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