mm/vmstat.c

   1 /*
   2  *  linux/mm/vmstat.c
   3  *
   4  *  Manages VM statistics
   5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   6  *
   7  *  zoned VM statistics
   8  *  Copyright (C) 2006 Silicon Graphics, Inc.,
   9  *              Christoph Lameter <christoph@lameter.com>
  10  */
  11
  12 #include <linux/mm.h>
  13 #include <linux/module.h>
  14 #include <linux/cpu.h>
  15
  16 #ifdef CONFIG_VM_EVENT_COUNTERS
  17 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
  18 EXPORT_PER_CPU_SYMBOL(vm_event_states);
  19
  20 static void sum_vm_events(unsigned long *ret, cpumask_t *cpumask)
  21 {
  22         int cpu = 0;
  23         int i;
  24
  25         memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));
  26
  27         cpu = first_cpu(*cpumask);
  28         while (cpu < NR_CPUS) {
  29                 struct vm_event_state *this = &per_cpu(vm_event_states, cpu);
  30
  31                 cpu = next_cpu(cpu, *cpumask);
  32
  33                 if (cpu < NR_CPUS)
  34                         prefetch(&per_cpu(vm_event_states, cpu));
  35
  36
  37                 for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
  38                         ret[i] += this->event[i];
  39         }
  40 }
  41
  42 /*
  43  * Accumulate the vm event counters across all CPUs.
  44  * The result is unavoidably approximate - it can change
  45  * during and after execution of this function.
  46 */
  47 void all_vm_events(unsigned long *ret)
  48 {
  49         sum_vm_events(ret, &cpu_online_map);
  50 }
  51 EXPORT_SYMBOL_GPL(all_vm_events);
  52
  53 #ifdef CONFIG_HOTPLUG
  54 /*
  55  * Fold the foreign cpu events into our own.
  56  *
  57  * This is adding to the events on one processor
  58  * but keeps the global counts constant.
  59  */
  60 void vm_events_fold_cpu(int cpu)
  61 {
  62         struct vm_event_state *fold_state = &per_cpu(vm_event_states, cpu);
  63         int i;
  64
  65         for (i = 0; i < NR_VM_EVENT_ITEMS; i++) {
  66                 count_vm_events(i, fold_state->event[i]);
  67                 fold_state->event[i] = 0;
  68         }
  69 }
  70 #endif /* CONFIG_HOTPLUG */
  71
  72 #endif /* CONFIG_VM_EVENT_COUNTERS */
  73
  74 /*
  75  * Manage combined zone based / global counters
  76  *
  77  * vm_stat contains the global counters
  78  */
  79 atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
  80 EXPORT_SYMBOL(vm_stat);
  81
  82 #ifdef CONFIG_SMP
  83
  84 static int calculate_threshold(struct zone *zone)
  85 {
  86         int threshold;
  87         int mem;        /* memory in 128 MB units */
  88
  89         /*
  90          * The threshold scales with the number of processors and the amount
  91          * of memory per zone. More memory means that we can defer updates for
  92          * longer, more processors could lead to more contention.
  93          * fls() is used to have a cheap way of logarithmic scaling.
  94          *
  95          * Some sample thresholds:
  96          *
  97          * Threshold    Processors      (fls)   Zonesize        fls(mem+1)
  98          * ------------------------------------------------------------------
  99          * 8            1               1       0.9-1 GB        4
 100          * 16           2               2       0.9-1 GB        4
 101          * 20           2               2       1-2 GB          5
 102          * 24           2               2       2-4 GB          6
 103          * 28           2               2       4-8 GB          7
 104          * 32           2               2       8-16 GB         8
 105          * 4            2               2       <128M           1
 106          * 30           4               3       2-4 GB          5
 107          * 48           4               3       8-16 GB         8
 108          * 32           8               4       1-2 GB          4
 109          * 32           8               4       0.9-1GB         4
 110          * 10           16              5       <128M           1
 111          * 40           16              5       900M            4
 112          * 70           64              7       2-4 GB          5
 113          * 84           64              7       4-8 GB          6
 114          * 108          512             9       4-8 GB          6
 115          * 125          1024            10      8-16 GB         8
 116          * 125          1024            10      16-32 GB        9
 117          */
 118
 119         mem = zone->present_pages >> (27 - PAGE_SHIFT);
 120
 121         threshold = 2 * fls(num_online_cpus()) * (1 + fls(mem));
 122
 123         /*
 124          * Maximum threshold is 125
 125          */
 126         threshold = min(125, threshold);
 127
 128         return threshold;
 129 }
 130
 131 /*
 132  * Refresh the thresholds for each zone.
 133  */
 134 static void refresh_zone_stat_thresholds(void)
 135 {
 136         struct zone *zone;
 137         int cpu;
 138         int threshold;
 139
 140         for_each_zone(zone) {
 141
 142                 if (!zone->present_pages)
 143                         continue;
 144
 145                 threshold = calculate_threshold(zone);
 146
 147                 for_each_online_cpu(cpu)
 148                         zone_pcp(zone, cpu)->stat_threshold = threshold;
 149         }
 150 }
 151
 152 /*
 153  * For use when we know that interrupts are disabled.
 154  */
 155 void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 156                                 int delta)
 157 {
 158         struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
 159         s8 *p = pcp->vm_stat_diff + item;
 160         long x;
 161
 162         x = delta + *p;
 163
 164         if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
 165                 zone_page_state_add(x, zone, item);
 166                 x = 0;
 167         }
 168         *p = x;
 169 }
 170 EXPORT_SYMBOL(__mod_zone_page_state);
 171
 172 /*
 173  * For an unknown interrupt state
 174  */
 175 void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
 176                                         int delta)
 177 {
 178         unsigned long flags;
 179
 180         local_irq_save(flags);
 181         __mod_zone_page_state(zone, item, delta);
 182         local_irq_restore(flags);
 183 }
 184 EXPORT_SYMBOL(mod_zone_page_state);
 185
 186 /*
 187  * Optimized increment and decrement functions.
 188  *
 189  * These are only for a single page and therefore can take a struct page *
 190  * argument instead of struct zone *. This allows the inclusion of the code
 191  * generated for page_zone(page) into the optimized functions.
 192  *
 193  * No overflow check is necessary and therefore the differential can be
 194  * incremented or decremented in place which may allow the compilers to
 195  * generate better code.
 196  * The increment or decrement is known and therefore one boundary check can
 197  * be omitted.
 198  *
 199  * NOTE: These functions are very performance sensitive. Change only
 200  * with care.
 201  *
 202  * Some processors have inc/dec instructions that are atomic vs an interrupt.
 203  * However, the code must first determine the differential location in a zone
 204  * based on the processor number and then inc/dec the counter. There is no
 205  * guarantee without disabling preemption that the processor will not change
 206  * in between and therefore the atomicity vs. interrupt cannot be exploited
 207  * in a useful way here.
 208  */
 209 void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
 210 {
 211         struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
 212         s8 *p = pcp->vm_stat_diff + item;
 213
 214         (*p)++;
 215
 216         if (unlikely(*p > pcp->stat_threshold)) {
 217                 int overstep = pcp->stat_threshold / 2;
 218
 219                 zone_page_state_add(*p + overstep, zone, item);
 220                 *p = -overstep;
 221         }
 222 }
 223
 224 void __inc_zone_page_state(struct page *page, enum zone_stat_item item)
 225 {
 226         __inc_zone_state(page_zone(page), item);
 227 }
 228 EXPORT_SYMBOL(__inc_zone_page_state);
 229
 230 void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
 231 {
 232         struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
 233         s8 *p = pcp->vm_stat_diff + item;
 234
 235         (*p)--;
 236
 237         if (unlikely(*p < - pcp->stat_threshold)) {
 238                 int overstep = pcp->stat_threshold / 2;
 239
 240                 zone_page_state_add(*p - overstep, zone, item);
 241                 *p = overstep;
 242         }
 243 }
 244
 245 void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
 246 {
 247         __dec_zone_state(page_zone(page), item);
 248 }
 249 EXPORT_SYMBOL(__dec_zone_page_state);
 250
 251 void inc_zone_state(struct zone *zone, enum zone_stat_item item)
 252 {
 253         unsigned long flags;
 254
 255         local_irq_save(flags);
 256         __inc_zone_state(zone, item);
 257         local_irq_restore(flags);
 258 }
 259
 260 void inc_zone_page_state(struct page *page, enum zone_stat_item item)
 261 {
 262         unsigned long flags;
 263         struct zone *zone;
 264
 265         zone = page_zone(page);
 266         local_irq_save(flags);
 267         __inc_zone_state(zone, item);
 268         local_irq_restore(flags);
 269 }
 270 EXPORT_SYMBOL(inc_zone_page_state);
 271
 272 void dec_zone_page_state(struct page *page, enum zone_stat_item item)
 273 {
 274         unsigned long flags;
 275
 276         local_irq_save(flags);
 277         __dec_zone_page_state(page, item);
 278         local_irq_restore(flags);
 279 }
 280 EXPORT_SYMBOL(dec_zone_page_state);
 281
 282 /*
 283  * Update the zone counters for one cpu.
 284  *
 285  * Note that refresh_cpu_vm_stats strives to only access
 286  * node local memory. The per cpu pagesets on remote zones are placed
 287  * in the memory local to the processor using that pageset. So the
 288  * loop over all zones will access a series of cachelines local to
 289  * the processor.
 290  *
 291  * The call to zone_page_state_add updates the cachelines with the
 292  * statistics in the remote zone struct as well as the global cachelines
 293  * with the global counters. These could cause remote node cache line
 294  * bouncing and will have to be only done when necessary.
 295  */
 296 void refresh_cpu_vm_stats(int cpu)
 297 {
 298         struct zone *zone;
 299         int i;
 300         unsigned long flags;
 301
 302         for_each_zone(zone) {
 303                 struct per_cpu_pageset *p;
 304
 305                 if (!populated_zone(zone))
 306                         continue;
 307
 308                 p = zone_pcp(zone, cpu);
 309
 310                 for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 311                         if (p->vm_stat_diff[i]) {
 312                                 local_irq_save(flags);
 313                                 zone_page_state_add(p->vm_stat_diff[i],
 314                                         zone, i);
 315                                 p->vm_stat_diff[i] = 0;
 316 #ifdef CONFIG_NUMA
 317                                 /* 3 seconds idle till flush */
 318                                 p->expire = 3;
 319 #endif
 320                                 local_irq_restore(flags);
 321                         }
 322 #ifdef CONFIG_NUMA
 323                 /*
 324                  * Deal with draining the remote pageset of this
 325                  * processor
 326                  *
 327                  * Check if there are pages remaining in this pageset
 328                  * if not then there is nothing to expire.
 329                  */
 330                 if (!p->expire || (!p->pcp[0].count && !p->pcp[1].count))
 331                         continue;
 332
 333                 /*
 334                  * We never drain zones local to this processor.
 335                  */
 336                 if (zone_to_nid(zone) == numa_node_id()) {
 337                         p->expire = 0;
 338                         continue;
 339                 }
 340
 341                 p->expire--;
 342                 if (p->expire)
 343                         continue;
 344
 345                 if (p->pcp[0].count)
 346                         drain_zone_pages(zone, p->pcp + 0);
 347
 348                 if (p->pcp[1].count)
 349                         drain_zone_pages(zone, p->pcp + 1);
 350 #endif
 351         }
 352 }
 353
 354 static void __refresh_cpu_vm_stats(void *dummy)
 355 {
 356         refresh_cpu_vm_stats(smp_processor_id());
 357 }
 358
 359 /*
 360  * Consolidate all counters.
 361  *
 362  * Note that the result is less inaccurate but still inaccurate
 363  * if concurrent processes are allowed to run.
 364  */
 365 void refresh_vm_stats(void)
 366 {
 367         on_each_cpu(__refresh_cpu_vm_stats, NULL, 0, 1);
 368 }
 369 EXPORT_SYMBOL(refresh_vm_stats);
 370
 371 #endif
 372
 373 #ifdef CONFIG_NUMA
 374 /*
 375  * zonelist = the list of zones passed to the allocator
 376  * z        = the zone from which the allocation occurred.
 377  *
 378  * Must be called with interrupts disabled.
 379  */
 380 void zone_statistics(struct zonelist *zonelist, struct zone *z)
 381 {
 382         if (z->zone_pgdat == zonelist->zones[0]->zone_pgdat) {
 383                 __inc_zone_state(z, NUMA_HIT);
 384         } else {
 385                 __inc_zone_state(z, NUMA_MISS);
 386                 __inc_zone_state(zonelist->zones[0], NUMA_FOREIGN);
 387         }
 388         if (z->node == numa_node_id())
 389                 __inc_zone_state(z, NUMA_LOCAL);
 390         else
 391                 __inc_zone_state(z, NUMA_OTHER);
 392 }
 393 #endif
 394
 395 #ifdef CONFIG_PROC_FS
 396
 397 #include <linux/seq_file.h>
 398
 399 static void *frag_start(struct seq_file *m, loff_t *pos)
 400 {
 401         pg_data_t *pgdat;
 402         loff_t node = *pos;
 403         for (pgdat = first_online_pgdat();
 404              pgdat && node;
 405              pgdat = next_online_pgdat(pgdat))
 406                 --node;
 407
 408         return pgdat;
 409 }
 410
 411 static void *frag_next(struct seq_file *m, void *arg, loff_t *pos)
 412 {
 413         pg_data_t *pgdat = (pg_data_t *)arg;
 414
 415         (*pos)++;
 416         return next_online_pgdat(pgdat);
 417 }
 418
 419 static void frag_stop(struct seq_file *m, void *arg)
 420 {
 421 }
 422
 423 /*
 424  * This walks the free areas for each zone.
 425  */
 426 static int frag_show(struct seq_file *m, void *arg)
 427 {
 428         pg_data_t *pgdat = (pg_data_t *)arg;
 429         struct zone *zone;
 430         struct zone *node_zones = pgdat->node_zones;
 431         unsigned long flags;
 432         int order;
 433
 434         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
 435                 if (!populated_zone(zone))
 436                         continue;
 437
 438                 spin_lock_irqsave(&zone->lock, flags);
 439                 seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
 440                 for (order = 0; order < MAX_ORDER; ++order)
 441                         seq_printf(m, "%6lu ", zone->free_area[order].nr_free);
 442                 spin_unlock_irqrestore(&zone->lock, flags);
 443                 seq_putc(m, '\n');
 444         }
 445         return 0;
 446 }
 447
 448 const struct seq_operations fragmentation_op = {
 449         .start  = frag_start,
 450         .next   = frag_next,
 451         .stop   = frag_stop,
 452         .show   = frag_show,
 453 };
 454
 455 #ifdef CONFIG_ZONE_DMA
 456 #define TEXT_FOR_DMA(xx) xx "_dma",
 457 #else
 458 #define TEXT_FOR_DMA(xx)
 459 #endif
 460
 461 #ifdef CONFIG_ZONE_DMA32
 462 #define TEXT_FOR_DMA32(xx) xx "_dma32",
 463 #else
 464 #define TEXT_FOR_DMA32(xx)
 465 #endif
 466
 467 #ifdef CONFIG_HIGHMEM
 468 #define TEXT_FOR_HIGHMEM(xx) xx "_high",
 469 #else
 470 #define TEXT_FOR_HIGHMEM(xx)
 471 #endif
 472
 473 #define TEXTS_FOR_ZONES(xx) TEXT_FOR_DMA(xx) TEXT_FOR_DMA32(xx) xx "_normal", \
 474                                         TEXT_FOR_HIGHMEM(xx)
 475
 476 static const char * const vmstat_text[] = {
 477         /* Zoned VM counters */
 478         "nr_free_pages",
 479         "nr_active",
 480         "nr_inactive",
 481         "nr_anon_pages",
 482         "nr_mapped",
 483         "nr_file_pages",
 484         "nr_dirty",
 485         "nr_writeback",
 486         "nr_slab_reclaimable",
 487         "nr_slab_unreclaimable",
 488         "nr_page_table_pages",
 489         "nr_unstable",
 490         "nr_bounce",
 491         "nr_vmscan_write",
 492
 493 #ifdef CONFIG_NUMA
 494         "numa_hit",
 495         "numa_miss",
 496         "numa_foreign",
 497         "numa_interleave",
 498         "numa_local",
 499         "numa_other",
 500 #endif
 501
 502 #ifdef CONFIG_VM_EVENT_COUNTERS
 503         "pgpgin",
 504         "pgpgout",
 505         "pswpin",
 506         "pswpout",
 507
 508         TEXTS_FOR_ZONES("pgalloc")
 509
 510         "pgfree",
 511         "pgactivate",
 512         "pgdeactivate",
 513
 514         "pgfault",
 515         "pgmajfault",
 516
 517         TEXTS_FOR_ZONES("pgrefill")
 518         TEXTS_FOR_ZONES("pgsteal")
 519         TEXTS_FOR_ZONES("pgscan_kswapd")
 520         TEXTS_FOR_ZONES("pgscan_direct")
 521
 522         "pginodesteal",
 523         "slabs_scanned",
 524         "kswapd_steal",
 525         "kswapd_inodesteal",
 526         "pageoutrun",
 527         "allocstall",
 528
 529         "pgrotated",
 530 #endif
 531 };
 532
 533 /*
 534  * Output information about zones in @pgdat.
 535  */
 536 static int zoneinfo_show(struct seq_file *m, void *arg)
 537 {
 538         pg_data_t *pgdat = arg;
 539         struct zone *zone;
 540         struct zone *node_zones = pgdat->node_zones;
 541         unsigned long flags;
 542
 543         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; zone++) {
 544                 int i;
 545
 546                 if (!populated_zone(zone))
 547                         continue;
 548
 549                 spin_lock_irqsave(&zone->lock, flags);
 550                 seq_printf(m, "Node %d, zone %8s", pgdat->node_id, zone->name);
 551                 seq_printf(m,
 552                            "\n  pages free     %lu"
 553                            "\n        min      %lu"
 554                            "\n        low      %lu"
 555                            "\n        high     %lu"
 556                            "\n        scanned  %lu (a: %lu i: %lu)"
 557                            "\n        spanned  %lu"
 558                            "\n        present  %lu",
 559                            zone_page_state(zone, NR_FREE_PAGES),
 560                            zone->pages_min,
 561                            zone->pages_low,
 562                            zone->pages_high,
 563                            zone->pages_scanned,
 564                            zone->nr_scan_active, zone->nr_scan_inactive,
 565                            zone->spanned_pages,
 566                            zone->present_pages);
 567
 568                 for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 569                         seq_printf(m, "\n    %-12s %lu", vmstat_text[i],
 570                                         zone_page_state(zone, i));
 571
 572                 seq_printf(m,
 573                            "\n        protection: (%lu",
 574                            zone->lowmem_reserve[0]);
 575                 for (i = 1; i < ARRAY_SIZE(zone->lowmem_reserve); i++)
 576                         seq_printf(m, ", %lu", zone->lowmem_reserve[i]);
 577                 seq_printf(m,
 578                            ")"
 579                            "\n  pagesets");
 580                 for_each_online_cpu(i) {
 581                         struct per_cpu_pageset *pageset;
 582                         int j;
 583
 584                         pageset = zone_pcp(zone, i);
 585                         for (j = 0; j < ARRAY_SIZE(pageset->pcp); j++) {
 586                                 seq_printf(m,
 587                                            "\n    cpu: %i pcp: %i"
 588                                            "\n              count: %i"
 589                                            "\n              high:  %i"
 590                                            "\n              batch: %i",
 591                                            i, j,
 592                                            pageset->pcp[j].count,
 593                                            pageset->pcp[j].high,
 594                                            pageset->pcp[j].batch);
 595                         }
 596 #ifdef CONFIG_SMP
 597                         seq_printf(m, "\n  vm stats threshold: %d",
 598                                         pageset->stat_threshold);
 599 #endif
 600                 }
 601                 seq_printf(m,
 602                            "\n  all_unreclaimable: %u"
 603                            "\n  prev_priority:     %i"
 604                            "\n  start_pfn:         %lu",
 605                            zone->all_unreclaimable,
 606                            zone->prev_priority,
 607                            zone->zone_start_pfn);
 608                 spin_unlock_irqrestore(&zone->lock, flags);
 609                 seq_putc(m, '\n');
 610         }
 611         return 0;
 612 }
 613
 614 const struct seq_operations zoneinfo_op = {
 615         .start  = frag_start, /* iterate over all zones. The same as in
 616                                * fragmentation. */
 617         .next   = frag_next,
 618         .stop   = frag_stop,
 619         .show   = zoneinfo_show,
 620 };
 621
 622 static void *vmstat_start(struct seq_file *m, loff_t *pos)
 623 {
 624         unsigned long *v;
 625 #ifdef CONFIG_VM_EVENT_COUNTERS
 626         unsigned long *e;
 627 #endif
 628         int i;
 629
 630         if (*pos >= ARRAY_SIZE(vmstat_text))
 631                 return NULL;
 632
 633 #ifdef CONFIG_VM_EVENT_COUNTERS
 634         v = kmalloc(NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long)
 635                         + sizeof(struct vm_event_state), GFP_KERNEL);
 636 #else
 637         v = kmalloc(NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long),
 638                         GFP_KERNEL);
 639 #endif
 640         m->private = v;
 641         if (!v)
 642                 return ERR_PTR(-ENOMEM);
 643         for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 644                 v[i] = global_page_state(i);
 645 #ifdef CONFIG_VM_EVENT_COUNTERS
 646         e = v + NR_VM_ZONE_STAT_ITEMS;
 647         all_vm_events(e);
 648         e[PGPGIN] /= 2;         /* sectors -> kbytes */
 649         e[PGPGOUT] /= 2;
 650 #endif
 651         return v + *pos;
 652 }
 653
 654 static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos)
 655 {
 656         (*pos)++;
 657         if (*pos >= ARRAY_SIZE(vmstat_text))
 658                 return NULL;
 659         return (unsigned long *)m->private + *pos;
 660 }
 661
 662 static int vmstat_show(struct seq_file *m, void *arg)
 663 {
 664         unsigned long *l = arg;
 665         unsigned long off = l - (unsigned long *)m->private;
 666
 667         seq_printf(m, "%s %lu\n", vmstat_text[off], *l);
 668         return 0;
 669 }
 670
 671 static void vmstat_stop(struct seq_file *m, void *arg)
 672 {
 673         kfree(m->private);
 674         m->private = NULL;
 675 }
 676
 677 const struct seq_operations vmstat_op = {
 678         .start  = vmstat_start,
 679         .next   = vmstat_next,
 680         .stop   = vmstat_stop,
 681         .show   = vmstat_show,
 682 };
 683
 684 #endif /* CONFIG_PROC_FS */
 685
 686 #ifdef CONFIG_SMP
 687 static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
 688 int sysctl_stat_interval __read_mostly = HZ;
 689
 690 static void vmstat_update(struct work_struct *w)
 691 {
 692         refresh_cpu_vm_stats(smp_processor_id());
 693         schedule_delayed_work(&__get_cpu_var(vmstat_work),
 694                 sysctl_stat_interval);
 695 }
 696
 697 static void __devinit start_cpu_timer(int cpu)
 698 {
 699         struct delayed_work *vmstat_work = &per_cpu(vmstat_work, cpu);
 700
 701         INIT_DELAYED_WORK(vmstat_work, vmstat_update);
 702         schedule_delayed_work_on(cpu, vmstat_work, HZ + cpu);
 703 }
 704
 705 /*
 706  * Use the cpu notifier to insure that the thresholds are recalculated
 707  * when necessary.
 708  */
 709 static int __cpuinit vmstat_cpuup_callback(struct notifier_block *nfb,
 710                 unsigned long action,
 711                 void *hcpu)
 712 {
 713         long cpu = (long)hcpu;
 714
 715         switch (action) {
 716         case CPU_ONLINE:
 717         case CPU_ONLINE_FROZEN:
 718                 start_cpu_timer(cpu);
 719                 break;
 720         case CPU_DOWN_PREPARE:
 721         case CPU_DOWN_PREPARE_FROZEN:
 722                 cancel_rearming_delayed_work(&per_cpu(vmstat_work, cpu));
 723                 per_cpu(vmstat_work, cpu).work.func = NULL;
 724                 break;
 725         case CPU_DOWN_FAILED:
 726         case CPU_DOWN_FAILED_FROZEN:
 727                 start_cpu_timer(cpu);
 728                 break;
 729         case CPU_DEAD:
 730         case CPU_DEAD_FROZEN:
 731                 refresh_zone_stat_thresholds();
 732                 break;
 733         default:
 734                 break;
 735         }
 736         return NOTIFY_OK;
 737 }
 738
 739 static struct notifier_block __cpuinitdata vmstat_notifier =
 740         { &vmstat_cpuup_callback, NULL, 0 };
 741
 742 int __init setup_vmstat(void)
 743 {
 744         int cpu;
 745
 746         refresh_zone_stat_thresholds();
 747         register_cpu_notifier(&vmstat_notifier);
 748
 749         for_each_online_cpu(cpu)
 750                 start_cpu_timer(cpu);
 751         return 0;
 752 }
 753 module_init(setup_vmstat)
 754 #endif