mm/swap.c

   1 /*
   2  *  linux/mm/swap.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5  */
   6
   7 /*
   8  * This file contains the default values for the opereation of the
   9  * Linux VM subsystem. Fine-tuning documentation can be found in
  10  * Documentation/sysctl/vm.txt.
  11  * Started 18.12.91
  12  * Swap aging added 23.2.95, Stephen Tweedie.
  13  * Buffermem limits added 12.3.98, Rik van Riel.
  14  */
  15
  16 #include <linux/mm.h>
  17 #include <linux/sched.h>
  18 #include <linux/kernel_stat.h>
  19 #include <linux/swap.h>
  20 #include <linux/mman.h>
  21 #include <linux/pagemap.h>
  22 #include <linux/pagevec.h>
  23 #include <linux/init.h>
  24 #include <linux/module.h>
  25 #include <linux/mm_inline.h>
  26 #include <linux/buffer_head.h>  /* for try_to_release_page() */
  27 #include <linux/module.h>
  28 #include <linux/percpu_counter.h>
  29 #include <linux/percpu.h>
  30 #include <linux/cpu.h>
  31 #include <linux/notifier.h>
  32 #include <linux/init.h>
  33
  34 /* How many pages do we try to swap or page in/out together? */
  35 int page_cluster;
  36
  37 void put_page(struct page *page)
  38 {
  39         if (unlikely(PageCompound(page))) {
  40                 page = (struct page *)page_private(page);
  41                 if (put_page_testzero(page)) {
  42                         void (*dtor)(struct page *page);
  43
  44                         dtor = (void (*)(struct page *))page[1].mapping;
  45                         (*dtor)(page);
  46                 }
  47                 return;
  48         }
  49         if (put_page_testzero(page))
  50                 __page_cache_release(page);
  51 }
  52 EXPORT_SYMBOL(put_page);
  53
  54 /*
  55  * Writeback is about to end against a page which has been marked for immediate
  56  * reclaim.  If it still appears to be reclaimable, move it to the tail of the
  57  * inactive list.  The page still has PageWriteback set, which will pin it.
  58  *
  59  * We don't expect many pages to come through here, so don't bother batching
  60  * things up.
  61  *
  62  * To avoid placing the page at the tail of the LRU while PG_writeback is still
  63  * set, this function will clear PG_writeback before performing the page
  64  * motion.  Do that inside the lru lock because once PG_writeback is cleared
  65  * we may not touch the page.
  66  *
  67  * Returns zero if it cleared PG_writeback.
  68  */
  69 int rotate_reclaimable_page(struct page *page)
  70 {
  71         struct zone *zone;
  72         unsigned long flags;
  73
  74         if (PageLocked(page))
  75                 return 1;
  76         if (PageDirty(page))
  77                 return 1;
  78         if (PageActive(page))
  79                 return 1;
  80         if (!PageLRU(page))
  81                 return 1;
  82
  83         zone = page_zone(page);
  84         spin_lock_irqsave(&zone->lru_lock, flags);
  85         if (PageLRU(page) && !PageActive(page)) {
  86                 list_del(&page->lru);
  87                 list_add_tail(&page->lru, &zone->inactive_list);
  88                 inc_page_state(pgrotated);
  89         }
  90         if (!test_clear_page_writeback(page))
  91                 BUG();
  92         spin_unlock_irqrestore(&zone->lru_lock, flags);
  93         return 0;
  94 }
  95
  96 /*
  97  * FIXME: speed this up?
  98  */
  99 void fastcall activate_page(struct page *page)
 100 {
 101         struct zone *zone = page_zone(page);
 102
 103         spin_lock_irq(&zone->lru_lock);
 104         if (PageLRU(page) && !PageActive(page)) {
 105                 del_page_from_inactive_list(zone, page);
 106                 SetPageActive(page);
 107                 add_page_to_active_list(zone, page);
 108                 inc_page_state(pgactivate);
 109         }
 110         spin_unlock_irq(&zone->lru_lock);
 111 }
 112
 113 /*
 114  * Mark a page as having seen activity.
 115  *
 116  * inactive,unreferenced        ->      inactive,referenced
 117  * inactive,referenced          ->      active,unreferenced
 118  * active,unreferenced          ->      active,referenced
 119  */
 120 void fastcall mark_page_accessed(struct page *page)
 121 {
 122         if (!PageActive(page) && PageReferenced(page) && PageLRU(page)) {
 123                 activate_page(page);
 124                 ClearPageReferenced(page);
 125         } else if (!PageReferenced(page)) {
 126                 SetPageReferenced(page);
 127         }
 128 }
 129
 130 EXPORT_SYMBOL(mark_page_accessed);
 131
 132 /**
 133  * lru_cache_add: add a page to the page lists
 134  * @page: the page to add
 135  */
 136 static DEFINE_PER_CPU(struct pagevec, lru_add_pvecs) = { 0, };
 137 static DEFINE_PER_CPU(struct pagevec, lru_add_active_pvecs) = { 0, };
 138
 139 void fastcall lru_cache_add(struct page *page)
 140 {
 141         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs);
 142
 143         page_cache_get(page);
 144         if (!pagevec_add(pvec, page))
 145                 __pagevec_lru_add(pvec);
 146         put_cpu_var(lru_add_pvecs);
 147 }
 148
 149 void fastcall lru_cache_add_active(struct page *page)
 150 {
 151         struct pagevec *pvec = &get_cpu_var(lru_add_active_pvecs);
 152
 153         page_cache_get(page);
 154         if (!pagevec_add(pvec, page))
 155                 __pagevec_lru_add_active(pvec);
 156         put_cpu_var(lru_add_active_pvecs);
 157 }
 158
 159 static void __lru_add_drain(int cpu)
 160 {
 161         struct pagevec *pvec = &per_cpu(lru_add_pvecs, cpu);
 162
 163         /* CPU is dead, so no locking needed. */
 164         if (pagevec_count(pvec))
 165                 __pagevec_lru_add(pvec);
 166         pvec = &per_cpu(lru_add_active_pvecs, cpu);
 167         if (pagevec_count(pvec))
 168                 __pagevec_lru_add_active(pvec);
 169 }
 170
 171 void lru_add_drain(void)
 172 {
 173         __lru_add_drain(get_cpu());
 174         put_cpu();
 175 }
 176
 177 /*
 178  * This path almost never happens for VM activity - pages are normally
 179  * freed via pagevecs.  But it gets used by networking.
 180  */
 181 void fastcall __page_cache_release(struct page *page)
 182 {
 183         unsigned long flags;
 184         struct zone *zone = page_zone(page);
 185
 186         spin_lock_irqsave(&zone->lru_lock, flags);
 187         if (TestClearPageLRU(page))
 188                 del_page_from_lru(zone, page);
 189         if (page_count(page) != 0)
 190                 page = NULL;
 191         spin_unlock_irqrestore(&zone->lru_lock, flags);
 192         if (page)
 193                 free_hot_page(page);
 194 }
 195
 196 EXPORT_SYMBOL(__page_cache_release);
 197
 198 /*
 199  * Batched page_cache_release().  Decrement the reference count on all the
 200  * passed pages.  If it fell to zero then remove the page from the LRU and
 201  * free it.
 202  *
 203  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
 204  * for the remainder of the operation.
 205  *
 206  * The locking in this function is against shrink_cache(): we recheck the
 207  * page count inside the lock to see whether shrink_cache grabbed the page
 208  * via the LRU.  If it did, give up: shrink_cache will free it.
 209  */
 210 void release_pages(struct page **pages, int nr, int cold)
 211 {
 212         int i;
 213         struct pagevec pages_to_free;
 214         struct zone *zone = NULL;
 215
 216         pagevec_init(&pages_to_free, cold);
 217         for (i = 0; i < nr; i++) {
 218                 struct page *page = pages[i];
 219                 struct zone *pagezone;
 220
 221                 if (!put_page_testzero(page))
 222                         continue;
 223
 224                 pagezone = page_zone(page);
 225                 if (pagezone != zone) {
 226                         if (zone)
 227                                 spin_unlock_irq(&zone->lru_lock);
 228                         zone = pagezone;
 229                         spin_lock_irq(&zone->lru_lock);
 230                 }
 231                 if (TestClearPageLRU(page))
 232                         del_page_from_lru(zone, page);
 233                 if (page_count(page) == 0) {
 234                         if (!pagevec_add(&pages_to_free, page)) {
 235                                 spin_unlock_irq(&zone->lru_lock);
 236                                 __pagevec_free(&pages_to_free);
 237                                 pagevec_reinit(&pages_to_free);
 238                                 zone = NULL;    /* No lock is held */
 239                         }
 240                 }
 241         }
 242         if (zone)
 243                 spin_unlock_irq(&zone->lru_lock);
 244
 245         pagevec_free(&pages_to_free);
 246 }
 247
 248 /*
 249  * The pages which we're about to release may be in the deferred lru-addition
 250  * queues.  That would prevent them from really being freed right now.  That's
 251  * OK from a correctness point of view but is inefficient - those pages may be
 252  * cache-warm and we want to give them back to the page allocator ASAP.
 253  *
 254  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
 255  * and __pagevec_lru_add_active() call release_pages() directly to avoid
 256  * mutual recursion.
 257  */
 258 void __pagevec_release(struct pagevec *pvec)
 259 {
 260         lru_add_drain();
 261         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
 262         pagevec_reinit(pvec);
 263 }
 264
 265 EXPORT_SYMBOL(__pagevec_release);
 266
 267 /*
 268  * pagevec_release() for pages which are known to not be on the LRU
 269  *
 270  * This function reinitialises the caller's pagevec.
 271  */
 272 void __pagevec_release_nonlru(struct pagevec *pvec)
 273 {
 274         int i;
 275         struct pagevec pages_to_free;
 276
 277         pagevec_init(&pages_to_free, pvec->cold);
 278         for (i = 0; i < pagevec_count(pvec); i++) {
 279                 struct page *page = pvec->pages[i];
 280
 281                 BUG_ON(PageLRU(page));
 282                 if (put_page_testzero(page))
 283                         pagevec_add(&pages_to_free, page);
 284         }
 285         pagevec_free(&pages_to_free);
 286         pagevec_reinit(pvec);
 287 }
 288
 289 /*
 290  * Add the passed pages to the LRU, then drop the caller's refcount
 291  * on them.  Reinitialises the caller's pagevec.
 292  */
 293 void __pagevec_lru_add(struct pagevec *pvec)
 294 {
 295         int i;
 296         struct zone *zone = NULL;
 297
 298         for (i = 0; i < pagevec_count(pvec); i++) {
 299                 struct page *page = pvec->pages[i];
 300                 struct zone *pagezone = page_zone(page);
 301
 302                 if (pagezone != zone) {
 303                         if (zone)
 304                                 spin_unlock_irq(&zone->lru_lock);
 305                         zone = pagezone;
 306                         spin_lock_irq(&zone->lru_lock);
 307                 }
 308                 if (TestSetPageLRU(page))
 309                         BUG();
 310                 add_page_to_inactive_list(zone, page);
 311         }
 312         if (zone)
 313                 spin_unlock_irq(&zone->lru_lock);
 314         release_pages(pvec->pages, pvec->nr, pvec->cold);
 315         pagevec_reinit(pvec);
 316 }
 317
 318 EXPORT_SYMBOL(__pagevec_lru_add);
 319
 320 void __pagevec_lru_add_active(struct pagevec *pvec)
 321 {
 322         int i;
 323         struct zone *zone = NULL;
 324
 325         for (i = 0; i < pagevec_count(pvec); i++) {
 326                 struct page *page = pvec->pages[i];
 327                 struct zone *pagezone = page_zone(page);
 328
 329                 if (pagezone != zone) {
 330                         if (zone)
 331                                 spin_unlock_irq(&zone->lru_lock);
 332                         zone = pagezone;
 333                         spin_lock_irq(&zone->lru_lock);
 334                 }
 335                 if (TestSetPageLRU(page))
 336                         BUG();
 337                 if (TestSetPageActive(page))
 338                         BUG();
 339                 add_page_to_active_list(zone, page);
 340         }
 341         if (zone)
 342                 spin_unlock_irq(&zone->lru_lock);
 343         release_pages(pvec->pages, pvec->nr, pvec->cold);
 344         pagevec_reinit(pvec);
 345 }
 346
 347 /*
 348  * Try to drop buffers from the pages in a pagevec
 349  */
 350 void pagevec_strip(struct pagevec *pvec)
 351 {
 352         int i;
 353
 354         for (i = 0; i < pagevec_count(pvec); i++) {
 355                 struct page *page = pvec->pages[i];
 356
 357                 if (PagePrivate(page) && !TestSetPageLocked(page)) {
 358                         try_to_release_page(page, 0);
 359                         unlock_page(page);
 360                 }
 361         }
 362 }
 363
 364 /**
 365  * pagevec_lookup - gang pagecache lookup
 366  * @pvec:       Where the resulting pages are placed
 367  * @mapping:    The address_space to search
 368  * @start:      The starting page index
 369  * @nr_pages:   The maximum number of pages
 370  *
 371  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
 372  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
 373  * reference against the pages in @pvec.
 374  *
 375  * The search returns a group of mapping-contiguous pages with ascending
 376  * indexes.  There may be holes in the indices due to not-present pages.
 377  *
 378  * pagevec_lookup() returns the number of pages which were found.
 379  */
 380 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 381                 pgoff_t start, unsigned nr_pages)
 382 {
 383         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
 384         return pagevec_count(pvec);
 385 }
 386
 387 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
 388                 pgoff_t *index, int tag, unsigned nr_pages)
 389 {
 390         pvec->nr = find_get_pages_tag(mapping, index, tag,
 391                                         nr_pages, pvec->pages);
 392         return pagevec_count(pvec);
 393 }
 394
 395 EXPORT_SYMBOL(pagevec_lookup_tag);
 396
 397 #ifdef CONFIG_SMP
 398 /*
 399  * We tolerate a little inaccuracy to avoid ping-ponging the counter between
 400  * CPUs
 401  */
 402 #define ACCT_THRESHOLD  max(16, NR_CPUS * 2)
 403
 404 static DEFINE_PER_CPU(long, committed_space) = 0;
 405
 406 void vm_acct_memory(long pages)
 407 {
 408         long *local;
 409
 410         preempt_disable();
 411         local = &__get_cpu_var(committed_space);
 412         *local += pages;
 413         if (*local > ACCT_THRESHOLD || *local < -ACCT_THRESHOLD) {
 414                 atomic_add(*local, &vm_committed_space);
 415                 *local = 0;
 416         }
 417         preempt_enable();
 418 }
 419
 420 #ifdef CONFIG_HOTPLUG_CPU
 421
 422 /* Drop the CPU's cached committed space back into the central pool. */
 423 static int cpu_swap_callback(struct notifier_block *nfb,
 424                              unsigned long action,
 425                              void *hcpu)
 426 {
 427         long *committed;
 428
 429         committed = &per_cpu(committed_space, (long)hcpu);
 430         if (action == CPU_DEAD) {
 431                 atomic_add(*committed, &vm_committed_space);
 432                 *committed = 0;
 433                 __lru_add_drain((long)hcpu);
 434         }
 435         return NOTIFY_OK;
 436 }
 437 #endif /* CONFIG_HOTPLUG_CPU */
 438 #endif /* CONFIG_SMP */
 439
 440 #ifdef CONFIG_SMP
 441 void percpu_counter_mod(struct percpu_counter *fbc, long amount)
 442 {
 443         long count;
 444         long *pcount;
 445         int cpu = get_cpu();
 446
 447         pcount = per_cpu_ptr(fbc->counters, cpu);
 448         count = *pcount + amount;
 449         if (count >= FBC_BATCH || count <= -FBC_BATCH) {
 450                 spin_lock(&fbc->lock);
 451                 fbc->count += count;
 452                 spin_unlock(&fbc->lock);
 453                 count = 0;
 454         }
 455         *pcount = count;
 456         put_cpu();
 457 }
 458 EXPORT_SYMBOL(percpu_counter_mod);
 459 #endif
 460
 461 /*
 462  * Perform any setup for the swap system
 463  */
 464 void __init swap_setup(void)
 465 {
 466         unsigned long megs = num_physpages >> (20 - PAGE_SHIFT);
 467
 468         /* Use a smaller cluster for small-memory machines */
 469         if (megs < 16)
 470                 page_cluster = 2;
 471         else
 472                 page_cluster = 3;
 473         /*
 474          * Right now other parts of the system means that we
 475          * _really_ don't want to cluster much more
 476          */
 477         hotcpu_notifier(cpu_swap_callback, 0);
 478 }