
610                 seq_putc(m, '\n');
611         }
612         return 0;
613 }
614
615 const struct seq_operations zoneinfo_op = {
616         .start  = frag_start, /* iterate over all zones. The same as in
617                                * fragmentation. */
618         .next   = frag_next,
619         .stop   = frag_stop,
620         .show   = zoneinfo_show,
621 };
622
623 static void *vmstat_start(struct seq_file *m, loff_t *pos)
624 {
625         unsigned long *v;
626 #ifdef CONFIG_VM_EVENT_COUNTERS
627         unsigned long *e;
628 #endif
629         int i;
630
631         if (*pos >= ARRAY_SIZE(vmstat_text))
632                 return NULL;
633
634 #ifdef CONFIG_VM_EVENT_COUNTERS
635         v = kmalloc(NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long)
636                         + sizeof(struct vm_event_state), GFP_KERNEL);
637 #else
638         v = kmalloc(NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long),
639                         GFP_KERNEL);
640 #endif
641         m->private = v;
642         if (!v)
643                 return ERR_PTR(-ENOMEM);
644         for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
645                 v[i] = global_page_state(i);
646 #ifdef CONFIG_VM_EVENT_COUNTERS
647         e = v + NR_VM_ZONE_STAT_ITEMS;
648         all_vm_events(e);
649         e[PGPGIN] /= 2;         /* sectors -> kbytes */
650         e[PGPGOUT] /= 2;
651 #endif
652         return v + *pos;
653 }
654
655 static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos)
656 {
657         (*pos)++;
658         if (*pos >= ARRAY_SIZE(vmstat_text))
659                 return NULL;
660         return (unsigned long *)m->private + *pos;
661 }
662
663 static int vmstat_show(struct seq_file *m, void *arg)
664 {
665         unsigned long *l = arg;
666         unsigned long off = l - (unsigned long *)m->private;
667
668         seq_printf(m, "%s %lu\n", vmstat_text[off], *l);
669         return 0;
670 }
671
672 static void vmstat_stop(struct seq_file *m, void *arg)
673 {
674         kfree(m->private);
675         m->private = NULL;
676 }
677
678 const struct seq_operations vmstat_op = {
679         .start  = vmstat_start,
680         .next   = vmstat_next,
681         .stop   = vmstat_stop,
682         .show   = vmstat_show,
683 };
684
685 #endif /* CONFIG_PROC_FS */
686
687 #ifdef CONFIG_SMP
688 static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
689 int sysctl_stat_interval __read_mostly = HZ;
690
691 static void vmstat_update(struct work_struct *w)
692 {
693         refresh_cpu_vm_stats(smp_processor_id());
694         schedule_delayed_work(&__get_cpu_var(vmstat_work),
695                 sysctl_stat_interval);
696 }
697
698 static void __devinit start_cpu_timer(int cpu)
699 {
700         struct delayed_work *vmstat_work = &per_cpu(vmstat_work, cpu);
701
702         INIT_DELAYED_WORK_DEFERRABLE(vmstat_work, vmstat_update);
703         schedule_delayed_work_on(cpu, vmstat_work, HZ + cpu);
704 }
705
706 /*
707  * Use the cpu notifier to insure that the thresholds are recalculated
708  * when necessary.
709  */
710 static int __cpuinit vmstat_cpuup_callback(struct notifier_block *nfb,
711                 unsigned long action,
712                 void *hcpu)
713 {
714         long cpu = (long)hcpu;
715
716         switch (action) {
717         case CPU_ONLINE:
718         case CPU_ONLINE_FROZEN:
719                 start_cpu_timer(cpu);
720                 break;
721         case CPU_DOWN_PREPARE:
722         case CPU_DOWN_PREPARE_FROZEN:
723                 cancel_rearming_delayed_work(&per_cpu(vmstat_work, cpu));
724                 per_cpu(vmstat_work, cpu).work.func = NULL;
725                 break;
726         case CPU_DOWN_FAILED:
727         case CPU_DOWN_FAILED_FROZEN:
728                 start_cpu_timer(cpu);
729                 break;
730         case CPU_DEAD:
731         case CPU_DEAD_FROZEN:
732                 refresh_zone_stat_thresholds();
733                 break;
734         default:
735                 break;
736         }
737         return NOTIFY_OK;
738 }
739
740 static struct notifier_block __cpuinitdata vmstat_notifier =
741         { &vmstat_cpuup_callback, NULL, 0 };
742
743 int __init setup_vmstat(void)
744 {
745         int cpu;
746
747         refresh_zone_stat_thresholds();
748         register_cpu_notifier(&vmstat_notifier);
749
750         for_each_online_cpu(cpu)
751                 start_cpu_timer(cpu);
752         return 0;
753 }
754 module_init(setup_vmstat)
755 #endif