mm: introduce for_each_populated_zone() macro

[mirror_ubuntu-zesty-kernel.git] / mm / vmstat.c

/*
 *  linux/mm/vmstat.c
 *
 *  Manages VM statistics
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  zoned VM statistics
 *  Copyright (C) 2006 Silicon Graphics, Inc.,
 *              Christoph Lameter <christoph@lameter.com>
 */
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/vmstat.h>
#include <linux/sched.h>

#ifdef CONFIG_VM_EVENT_COUNTERS
DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
EXPORT_PER_CPU_SYMBOL(vm_event_states);

static void sum_vm_events(unsigned long *ret, const struct cpumask *cpumask)
{
        int cpu;
        int i;

        memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));

        for_each_cpu(cpu, cpumask) {
                struct vm_event_state *this = &per_cpu(vm_event_states, cpu);

                for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
                        ret[i] += this->event[i];
        }
}

/*
 * Accumulate the vm event counters across all CPUs.
 * The result is unavoidably approximate - it can change
 * during and after execution of this function.
*/
void all_vm_events(unsigned long *ret)
{
        get_online_cpus();
        sum_vm_events(ret, cpu_online_mask);
        put_online_cpus();
}
EXPORT_SYMBOL_GPL(all_vm_events);

#ifdef CONFIG_HOTPLUG
/*
 * Fold the foreign cpu events into our own.
 *
 * This is adding to the events on one processor
 * but keeps the global counts constant.
 */
void vm_events_fold_cpu(int cpu)
{
        struct vm_event_state *fold_state = &per_cpu(vm_event_states, cpu);
        int i;

        for (i = 0; i < NR_VM_EVENT_ITEMS; i++) {
                count_vm_events(i, fold_state->event[i]);
                fold_state->event[i] = 0;
        }
}
#endif /* CONFIG_HOTPLUG */

#endif /* CONFIG_VM_EVENT_COUNTERS */

/*
 * Manage combined zone based / global counters
 *
 * vm_stat contains the global counters
 */
atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
EXPORT_SYMBOL(vm_stat);

#ifdef CONFIG_SMP

static int calculate_threshold(struct zone *zone)
{
        int threshold;
        int mem;        /* memory in 128 MB units */

        /*
         * The threshold scales with the number of processors and the amount
         * of memory per zone. More memory means that we can defer updates for
         * longer, more processors could lead to more contention.
         * fls() is used to have a cheap way of logarithmic scaling.
         *
         * Some sample thresholds:
         *
         * Threshold    Processors      (fls)   Zonesize        fls(mem+1)
         * ------------------------------------------------------------------
         * 8            1               1       0.9-1 GB        4
         * 16           2               2       0.9-1 GB        4
         * 20           2               2       1-2 GB          5
         * 24           2               2       2-4 GB          6
         * 28           2               2       4-8 GB          7
         * 32           2               2       8-16 GB         8
         * 4            2               2       <128M           1
         * 30           4               3       2-4 GB          5
         * 48           4               3       8-16 GB         8
         * 32           8               4       1-2 GB          4
         * 32           8               4       0.9-1GB         4
         * 10           16              5       <128M           1
         * 40           16              5       900M            4
         * 70           64              7       2-4 GB          5
         * 84           64              7       4-8 GB          6
         * 108          512             9       4-8 GB          6
         * 125          1024            10      8-16 GB         8
         * 125          1024            10      16-32 GB        9
         */

        mem = zone->present_pages >> (27 - PAGE_SHIFT);

        threshold = 2 * fls(num_online_cpus()) * (1 + fls(mem));

        /*
         * Maximum threshold is 125
         */
        threshold = min(125, threshold);

        return threshold;
}

/*
 * Refresh the thresholds for each zone.
 */
static void refresh_zone_stat_thresholds(void)
{
        struct zone *zone;
        int cpu;
        int threshold;

        for_each_populated_zone(zone) {
                threshold = calculate_threshold(zone);

                for_each_online_cpu(cpu)
                        zone_pcp(zone, cpu)->stat_threshold = threshold;
        }
}

/*
 * For use when we know that interrupts are disabled.
 */
void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
                                int delta)
{
        struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
        s8 *p = pcp->vm_stat_diff + item;
        long x;

        x = delta + *p;

        if (unlikely(x > pcp->stat_threshold || x < -pcp->stat_threshold)) {
                zone_page_state_add(x, zone, item);
                x = 0;
        }
        *p = x;
}
EXPORT_SYMBOL(__mod_zone_page_state);

/*
 * For an unknown interrupt state
 */
void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
                                        int delta)
{
        unsigned long flags;

        local_irq_save(flags);
        __mod_zone_page_state(zone, item, delta);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(mod_zone_page_state);

/*
 * Optimized increment and decrement functions.
 *
 * These are only for a single page and therefore can take a struct page *
 * argument instead of struct zone *. This allows the inclusion of the code
 * generated for page_zone(page) into the optimized functions.
 *
 * No overflow check is necessary and therefore the differential can be
 * incremented or decremented in place which may allow the compilers to
 * generate better code.
 * The increment or decrement is known and therefore one boundary check can
 * be omitted.
 *
 * NOTE: These functions are very performance sensitive. Change only
 * with care.
 *
 * Some processors have inc/dec instructions that are atomic vs an interrupt.
 * However, the code must first determine the differential location in a zone
 * based on the processor number and then inc/dec the counter. There is no
 * guarantee without disabling preemption that the processor will not change
 * in between and therefore the atomicity vs. interrupt cannot be exploited
 * in a useful way here.
 */
void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
{
        struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
        s8 *p = pcp->vm_stat_diff + item;

        (*p)++;

        if (unlikely(*p > pcp->stat_threshold)) {
                int overstep = pcp->stat_threshold / 2;

                zone_page_state_add(*p + overstep, zone, item);
                *p = -overstep;
        }
}

void __inc_zone_page_state(struct page *page, enum zone_stat_item item)
{
        __inc_zone_state(page_zone(page), item);
}
EXPORT_SYMBOL(__inc_zone_page_state);

void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
{
        struct per_cpu_pageset *pcp = zone_pcp(zone, smp_processor_id());
        s8 *p = pcp->vm_stat_diff + item;

        (*p)--;

        if (unlikely(*p < - pcp->stat_threshold)) {
                int overstep = pcp->stat_threshold / 2;

                zone_page_state_add(*p - overstep, zone, item);
                *p = overstep;
        }
}

void __dec_zone_page_state(struct page *page, enum zone_stat_item item)
{
        __dec_zone_state(page_zone(page), item);
}
EXPORT_SYMBOL(__dec_zone_page_state);

void inc_zone_state(struct zone *zone, enum zone_stat_item item)
{
        unsigned long flags;

        local_irq_save(flags);
        __inc_zone_state(zone, item);
        local_irq_restore(flags);
}

void inc_zone_page_state(struct page *page, enum zone_stat_item item)
{
        unsigned long flags;
        struct zone *zone;

        zone = page_zone(page);
        local_irq_save(flags);
        __inc_zone_state(zone, item);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(inc_zone_page_state);

void dec_zone_page_state(struct page *page, enum zone_stat_item item)
{
        unsigned long flags;

        local_irq_save(flags);
        __dec_zone_page_state(page, item);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(dec_zone_page_state);

/*
 * Update the zone counters for one cpu.
 *
 * The cpu specified must be either the current cpu or a processor that
 * is not online. If it is the current cpu then the execution thread must
 * be pinned to the current cpu.
 *
 * Note that refresh_cpu_vm_stats strives to only access
 * node local memory. The per cpu pagesets on remote zones are placed
 * in the memory local to the processor using that pageset. So the
 * loop over all zones will access a series of cachelines local to
 * the processor.
 *
 * The call to zone_page_state_add updates the cachelines with the
 * statistics in the remote zone struct as well as the global cachelines
 * with the global counters. These could cause remote node cache line
 * bouncing and will have to be only done when necessary.
 */
void refresh_cpu_vm_stats(int cpu)
{
        struct zone *zone;
        int i;
        int global_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };

        for_each_populated_zone(zone) {
                struct per_cpu_pageset *p;

                p = zone_pcp(zone, cpu);

                for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
                        if (p->vm_stat_diff[i]) {
                                unsigned long flags;
                                int v;

                                local_irq_save(flags);
                                v = p->vm_stat_diff[i];
                                p->vm_stat_diff[i] = 0;
                                local_irq_restore(flags);
                                atomic_long_add(v, &zone->vm_stat[i]);
                                global_diff[i] += v;
#ifdef CONFIG_NUMA
                                /* 3 seconds idle till flush */
                                p->expire = 3;
#endif
                        }
                cond_resched();
#ifdef CONFIG_NUMA
                /*
                 * Deal with draining the remote pageset of this
                 * processor
                 *
                 * Check if there are pages remaining in this pageset
                 * if not then there is nothing to expire.
                 */
                if (!p->expire || !p->pcp.count)
                        continue;

                /*
                 * We never drain zones local to this processor.
                 */
                if (zone_to_nid(zone) == numa_node_id()) {
                        p->expire = 0;
                        continue;
                }

                p->expire--;
                if (p->expire)
                        continue;

                if (p->pcp.count)
                        drain_zone_pages(zone, &p->pcp);
#endif
        }

        for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
                if (global_diff[i])
                        atomic_long_add(global_diff[i], &vm_stat[i]);
}

#endif

#ifdef CONFIG_NUMA
/*
 * zonelist = the list of zones passed to the allocator
 * z        = the zone from which the allocation occurred.
 *
 * Must be called with interrupts disabled.
 */
void zone_statistics(struct zone *preferred_zone, struct zone *z)
{
        if (z->zone_pgdat == preferred_zone->zone_pgdat) {
                __inc_zone_state(z, NUMA_HIT);
        } else {
                __inc_zone_state(z, NUMA_MISS);
                __inc_zone_state(preferred_zone, NUMA_FOREIGN);
        }
        if (z->node == numa_node_id())
                __inc_zone_state(z, NUMA_LOCAL);
        else
                __inc_zone_state(z, NUMA_OTHER);
}
#endif

#ifdef CONFIG_PROC_FS
#include <linux/proc_fs.h>
#include <linux/seq_file.h>

static char * const migratetype_names[MIGRATE_TYPES] = {
        "Unmovable",
        "Reclaimable",
        "Movable",
        "Reserve",
        "Isolate",
};

static void *frag_start(struct seq_file *m, loff_t *pos)
{
        pg_data_t *pgdat;
        loff_t node = *pos;
        for (pgdat = first_online_pgdat();
             pgdat && node;
             pgdat = next_online_pgdat(pgdat))
                --node;

        return pgdat;
}

static void *frag_next(struct seq_file *m, void *arg, loff_t *pos)
{
        pg_data_t *pgdat = (pg_data_t *)arg;

        (*pos)++;
        return next_online_pgdat(pgdat);
}

static void frag_stop(struct seq_file *m, void *arg)
{
}

/* Walk all the zones in a node and print using a callback */
static void walk_zones_in_node(struct seq_file *m, pg_data_t *pgdat,
                void (*print)(struct seq_file *m, pg_data_t *, struct zone *))
{
        struct zone *zone;
        struct zone *node_zones = pgdat->node_zones;
        unsigned long flags;

        for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
                if (!populated_zone(zone))
                        continue;

                spin_lock_irqsave(&zone->lock, flags);
                print(m, pgdat, zone);
                spin_unlock_irqrestore(&zone->lock, flags);
        }
}

static void frag_show_print(struct seq_file *m, pg_data_t *pgdat,
                                                struct zone *zone)
{
        int order;

        seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
        for (order = 0; order < MAX_ORDER; ++order)
                seq_printf(m, "%6lu ", zone->free_area[order].nr_free);
        seq_putc(m, '\n');
}

/*
 * This walks the free areas for each zone.
 */
static int frag_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = (pg_data_t *)arg;
        walk_zones_in_node(m, pgdat, frag_show_print);
        return 0;
}

static void pagetypeinfo_showfree_print(struct seq_file *m,
                                        pg_data_t *pgdat, struct zone *zone)
{
        int order, mtype;

        for (mtype = 0; mtype < MIGRATE_TYPES; mtype++) {
                seq_printf(m, "Node %4d, zone %8s, type %12s ",
                                        pgdat->node_id,
                                        zone->name,
                                        migratetype_names[mtype]);
                for (order = 0; order < MAX_ORDER; ++order) {
                        unsigned long freecount = 0;
                        struct free_area *area;
                        struct list_head *curr;

                        area = &(zone->free_area[order]);

                        list_for_each(curr, &area->free_list[mtype])
                                freecount++;
                        seq_printf(m, "%6lu ", freecount);
                }
                seq_putc(m, '\n');
        }
}

/* Print out the free pages at each order for each migatetype */
static int pagetypeinfo_showfree(struct seq_file *m, void *arg)
{
        int order;
        pg_data_t *pgdat = (pg_data_t *)arg;

        /* Print header */
        seq_printf(m, "%-43s ", "Free pages count per migrate type at order");
        for (order = 0; order < MAX_ORDER; ++order)
                seq_printf(m, "%6d ", order);
        seq_putc(m, '\n');

        walk_zones_in_node(m, pgdat, pagetypeinfo_showfree_print);

        return 0;
}

static void pagetypeinfo_showblockcount_print(struct seq_file *m,
                                        pg_data_t *pgdat, struct zone *zone)
{
        int mtype;
        unsigned long pfn;
        unsigned long start_pfn = zone->zone_start_pfn;
        unsigned long end_pfn = start_pfn + zone->spanned_pages;
        unsigned long count[MIGRATE_TYPES] = { 0, };

        for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
                struct page *page;

                if (!pfn_valid(pfn))
                        continue;

                page = pfn_to_page(pfn);
#ifdef CONFIG_ARCH_FLATMEM_HAS_HOLES
                /*
                 * Ordinarily, memory holes in flatmem still have a valid
                 * memmap for the PFN range. However, an architecture for
                 * embedded systems (e.g. ARM) can free up the memmap backing
                 * holes to save memory on the assumption the memmap is
                 * never used. The page_zone linkages are then broken even
                 * though pfn_valid() returns true. Skip the page if the
                 * linkages are broken. Even if this test passed, the impact
                 * is that the counters for the movable type are off but
                 * fragmentation monitoring is likely meaningless on small
                 * systems.
                 */
                if (page_zone(page) != zone)
                        continue;
#endif
                mtype = get_pageblock_migratetype(page);

                if (mtype < MIGRATE_TYPES)
                        count[mtype]++;
        }

        /* Print counts */
        seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
        for (mtype = 0; mtype < MIGRATE_TYPES; mtype++)
                seq_printf(m, "%12lu ", count[mtype]);
        seq_putc(m, '\n');
}

/* Print out the free pages at each order for each migratetype */
static int pagetypeinfo_showblockcount(struct seq_file *m, void *arg)
{
        int mtype;
        pg_data_t *pgdat = (pg_data_t *)arg;

        seq_printf(m, "\n%-23s", "Number of blocks type ");
        for (mtype = 0; mtype < MIGRATE_TYPES; mtype++)
                seq_printf(m, "%12s ", migratetype_names[mtype]);
        seq_putc(m, '\n');
        walk_zones_in_node(m, pgdat, pagetypeinfo_showblockcount_print);

        return 0;
}

/*
 * This prints out statistics in relation to grouping pages by mobility.
 * It is expensive to collect so do not constantly read the file.
 */
static int pagetypeinfo_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = (pg_data_t *)arg;

        /* check memoryless node */
        if (!node_state(pgdat->node_id, N_HIGH_MEMORY))
                return 0;

        seq_printf(m, "Page block order: %d\n", pageblock_order);
        seq_printf(m, "Pages per block:  %lu\n", pageblock_nr_pages);
        seq_putc(m, '\n');
        pagetypeinfo_showfree(m, pgdat);
        pagetypeinfo_showblockcount(m, pgdat);

        return 0;
}

static const struct seq_operations fragmentation_op = {
        .start  = frag_start,
        .next   = frag_next,
        .stop   = frag_stop,
        .show   = frag_show,
};

static int fragmentation_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &fragmentation_op);
}

static const struct file_operations fragmentation_file_operations = {
        .open           = fragmentation_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

static const struct seq_operations pagetypeinfo_op = {
        .start  = frag_start,
        .next   = frag_next,
        .stop   = frag_stop,
        .show   = pagetypeinfo_show,
};

static int pagetypeinfo_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &pagetypeinfo_op);
}

static const struct file_operations pagetypeinfo_file_ops = {
        .open           = pagetypeinfo_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

#ifdef CONFIG_ZONE_DMA
#define TEXT_FOR_DMA(xx) xx "_dma",
#else
#define TEXT_FOR_DMA(xx)
#endif

#ifdef CONFIG_ZONE_DMA32
#define TEXT_FOR_DMA32(xx) xx "_dma32",
#else
#define TEXT_FOR_DMA32(xx)
#endif

#ifdef CONFIG_HIGHMEM
#define TEXT_FOR_HIGHMEM(xx) xx "_high",
#else
#define TEXT_FOR_HIGHMEM(xx)
#endif

#define TEXTS_FOR_ZONES(xx) TEXT_FOR_DMA(xx) TEXT_FOR_DMA32(xx) xx "_normal", \
                                        TEXT_FOR_HIGHMEM(xx) xx "_movable",

static const char * const vmstat_text[] = {
        /* Zoned VM counters */
        "nr_free_pages",
        "nr_inactive_anon",
        "nr_active_anon",
        "nr_inactive_file",
        "nr_active_file",
#ifdef CONFIG_UNEVICTABLE_LRU
        "nr_unevictable",
        "nr_mlock",
#endif
        "nr_anon_pages",
        "nr_mapped",
        "nr_file_pages",
        "nr_dirty",
        "nr_writeback",
        "nr_slab_reclaimable",
        "nr_slab_unreclaimable",
        "nr_page_table_pages",
        "nr_unstable",
        "nr_bounce",
        "nr_vmscan_write",
        "nr_writeback_temp",

#ifdef CONFIG_NUMA
        "numa_hit",
        "numa_miss",
        "numa_foreign",
        "numa_interleave",
        "numa_local",
        "numa_other",
#endif

#ifdef CONFIG_VM_EVENT_COUNTERS
        "pgpgin",
        "pgpgout",
        "pswpin",
        "pswpout",

        TEXTS_FOR_ZONES("pgalloc")

        "pgfree",
        "pgactivate",
        "pgdeactivate",

        "pgfault",
        "pgmajfault",

        TEXTS_FOR_ZONES("pgrefill")
        TEXTS_FOR_ZONES("pgsteal")
        TEXTS_FOR_ZONES("pgscan_kswapd")
        TEXTS_FOR_ZONES("pgscan_direct")

        "pginodesteal",
        "slabs_scanned",
        "kswapd_steal",
        "kswapd_inodesteal",
        "pageoutrun",
        "allocstall",

        "pgrotated",
#ifdef CONFIG_HUGETLB_PAGE
        "htlb_buddy_alloc_success",
        "htlb_buddy_alloc_fail",
#endif
#ifdef CONFIG_UNEVICTABLE_LRU
        "unevictable_pgs_culled",
        "unevictable_pgs_scanned",
        "unevictable_pgs_rescued",
        "unevictable_pgs_mlocked",
        "unevictable_pgs_munlocked",
        "unevictable_pgs_cleared",
        "unevictable_pgs_stranded",
        "unevictable_pgs_mlockfreed",
#endif
#endif
};

static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
                                                        struct zone *zone)
{
        int i;
        seq_printf(m, "Node %d, zone %8s", pgdat->node_id, zone->name);
        seq_printf(m,
                   "\n  pages free     %lu"
                   "\n        min      %lu"
                   "\n        low      %lu"
                   "\n        high     %lu"
                   "\n        scanned  %lu (aa: %lu ia: %lu af: %lu if: %lu)"
                   "\n        spanned  %lu"
                   "\n        present  %lu",
                   zone_page_state(zone, NR_FREE_PAGES),
                   zone->pages_min,
                   zone->pages_low,
                   zone->pages_high,
                   zone->pages_scanned,
                   zone->lru[LRU_ACTIVE_ANON].nr_scan,
                   zone->lru[LRU_INACTIVE_ANON].nr_scan,
                   zone->lru[LRU_ACTIVE_FILE].nr_scan,
                   zone->lru[LRU_INACTIVE_FILE].nr_scan,
                   zone->spanned_pages,
                   zone->present_pages);

        for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
                seq_printf(m, "\n    %-12s %lu", vmstat_text[i],
                                zone_page_state(zone, i));

        seq_printf(m,
                   "\n        protection: (%lu",
                   zone->lowmem_reserve[0]);
        for (i = 1; i < ARRAY_SIZE(zone->lowmem_reserve); i++)
                seq_printf(m, ", %lu", zone->lowmem_reserve[i]);
        seq_printf(m,
                   ")"
                   "\n  pagesets");
        for_each_online_cpu(i) {
                struct per_cpu_pageset *pageset;

                pageset = zone_pcp(zone, i);
                seq_printf(m,
                           "\n    cpu: %i"
                           "\n              count: %i"
                           "\n              high:  %i"
                           "\n              batch: %i",
                           i,
                           pageset->pcp.count,
                           pageset->pcp.high,
                           pageset->pcp.batch);
#ifdef CONFIG_SMP
                seq_printf(m, "\n  vm stats threshold: %d",
                                pageset->stat_threshold);
#endif
        }
        seq_printf(m,
                   "\n  all_unreclaimable: %u"
                   "\n  prev_priority:     %i"
                   "\n  start_pfn:         %lu"
                   "\n  inactive_ratio:    %u",
                           zone_is_all_unreclaimable(zone),
                   zone->prev_priority,
                   zone->zone_start_pfn,
                   zone->inactive_ratio);
        seq_putc(m, '\n');
}

/*
 * Output information about zones in @pgdat.
 */
static int zoneinfo_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = (pg_data_t *)arg;
        walk_zones_in_node(m, pgdat, zoneinfo_show_print);
        return 0;
}

static const struct seq_operations zoneinfo_op = {
        .start  = frag_start, /* iterate over all zones. The same as in
                               * fragmentation. */
        .next   = frag_next,
        .stop   = frag_stop,
        .show   = zoneinfo_show,
};

static int zoneinfo_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &zoneinfo_op);
}

static const struct file_operations proc_zoneinfo_file_operations = {
        .open           = zoneinfo_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

static void *vmstat_start(struct seq_file *m, loff_t *pos)
{
        unsigned long *v;
#ifdef CONFIG_VM_EVENT_COUNTERS
        unsigned long *e;
#endif
        int i;

        if (*pos >= ARRAY_SIZE(vmstat_text))
                return NULL;

#ifdef CONFIG_VM_EVENT_COUNTERS
        v = kmalloc(NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long)
                        + sizeof(struct vm_event_state), GFP_KERNEL);
#else
        v = kmalloc(NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long),
                        GFP_KERNEL);
#endif
        m->private = v;
        if (!v)
                return ERR_PTR(-ENOMEM);
        for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
                v[i] = global_page_state(i);
#ifdef CONFIG_VM_EVENT_COUNTERS
        e = v + NR_VM_ZONE_STAT_ITEMS;
        all_vm_events(e);
        e[PGPGIN] /= 2;         /* sectors -> kbytes */
        e[PGPGOUT] /= 2;
#endif
        return v + *pos;
}

static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos)
{
        (*pos)++;
        if (*pos >= ARRAY_SIZE(vmstat_text))
                return NULL;
        return (unsigned long *)m->private + *pos;
}

static int vmstat_show(struct seq_file *m, void *arg)
{
        unsigned long *l = arg;
        unsigned long off = l - (unsigned long *)m->private;

        seq_printf(m, "%s %lu\n", vmstat_text[off], *l);
        return 0;
}

static void vmstat_stop(struct seq_file *m, void *arg)
{
        kfree(m->private);
        m->private = NULL;
}

static const struct seq_operations vmstat_op = {
        .start  = vmstat_start,
        .next   = vmstat_next,
        .stop   = vmstat_stop,
        .show   = vmstat_show,
};

static int vmstat_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &vmstat_op);
}

static const struct file_operations proc_vmstat_file_operations = {
        .open           = vmstat_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};
#endif /* CONFIG_PROC_FS */

#ifdef CONFIG_SMP
static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
int sysctl_stat_interval __read_mostly = HZ;

static void vmstat_update(struct work_struct *w)
{
        refresh_cpu_vm_stats(smp_processor_id());
        schedule_delayed_work(&__get_cpu_var(vmstat_work),
                sysctl_stat_interval);
}

static void __cpuinit start_cpu_timer(int cpu)
{
        struct delayed_work *vmstat_work = &per_cpu(vmstat_work, cpu);

        INIT_DELAYED_WORK_DEFERRABLE(vmstat_work, vmstat_update);
        schedule_delayed_work_on(cpu, vmstat_work, HZ + cpu);
}

/*
 * Use the cpu notifier to insure that the thresholds are recalculated
 * when necessary.
 */
static int __cpuinit vmstat_cpuup_callback(struct notifier_block *nfb,
                unsigned long action,
                void *hcpu)
{
        long cpu = (long)hcpu;

        switch (action) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                start_cpu_timer(cpu);
                break;
        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
                cancel_rearming_delayed_work(&per_cpu(vmstat_work, cpu));
                per_cpu(vmstat_work, cpu).work.func = NULL;
                break;
        case CPU_DOWN_FAILED:
        case CPU_DOWN_FAILED_FROZEN:
                start_cpu_timer(cpu);
                break;
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                refresh_zone_stat_thresholds();
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata vmstat_notifier =
        { &vmstat_cpuup_callback, NULL, 0 };
#endif

static int __init setup_vmstat(void)
{
#ifdef CONFIG_SMP
        int cpu;

        refresh_zone_stat_thresholds();
        register_cpu_notifier(&vmstat_notifier);

        for_each_online_cpu(cpu)
                start_cpu_timer(cpu);
#endif
#ifdef CONFIG_PROC_FS
        proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);
        proc_create("pagetypeinfo", S_IRUGO, NULL, &pagetypeinfo_file_ops);
        proc_create("vmstat", S_IRUGO, NULL, &proc_vmstat_file_operations);
        proc_create("zoneinfo", S_IRUGO, NULL, &proc_zoneinfo_file_operations);
#endif
        return 0;
}
module_init(setup_vmstat)