be8f8d36a8b9b6919f4d1c36e1b3b3e973b242f1
[sfrench/cifs-2.6.git] / mm / highmem.c
1 /*
2  * High memory handling common code and variables.
3  *
4  * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
5  *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
6  *
7  *
8  * Redesigned the x86 32-bit VM architecture to deal with
9  * 64-bit physical space. With current x86 CPUs this
10  * means up to 64 Gigabytes physical RAM.
11  *
12  * Rewrote high memory support to move the page cache into
13  * high memory. Implemented permanent (schedulable) kmaps
14  * based on Linus' idea.
15  *
16  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
17  */
18
19 #include <linux/mm.h>
20 #include <linux/module.h>
21 #include <linux/swap.h>
22 #include <linux/bio.h>
23 #include <linux/pagemap.h>
24 #include <linux/mempool.h>
25 #include <linux/blkdev.h>
26 #include <linux/init.h>
27 #include <linux/hash.h>
28 #include <linux/highmem.h>
29 #include <linux/blktrace_api.h>
30 #include <asm/tlbflush.h>
31
32 /*
33  * Virtual_count is not a pure "count".
34  *  0 means that it is not mapped, and has not been mapped
35  *    since a TLB flush - it is usable.
36  *  1 means that there are no users, but it has been mapped
37  *    since the last TLB flush - so we can't use it.
38  *  n means that there are (n-1) current users of it.
39  */
40 #ifdef CONFIG_HIGHMEM
41
42 unsigned long totalhigh_pages __read_mostly;
43
44 unsigned int nr_free_highpages (void)
45 {
46         pg_data_t *pgdat;
47         unsigned int pages = 0;
48
49         for_each_online_pgdat(pgdat)
50                 pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
51                         NR_FREE_PAGES);
52
53         return pages;
54 }
55
56 static int pkmap_count[LAST_PKMAP];
57 static unsigned int last_pkmap_nr;
58 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
59
60 pte_t * pkmap_page_table;
61
62 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
63
64 static void flush_all_zero_pkmaps(void)
65 {
66         int i;
67
68         flush_cache_kmaps();
69
70         for (i = 0; i < LAST_PKMAP; i++) {
71                 struct page *page;
72
73                 /*
74                  * zero means we don't have anything to do,
75                  * >1 means that it is still in use. Only
76                  * a count of 1 means that it is free but
77                  * needs to be unmapped
78                  */
79                 if (pkmap_count[i] != 1)
80                         continue;
81                 pkmap_count[i] = 0;
82
83                 /* sanity check */
84                 BUG_ON(pte_none(pkmap_page_table[i]));
85
86                 /*
87                  * Don't need an atomic fetch-and-clear op here;
88                  * no-one has the page mapped, and cannot get at
89                  * its virtual address (and hence PTE) without first
90                  * getting the kmap_lock (which is held here).
91                  * So no dangers, even with speculative execution.
92                  */
93                 page = pte_page(pkmap_page_table[i]);
94                 pte_clear(&init_mm, (unsigned long)page_address(page),
95                           &pkmap_page_table[i]);
96
97                 set_page_address(page, NULL);
98         }
99         flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
100 }
101
102 /* Flush all unused kmap mappings in order to remove stray
103    mappings. */
104 void kmap_flush_unused(void)
105 {
106         spin_lock(&kmap_lock);
107         flush_all_zero_pkmaps();
108         spin_unlock(&kmap_lock);
109 }
110
111 static inline unsigned long map_new_virtual(struct page *page)
112 {
113         unsigned long vaddr;
114         int count;
115
116 start:
117         count = LAST_PKMAP;
118         /* Find an empty entry */
119         for (;;) {
120                 last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
121                 if (!last_pkmap_nr) {
122                         flush_all_zero_pkmaps();
123                         count = LAST_PKMAP;
124                 }
125                 if (!pkmap_count[last_pkmap_nr])
126                         break;  /* Found a usable entry */
127                 if (--count)
128                         continue;
129
130                 /*
131                  * Sleep for somebody else to unmap their entries
132                  */
133                 {
134                         DECLARE_WAITQUEUE(wait, current);
135
136                         __set_current_state(TASK_UNINTERRUPTIBLE);
137                         add_wait_queue(&pkmap_map_wait, &wait);
138                         spin_unlock(&kmap_lock);
139                         schedule();
140                         remove_wait_queue(&pkmap_map_wait, &wait);
141                         spin_lock(&kmap_lock);
142
143                         /* Somebody else might have mapped it while we slept */
144                         if (page_address(page))
145                                 return (unsigned long)page_address(page);
146
147                         /* Re-start */
148                         goto start;
149                 }
150         }
151         vaddr = PKMAP_ADDR(last_pkmap_nr);
152         set_pte_at(&init_mm, vaddr,
153                    &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
154
155         pkmap_count[last_pkmap_nr] = 1;
156         set_page_address(page, (void *)vaddr);
157
158         return vaddr;
159 }
160
161 void fastcall *kmap_high(struct page *page)
162 {
163         unsigned long vaddr;
164
165         /*
166          * For highmem pages, we can't trust "virtual" until
167          * after we have the lock.
168          *
169          * We cannot call this from interrupts, as it may block
170          */
171         spin_lock(&kmap_lock);
172         vaddr = (unsigned long)page_address(page);
173         if (!vaddr)
174                 vaddr = map_new_virtual(page);
175         pkmap_count[PKMAP_NR(vaddr)]++;
176         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
177         spin_unlock(&kmap_lock);
178         return (void*) vaddr;
179 }
180
181 EXPORT_SYMBOL(kmap_high);
182
183 void fastcall kunmap_high(struct page *page)
184 {
185         unsigned long vaddr;
186         unsigned long nr;
187         int need_wakeup;
188
189         spin_lock(&kmap_lock);
190         vaddr = (unsigned long)page_address(page);
191         BUG_ON(!vaddr);
192         nr = PKMAP_NR(vaddr);
193
194         /*
195          * A count must never go down to zero
196          * without a TLB flush!
197          */
198         need_wakeup = 0;
199         switch (--pkmap_count[nr]) {
200         case 0:
201                 BUG();
202         case 1:
203                 /*
204                  * Avoid an unnecessary wake_up() function call.
205                  * The common case is pkmap_count[] == 1, but
206                  * no waiters.
207                  * The tasks queued in the wait-queue are guarded
208                  * by both the lock in the wait-queue-head and by
209                  * the kmap_lock.  As the kmap_lock is held here,
210                  * no need for the wait-queue-head's lock.  Simply
211                  * test if the queue is empty.
212                  */
213                 need_wakeup = waitqueue_active(&pkmap_map_wait);
214         }
215         spin_unlock(&kmap_lock);
216
217         /* do wake-up, if needed, race-free outside of the spin lock */
218         if (need_wakeup)
219                 wake_up(&pkmap_map_wait);
220 }
221
222 EXPORT_SYMBOL(kunmap_high);
223 #endif
224
225 #if defined(HASHED_PAGE_VIRTUAL)
226
227 #define PA_HASH_ORDER   7
228
229 /*
230  * Describes one page->virtual association
231  */
232 struct page_address_map {
233         struct page *page;
234         void *virtual;
235         struct list_head list;
236 };
237
238 /*
239  * page_address_map freelist, allocated from page_address_maps.
240  */
241 static struct list_head page_address_pool;      /* freelist */
242 static spinlock_t pool_lock;                    /* protects page_address_pool */
243
244 /*
245  * Hash table bucket
246  */
247 static struct page_address_slot {
248         struct list_head lh;                    /* List of page_address_maps */
249         spinlock_t lock;                        /* Protect this bucket's list */
250 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
251
252 static struct page_address_slot *page_slot(struct page *page)
253 {
254         return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
255 }
256
257 void *page_address(struct page *page)
258 {
259         unsigned long flags;
260         void *ret;
261         struct page_address_slot *pas;
262
263         if (!PageHighMem(page))
264                 return lowmem_page_address(page);
265
266         pas = page_slot(page);
267         ret = NULL;
268         spin_lock_irqsave(&pas->lock, flags);
269         if (!list_empty(&pas->lh)) {
270                 struct page_address_map *pam;
271
272                 list_for_each_entry(pam, &pas->lh, list) {
273                         if (pam->page == page) {
274                                 ret = pam->virtual;
275                                 goto done;
276                         }
277                 }
278         }
279 done:
280         spin_unlock_irqrestore(&pas->lock, flags);
281         return ret;
282 }
283
284 EXPORT_SYMBOL(page_address);
285
286 void set_page_address(struct page *page, void *virtual)
287 {
288         unsigned long flags;
289         struct page_address_slot *pas;
290         struct page_address_map *pam;
291
292         BUG_ON(!PageHighMem(page));
293
294         pas = page_slot(page);
295         if (virtual) {          /* Add */
296                 BUG_ON(list_empty(&page_address_pool));
297
298                 spin_lock_irqsave(&pool_lock, flags);
299                 pam = list_entry(page_address_pool.next,
300                                 struct page_address_map, list);
301                 list_del(&pam->list);
302                 spin_unlock_irqrestore(&pool_lock, flags);
303
304                 pam->page = page;
305                 pam->virtual = virtual;
306
307                 spin_lock_irqsave(&pas->lock, flags);
308                 list_add_tail(&pam->list, &pas->lh);
309                 spin_unlock_irqrestore(&pas->lock, flags);
310         } else {                /* Remove */
311                 spin_lock_irqsave(&pas->lock, flags);
312                 list_for_each_entry(pam, &pas->lh, list) {
313                         if (pam->page == page) {
314                                 list_del(&pam->list);
315                                 spin_unlock_irqrestore(&pas->lock, flags);
316                                 spin_lock_irqsave(&pool_lock, flags);
317                                 list_add_tail(&pam->list, &page_address_pool);
318                                 spin_unlock_irqrestore(&pool_lock, flags);
319                                 goto done;
320                         }
321                 }
322                 spin_unlock_irqrestore(&pas->lock, flags);
323         }
324 done:
325         return;
326 }
327
328 static struct page_address_map page_address_maps[LAST_PKMAP];
329
330 void __init page_address_init(void)
331 {
332         int i;
333
334         INIT_LIST_HEAD(&page_address_pool);
335         for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
336                 list_add(&page_address_maps[i].list, &page_address_pool);
337         for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
338                 INIT_LIST_HEAD(&page_address_htable[i].lh);
339                 spin_lock_init(&page_address_htable[i].lock);
340         }
341         spin_lock_init(&pool_lock);
342 }
343
344 #endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */