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         int need_flush = 0;
  74
  75         flush_cache_kmaps();
  76
  77         for (i = 0; i < LAST_PKMAP; i++) {
  78                 struct page *page;
  79
  80                 /*
  81                  * zero means we don't have anything to do,
  82                  * >1 means that it is still in use. Only
  83                  * a count of 1 means that it is free but
  84                  * needs to be unmapped
  85                  */
  86                 if (pkmap_count[i] != 1)
  87                         continue;
  88                 pkmap_count[i] = 0;
  89
  90                 /* sanity check */
  91                 BUG_ON(pte_none(pkmap_page_table[i]));
  92
  93                 /*
  94                  * Don't need an atomic fetch-and-clear op here;
  95                  * no-one has the page mapped, and cannot get at
  96                  * its virtual address (and hence PTE) without first
  97                  * getting the kmap_lock (which is held here).
  98                  * So no dangers, even with speculative execution.
  99                  */
 100                 page = pte_page(pkmap_page_table[i]);
 101                 pte_clear(&init_mm, (unsigned long)page_address(page),
 102                           &pkmap_page_table[i]);
 103
 104                 set_page_address(page, NULL);
 105                 need_flush = 1;
 106         }
 107         if (need_flush)
 108                 flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 109 }
 110
 111 /**
 112  * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
 113  */
 114 void kmap_flush_unused(void)
 115 {
 116         spin_lock(&kmap_lock);
 117         flush_all_zero_pkmaps();
 118         spin_unlock(&kmap_lock);
 119 }
 120
 121 static inline unsigned long map_new_virtual(struct page *page)
 122 {
 123         unsigned long vaddr;
 124         int count;
 125
 126 start:
 127         count = LAST_PKMAP;
 128         /* Find an empty entry */
 129         for (;;) {
 130                 last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
 131                 if (!last_pkmap_nr) {
 132                         flush_all_zero_pkmaps();
 133                         count = LAST_PKMAP;
 134                 }
 135                 if (!pkmap_count[last_pkmap_nr])
 136                         break;  /* Found a usable entry */
 137                 if (--count)
 138                         continue;
 139
 140                 /*
 141                  * Sleep for somebody else to unmap their entries
 142                  */
 143                 {
 144                         DECLARE_WAITQUEUE(wait, current);
 145
 146                         __set_current_state(TASK_UNINTERRUPTIBLE);
 147                         add_wait_queue(&pkmap_map_wait, &wait);
 148                         spin_unlock(&kmap_lock);
 149                         schedule();
 150                         remove_wait_queue(&pkmap_map_wait, &wait);
 151                         spin_lock(&kmap_lock);
 152
 153                         /* Somebody else might have mapped it while we slept */
 154                         if (page_address(page))
 155                                 return (unsigned long)page_address(page);
 156
 157                         /* Re-start */
 158                         goto start;
 159                 }
 160         }
 161         vaddr = PKMAP_ADDR(last_pkmap_nr);
 162         set_pte_at(&init_mm, vaddr,
 163                    &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
 164
 165         pkmap_count[last_pkmap_nr] = 1;
 166         set_page_address(page, (void *)vaddr);
 167
 168         return vaddr;
 169 }
 170
 171 /**
 172  * kmap_high - map a highmem page into memory
 173  * @page: &struct page to map
 174  *
 175  * Returns the page's virtual memory address.
 176  *
 177  * We cannot call this from interrupts, as it may block.
 178  */
 179 void *kmap_high(struct page *page)
 180 {
 181         unsigned long vaddr;
 182
 183         /*
 184          * For highmem pages, we can't trust "virtual" until
 185          * after we have the lock.
 186          */
 187         spin_lock(&kmap_lock);
 188         vaddr = (unsigned long)page_address(page);
 189         if (!vaddr)
 190                 vaddr = map_new_virtual(page);
 191         pkmap_count[PKMAP_NR(vaddr)]++;
 192         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
 193         spin_unlock(&kmap_lock);
 194         return (void*) vaddr;
 195 }
 196
 197 EXPORT_SYMBOL(kmap_high);
 198
 199 /**
 200  * kunmap_high - map a highmem page into memory
 201  * @page: &struct page to unmap
 202  */
 203 void kunmap_high(struct page *page)
 204 {
 205         unsigned long vaddr;
 206         unsigned long nr;
 207         int need_wakeup;
 208
 209         spin_lock(&kmap_lock);
 210         vaddr = (unsigned long)page_address(page);
 211         BUG_ON(!vaddr);
 212         nr = PKMAP_NR(vaddr);
 213
 214         /*
 215          * A count must never go down to zero
 216          * without a TLB flush!
 217          */
 218         need_wakeup = 0;
 219         switch (--pkmap_count[nr]) {
 220         case 0:
 221                 BUG();
 222         case 1:
 223                 /*
 224                  * Avoid an unnecessary wake_up() function call.
 225                  * The common case is pkmap_count[] == 1, but
 226                  * no waiters.
 227                  * The tasks queued in the wait-queue are guarded
 228                  * by both the lock in the wait-queue-head and by
 229                  * the kmap_lock.  As the kmap_lock is held here,
 230                  * no need for the wait-queue-head's lock.  Simply
 231                  * test if the queue is empty.
 232                  */
 233                 need_wakeup = waitqueue_active(&pkmap_map_wait);
 234         }
 235         spin_unlock(&kmap_lock);
 236
 237         /* do wake-up, if needed, race-free outside of the spin lock */
 238         if (need_wakeup)
 239                 wake_up(&pkmap_map_wait);
 240 }
 241
 242 EXPORT_SYMBOL(kunmap_high);
 243 #endif
 244
 245 #if defined(HASHED_PAGE_VIRTUAL)
 246
 247 #define PA_HASH_ORDER   7
 248
 249 /*
 250  * Describes one page->virtual association
 251  */
 252 struct page_address_map {
 253         struct page *page;
 254         void *virtual;
 255         struct list_head list;
 256 };
 257
 258 /*
 259  * page_address_map freelist, allocated from page_address_maps.
 260  */
 261 static struct list_head page_address_pool;      /* freelist */
 262 static spinlock_t pool_lock;                    /* protects page_address_pool */
 263
 264 /*
 265  * Hash table bucket
 266  */
 267 static struct page_address_slot {
 268         struct list_head lh;                    /* List of page_address_maps */
 269         spinlock_t lock;                        /* Protect this bucket's list */
 270 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
 271
 272 static struct page_address_slot *page_slot(struct page *page)
 273 {
 274         return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 275 }
 276
 277 /**
 278  * page_address - get the mapped virtual address of a page
 279  * @page: &struct page to get the virtual address of
 280  *
 281  * Returns the page's virtual address.
 282  */
 283 void *page_address(struct page *page)
 284 {
 285         unsigned long flags;
 286         void *ret;
 287         struct page_address_slot *pas;
 288
 289         if (!PageHighMem(page))
 290                 return lowmem_page_address(page);
 291
 292         pas = page_slot(page);
 293         ret = NULL;
 294         spin_lock_irqsave(&pas->lock, flags);
 295         if (!list_empty(&pas->lh)) {
 296                 struct page_address_map *pam;
 297
 298                 list_for_each_entry(pam, &pas->lh, list) {
 299                         if (pam->page == page) {
 300                                 ret = pam->virtual;
 301                                 goto done;
 302                         }
 303                 }
 304         }
 305 done:
 306         spin_unlock_irqrestore(&pas->lock, flags);
 307         return ret;
 308 }
 309
 310 EXPORT_SYMBOL(page_address);
 311
 312 /**
 313  * set_page_address - set a page's virtual address
 314  * @page: &struct page to set
 315  * @virtual: virtual address to use
 316  */
 317 void set_page_address(struct page *page, void *virtual)
 318 {
 319         unsigned long flags;
 320         struct page_address_slot *pas;
 321         struct page_address_map *pam;
 322
 323         BUG_ON(!PageHighMem(page));
 324
 325         pas = page_slot(page);
 326         if (virtual) {          /* Add */
 327                 BUG_ON(list_empty(&page_address_pool));
 328
 329                 spin_lock_irqsave(&pool_lock, flags);
 330                 pam = list_entry(page_address_pool.next,
 331                                 struct page_address_map, list);
 332                 list_del(&pam->list);
 333                 spin_unlock_irqrestore(&pool_lock, flags);
 334
 335                 pam->page = page;
 336                 pam->virtual = virtual;
 337
 338                 spin_lock_irqsave(&pas->lock, flags);
 339                 list_add_tail(&pam->list, &pas->lh);
 340                 spin_unlock_irqrestore(&pas->lock, flags);
 341         } else {                /* Remove */
 342                 spin_lock_irqsave(&pas->lock, flags);
 343                 list_for_each_entry(pam, &pas->lh, list) {
 344                         if (pam->page == page) {
 345                                 list_del(&pam->list);
 346                                 spin_unlock_irqrestore(&pas->lock, flags);
 347                                 spin_lock_irqsave(&pool_lock, flags);
 348                                 list_add_tail(&pam->list, &page_address_pool);
 349                                 spin_unlock_irqrestore(&pool_lock, flags);
 350                                 goto done;
 351                         }
 352                 }
 353                 spin_unlock_irqrestore(&pas->lock, flags);
 354         }
 355 done:
 356         return;
 357 }
 358
 359 static struct page_address_map page_address_maps[LAST_PKMAP];
 360
 361 void __init page_address_init(void)
 362 {
 363         int i;
 364
 365         INIT_LIST_HEAD(&page_address_pool);
 366         for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
 367                 list_add(&page_address_maps[i].list, &page_address_pool);
 368         for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
 369                 INIT_LIST_HEAD(&page_address_htable[i].lh);
 370                 spin_lock_init(&page_address_htable[i].lock);
 371         }
 372         spin_lock_init(&pool_lock);
 373 }
 374
 375 #endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */