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) */