highmem: Export totalhigh_pages.
[linux-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 EXPORT_SYMBOL(totalhigh_pages);
44
45 unsigned int nr_free_highpages (void)
46 {
47         pg_data_t *pgdat;
48         unsigned int pages = 0;
49
50         for_each_online_pgdat(pgdat) {
51                 pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
52                         NR_FREE_PAGES);
53                 if (zone_movable_is_highmem())
54                         pages += zone_page_state(
55                                         &pgdat->node_zones[ZONE_MOVABLE],
56                                         NR_FREE_PAGES);
57         }
58
59         return pages;
60 }
61
62 static int pkmap_count[LAST_PKMAP];
63 static unsigned int last_pkmap_nr;
64 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
65
66 pte_t * pkmap_page_table;
67
68 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
69
70 static void flush_all_zero_pkmaps(void)
71 {
72         int i;
73
74         flush_cache_kmaps();
75
76         for (i = 0; i < LAST_PKMAP; i++) {
77                 struct page *page;
78
79                 /*
80                  * zero means we don't have anything to do,
81                  * >1 means that it is still in use. Only
82                  * a count of 1 means that it is free but
83                  * needs to be unmapped
84                  */
85                 if (pkmap_count[i] != 1)
86                         continue;
87                 pkmap_count[i] = 0;
88
89                 /* sanity check */
90                 BUG_ON(pte_none(pkmap_page_table[i]));
91
92                 /*
93                  * Don't need an atomic fetch-and-clear op here;
94                  * no-one has the page mapped, and cannot get at
95                  * its virtual address (and hence PTE) without first
96                  * getting the kmap_lock (which is held here).
97                  * So no dangers, even with speculative execution.
98                  */
99                 page = pte_page(pkmap_page_table[i]);
100                 pte_clear(&init_mm, (unsigned long)page_address(page),
101                           &pkmap_page_table[i]);
102
103                 set_page_address(page, NULL);
104         }
105         flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
106 }
107
108 /**
109  * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
110  */
111 void kmap_flush_unused(void)
112 {
113         spin_lock(&kmap_lock);
114         flush_all_zero_pkmaps();
115         spin_unlock(&kmap_lock);
116 }
117
118 static inline unsigned long map_new_virtual(struct page *page)
119 {
120         unsigned long vaddr;
121         int count;
122
123 start:
124         count = LAST_PKMAP;
125         /* Find an empty entry */
126         for (;;) {
127                 last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
128                 if (!last_pkmap_nr) {
129                         flush_all_zero_pkmaps();
130                         count = LAST_PKMAP;
131                 }
132                 if (!pkmap_count[last_pkmap_nr])
133                         break;  /* Found a usable entry */
134                 if (--count)
135                         continue;
136
137                 /*
138                  * Sleep for somebody else to unmap their entries
139                  */
140                 {
141                         DECLARE_WAITQUEUE(wait, current);
142
143                         __set_current_state(TASK_UNINTERRUPTIBLE);
144                         add_wait_queue(&pkmap_map_wait, &wait);
145                         spin_unlock(&kmap_lock);
146                         schedule();
147                         remove_wait_queue(&pkmap_map_wait, &wait);
148                         spin_lock(&kmap_lock);
149
150                         /* Somebody else might have mapped it while we slept */
151                         if (page_address(page))
152                                 return (unsigned long)page_address(page);
153
154                         /* Re-start */
155                         goto start;
156                 }
157         }
158         vaddr = PKMAP_ADDR(last_pkmap_nr);
159         set_pte_at(&init_mm, vaddr,
160                    &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
161
162         pkmap_count[last_pkmap_nr] = 1;
163         set_page_address(page, (void *)vaddr);
164
165         return vaddr;
166 }
167
168 /**
169  * kmap_high - map a highmem page into memory
170  * @page: &struct page to map
171  *
172  * Returns the page's virtual memory address.
173  *
174  * We cannot call this from interrupts, as it may block.
175  */
176 void *kmap_high(struct page *page)
177 {
178         unsigned long vaddr;
179
180         /*
181          * For highmem pages, we can't trust "virtual" until
182          * after we have the lock.
183          */
184         spin_lock(&kmap_lock);
185         vaddr = (unsigned long)page_address(page);
186         if (!vaddr)
187                 vaddr = map_new_virtual(page);
188         pkmap_count[PKMAP_NR(vaddr)]++;
189         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
190         spin_unlock(&kmap_lock);
191         return (void*) vaddr;
192 }
193
194 EXPORT_SYMBOL(kmap_high);
195
196 /**
197  * kunmap_high - map a highmem page into memory
198  * @page: &struct page to unmap
199  */
200 void kunmap_high(struct page *page)
201 {
202         unsigned long vaddr;
203         unsigned long nr;
204         int need_wakeup;
205
206         spin_lock(&kmap_lock);
207         vaddr = (unsigned long)page_address(page);
208         BUG_ON(!vaddr);
209         nr = PKMAP_NR(vaddr);
210
211         /*
212          * A count must never go down to zero
213          * without a TLB flush!
214          */
215         need_wakeup = 0;
216         switch (--pkmap_count[nr]) {
217         case 0:
218                 BUG();
219         case 1:
220                 /*
221                  * Avoid an unnecessary wake_up() function call.
222                  * The common case is pkmap_count[] == 1, but
223                  * no waiters.
224                  * The tasks queued in the wait-queue are guarded
225                  * by both the lock in the wait-queue-head and by
226                  * the kmap_lock.  As the kmap_lock is held here,
227                  * no need for the wait-queue-head's lock.  Simply
228                  * test if the queue is empty.
229                  */
230                 need_wakeup = waitqueue_active(&pkmap_map_wait);
231         }
232         spin_unlock(&kmap_lock);
233
234         /* do wake-up, if needed, race-free outside of the spin lock */
235         if (need_wakeup)
236                 wake_up(&pkmap_map_wait);
237 }
238
239 EXPORT_SYMBOL(kunmap_high);
240 #endif
241
242 #if defined(HASHED_PAGE_VIRTUAL)
243
244 #define PA_HASH_ORDER   7
245
246 /*
247  * Describes one page->virtual association
248  */
249 struct page_address_map {
250         struct page *page;
251         void *virtual;
252         struct list_head list;
253 };
254
255 /*
256  * page_address_map freelist, allocated from page_address_maps.
257  */
258 static struct list_head page_address_pool;      /* freelist */
259 static spinlock_t pool_lock;                    /* protects page_address_pool */
260
261 /*
262  * Hash table bucket
263  */
264 static struct page_address_slot {
265         struct list_head lh;                    /* List of page_address_maps */
266         spinlock_t lock;                        /* Protect this bucket's list */
267 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
268
269 static struct page_address_slot *page_slot(struct page *page)
270 {
271         return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
272 }
273
274 /**
275  * page_address - get the mapped virtual address of a page
276  * @page: &struct page to get the virtual address of
277  *
278  * Returns the page's virtual address.
279  */
280 void *page_address(struct page *page)
281 {
282         unsigned long flags;
283         void *ret;
284         struct page_address_slot *pas;
285
286         if (!PageHighMem(page))
287                 return lowmem_page_address(page);
288
289         pas = page_slot(page);
290         ret = NULL;
291         spin_lock_irqsave(&pas->lock, flags);
292         if (!list_empty(&pas->lh)) {
293                 struct page_address_map *pam;
294
295                 list_for_each_entry(pam, &pas->lh, list) {
296                         if (pam->page == page) {
297                                 ret = pam->virtual;
298                                 goto done;
299                         }
300                 }
301         }
302 done:
303         spin_unlock_irqrestore(&pas->lock, flags);
304         return ret;
305 }
306
307 EXPORT_SYMBOL(page_address);
308
309 /**
310  * set_page_address - set a page's virtual address
311  * @page: &struct page to set
312  * @virtual: virtual address to use
313  */
314 void set_page_address(struct page *page, void *virtual)
315 {
316         unsigned long flags;
317         struct page_address_slot *pas;
318         struct page_address_map *pam;
319
320         BUG_ON(!PageHighMem(page));
321
322         pas = page_slot(page);
323         if (virtual) {          /* Add */
324                 BUG_ON(list_empty(&page_address_pool));
325
326                 spin_lock_irqsave(&pool_lock, flags);
327                 pam = list_entry(page_address_pool.next,
328                                 struct page_address_map, list);
329                 list_del(&pam->list);
330                 spin_unlock_irqrestore(&pool_lock, flags);
331
332                 pam->page = page;
333                 pam->virtual = virtual;
334
335                 spin_lock_irqsave(&pas->lock, flags);
336                 list_add_tail(&pam->list, &pas->lh);
337                 spin_unlock_irqrestore(&pas->lock, flags);
338         } else {                /* Remove */
339                 spin_lock_irqsave(&pas->lock, flags);
340                 list_for_each_entry(pam, &pas->lh, list) {
341                         if (pam->page == page) {
342                                 list_del(&pam->list);
343                                 spin_unlock_irqrestore(&pas->lock, flags);
344                                 spin_lock_irqsave(&pool_lock, flags);
345                                 list_add_tail(&pam->list, &page_address_pool);
346                                 spin_unlock_irqrestore(&pool_lock, flags);
347                                 goto done;
348                         }
349                 }
350                 spin_unlock_irqrestore(&pas->lock, flags);
351         }
352 done:
353         return;
354 }
355
356 static struct page_address_map page_address_maps[LAST_PKMAP];
357
358 void __init page_address_init(void)
359 {
360         int i;
361
362         INIT_LIST_HEAD(&page_address_pool);
363         for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
364                 list_add(&page_address_maps[i].list, &page_address_pool);
365         for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
366                 INIT_LIST_HEAD(&page_address_htable[i].lh);
367                 spin_lock_init(&page_address_htable[i].lock);
368         }
369         spin_lock_init(&pool_lock);
370 }
371
372 #endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */