Linux 4.13.16

[linux/fpc-iii.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>
 *  Copyright (C) 2008-2014 Christoph Lameter
 */
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/vmstat.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/sched.h>
#include <linux/math64.h>
#include <linux/writeback.h>
#include <linux/compaction.h>
#include <linux/mm_inline.h>
#include <linux/page_ext.h>
#include <linux/page_owner.h>

#include "internal.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)
{
        int cpu;
        int i;

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

        for_each_online_cpu(cpu) {
                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);
        put_online_cpus();
}
EXPORT_SYMBOL_GPL(all_vm_events);

/*
 * 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_VM_EVENT_COUNTERS */

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

#ifdef CONFIG_SMP

int calculate_pressure_threshold(struct zone *zone)
{
        int threshold;
        int watermark_distance;

        /*
         * As vmstats are not up to date, there is drift between the estimated
         * and real values. For high thresholds and a high number of CPUs, it
         * is possible for the min watermark to be breached while the estimated
         * value looks fine. The pressure threshold is a reduced value such
         * that even the maximum amount of drift will not accidentally breach
         * the min watermark
         */
        watermark_distance = low_wmark_pages(zone) - min_wmark_pages(zone);
        threshold = max(1, (int)(watermark_distance / num_online_cpus()));

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

        return threshold;
}

int calculate_normal_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->managed_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.
 */
void refresh_zone_stat_thresholds(void)
{
        struct pglist_data *pgdat;
        struct zone *zone;
        int cpu;
        int threshold;

        /* Zero current pgdat thresholds */
        for_each_online_pgdat(pgdat) {
                for_each_online_cpu(cpu) {
                        per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold = 0;
                }
        }

        for_each_populated_zone(zone) {
                struct pglist_data *pgdat = zone->zone_pgdat;
                unsigned long max_drift, tolerate_drift;

                threshold = calculate_normal_threshold(zone);

                for_each_online_cpu(cpu) {
                        int pgdat_threshold;

                        per_cpu_ptr(zone->pageset, cpu)->stat_threshold
                                                        = threshold;

                        /* Base nodestat threshold on the largest populated zone. */
                        pgdat_threshold = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold;
                        per_cpu_ptr(pgdat->per_cpu_nodestats, cpu)->stat_threshold
                                = max(threshold, pgdat_threshold);
                }

                /*
                 * Only set percpu_drift_mark if there is a danger that
                 * NR_FREE_PAGES reports the low watermark is ok when in fact
                 * the min watermark could be breached by an allocation
                 */
                tolerate_drift = low_wmark_pages(zone) - min_wmark_pages(zone);
                max_drift = num_online_cpus() * threshold;
                if (max_drift > tolerate_drift)
                        zone->percpu_drift_mark = high_wmark_pages(zone) +
                                        max_drift;
        }
}

void set_pgdat_percpu_threshold(pg_data_t *pgdat,
                                int (*calculate_pressure)(struct zone *))
{
        struct zone *zone;
        int cpu;
        int threshold;
        int i;

        for (i = 0; i < pgdat->nr_zones; i++) {
                zone = &pgdat->node_zones[i];
                if (!zone->percpu_drift_mark)
                        continue;

                threshold = (*calculate_pressure)(zone);
                for_each_online_cpu(cpu)
                        per_cpu_ptr(zone->pageset, cpu)->stat_threshold
                                                        = threshold;
        }
}

/*
 * For use when we know that interrupts are disabled,
 * or when we know that preemption is disabled and that
 * particular counter cannot be updated from interrupt context.
 */
void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
                           long delta)
{
        struct per_cpu_pageset __percpu *pcp = zone->pageset;
        s8 __percpu *p = pcp->vm_stat_diff + item;
        long x;
        long t;

        x = delta + __this_cpu_read(*p);

        t = __this_cpu_read(pcp->stat_threshold);

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

void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
                                long delta)
{
        struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
        s8 __percpu *p = pcp->vm_node_stat_diff + item;
        long x;
        long t;

        x = delta + __this_cpu_read(*p);

        t = __this_cpu_read(pcp->stat_threshold);

        if (unlikely(x > t || x < -t)) {
                node_page_state_add(x, pgdat, item);
                x = 0;
        }
        __this_cpu_write(*p, x);
}
EXPORT_SYMBOL(__mod_node_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 __percpu *pcp = zone->pageset;
        s8 __percpu *p = pcp->vm_stat_diff + item;
        s8 v, t;

        v = __this_cpu_inc_return(*p);
        t = __this_cpu_read(pcp->stat_threshold);
        if (unlikely(v > t)) {
                s8 overstep = t >> 1;

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

void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
{
        struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
        s8 __percpu *p = pcp->vm_node_stat_diff + item;
        s8 v, t;

        v = __this_cpu_inc_return(*p);
        t = __this_cpu_read(pcp->stat_threshold);
        if (unlikely(v > t)) {
                s8 overstep = t >> 1;

                node_page_state_add(v + overstep, pgdat, item);
                __this_cpu_write(*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 __inc_node_page_state(struct page *page, enum node_stat_item item)
{
        __inc_node_state(page_pgdat(page), item);
}
EXPORT_SYMBOL(__inc_node_page_state);

void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
{
        struct per_cpu_pageset __percpu *pcp = zone->pageset;
        s8 __percpu *p = pcp->vm_stat_diff + item;
        s8 v, t;

        v = __this_cpu_dec_return(*p);
        t = __this_cpu_read(pcp->stat_threshold);
        if (unlikely(v < - t)) {
                s8 overstep = t >> 1;

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

void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
{
        struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
        s8 __percpu *p = pcp->vm_node_stat_diff + item;
        s8 v, t;

        v = __this_cpu_dec_return(*p);
        t = __this_cpu_read(pcp->stat_threshold);
        if (unlikely(v < - t)) {
                s8 overstep = t >> 1;

                node_page_state_add(v - overstep, pgdat, item);
                __this_cpu_write(*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 __dec_node_page_state(struct page *page, enum node_stat_item item)
{
        __dec_node_state(page_pgdat(page), item);
}
EXPORT_SYMBOL(__dec_node_page_state);

#ifdef CONFIG_HAVE_CMPXCHG_LOCAL
/*
 * If we have cmpxchg_local support then we do not need to incur the overhead
 * that comes with local_irq_save/restore if we use this_cpu_cmpxchg.
 *
 * mod_state() modifies the zone counter state through atomic per cpu
 * operations.
 *
 * Overstep mode specifies how overstep should handled:
 *     0       No overstepping
 *     1       Overstepping half of threshold
 *     -1      Overstepping minus half of threshold
*/
static inline void mod_zone_state(struct zone *zone,
       enum zone_stat_item item, long delta, int overstep_mode)
{
        struct per_cpu_pageset __percpu *pcp = zone->pageset;
        s8 __percpu *p = pcp->vm_stat_diff + item;
        long o, n, t, z;

        do {
                z = 0;  /* overflow to zone counters */

                /*
                 * The fetching of the stat_threshold is racy. We may apply
                 * a counter threshold to the wrong the cpu if we get
                 * rescheduled while executing here. However, the next
                 * counter update will apply the threshold again and
                 * therefore bring the counter under the threshold again.
                 *
                 * Most of the time the thresholds are the same anyways
                 * for all cpus in a zone.
                 */
                t = this_cpu_read(pcp->stat_threshold);

                o = this_cpu_read(*p);
                n = delta + o;

                if (n > t || n < -t) {
                        int os = overstep_mode * (t >> 1) ;

                        /* Overflow must be added to zone counters */
                        z = n + os;
                        n = -os;
                }
        } while (this_cpu_cmpxchg(*p, o, n) != o);

        if (z)
                zone_page_state_add(z, zone, item);
}

void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
                         long delta)
{
        mod_zone_state(zone, item, delta, 0);
}
EXPORT_SYMBOL(mod_zone_page_state);

void inc_zone_page_state(struct page *page, enum zone_stat_item item)
{
        mod_zone_state(page_zone(page), item, 1, 1);
}
EXPORT_SYMBOL(inc_zone_page_state);

void dec_zone_page_state(struct page *page, enum zone_stat_item item)
{
        mod_zone_state(page_zone(page), item, -1, -1);
}
EXPORT_SYMBOL(dec_zone_page_state);

static inline void mod_node_state(struct pglist_data *pgdat,
       enum node_stat_item item, int delta, int overstep_mode)
{
        struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
        s8 __percpu *p = pcp->vm_node_stat_diff + item;
        long o, n, t, z;

        do {
                z = 0;  /* overflow to node counters */

                /*
                 * The fetching of the stat_threshold is racy. We may apply
                 * a counter threshold to the wrong the cpu if we get
                 * rescheduled while executing here. However, the next
                 * counter update will apply the threshold again and
                 * therefore bring the counter under the threshold again.
                 *
                 * Most of the time the thresholds are the same anyways
                 * for all cpus in a node.
                 */
                t = this_cpu_read(pcp->stat_threshold);

                o = this_cpu_read(*p);
                n = delta + o;

                if (n > t || n < -t) {
                        int os = overstep_mode * (t >> 1) ;

                        /* Overflow must be added to node counters */
                        z = n + os;
                        n = -os;
                }
        } while (this_cpu_cmpxchg(*p, o, n) != o);

        if (z)
                node_page_state_add(z, pgdat, item);
}

void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
                                        long delta)
{
        mod_node_state(pgdat, item, delta, 0);
}
EXPORT_SYMBOL(mod_node_page_state);

void inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
{
        mod_node_state(pgdat, item, 1, 1);
}

void inc_node_page_state(struct page *page, enum node_stat_item item)
{
        mod_node_state(page_pgdat(page), item, 1, 1);
}
EXPORT_SYMBOL(inc_node_page_state);

void dec_node_page_state(struct page *page, enum node_stat_item item)
{
        mod_node_state(page_pgdat(page), item, -1, -1);
}
EXPORT_SYMBOL(dec_node_page_state);
#else
/*
 * Use interrupt disable to serialize counter updates
 */
void mod_zone_page_state(struct zone *zone, enum zone_stat_item item,
                         long 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);

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);

void inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
{
        unsigned long flags;

        local_irq_save(flags);
        __inc_node_state(pgdat, item);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(inc_node_state);

void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
                                        long delta)
{
        unsigned long flags;

        local_irq_save(flags);
        __mod_node_page_state(pgdat, item, delta);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(mod_node_page_state);

void inc_node_page_state(struct page *page, enum node_stat_item item)
{
        unsigned long flags;
        struct pglist_data *pgdat;

        pgdat = page_pgdat(page);
        local_irq_save(flags);
        __inc_node_state(pgdat, item);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(inc_node_page_state);

void dec_node_page_state(struct page *page, enum node_stat_item item)
{
        unsigned long flags;

        local_irq_save(flags);
        __dec_node_page_state(page, item);
        local_irq_restore(flags);
}
EXPORT_SYMBOL(dec_node_page_state);
#endif

/*
 * Fold a differential into the global counters.
 * Returns the number of counters updated.
 */
static int fold_diff(int *zone_diff, int *node_diff)
{
        int i;
        int changes = 0;

        for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
                if (zone_diff[i]) {
                        atomic_long_add(zone_diff[i], &vm_zone_stat[i]);
                        changes++;
        }

        for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
                if (node_diff[i]) {
                        atomic_long_add(node_diff[i], &vm_node_stat[i]);
                        changes++;
        }
        return changes;
}

/*
 * Update the zone counters for 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.
 *
 * The function returns the number of global counters updated.
 */
static int refresh_cpu_vm_stats(bool do_pagesets)
{
        struct pglist_data *pgdat;
        struct zone *zone;
        int i;
        int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
        int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };
        int changes = 0;

        for_each_populated_zone(zone) {
                struct per_cpu_pageset __percpu *p = zone->pageset;

                for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
                        int v;

                        v = this_cpu_xchg(p->vm_stat_diff[i], 0);
                        if (v) {

                                atomic_long_add(v, &zone->vm_stat[i]);
                                global_zone_diff[i] += v;
#ifdef CONFIG_NUMA
                                /* 3 seconds idle till flush */
                                __this_cpu_write(p->expire, 3);
#endif
                        }
                }
#ifdef CONFIG_NUMA
                if (do_pagesets) {
                        cond_resched();
                        /*
                         * 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 (!__this_cpu_read(p->expire) ||
                               !__this_cpu_read(p->pcp.count))
                                continue;

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

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

                        if (__this_cpu_read(p->pcp.count)) {
                                drain_zone_pages(zone, this_cpu_ptr(&p->pcp));
                                changes++;
                        }
                }
#endif
        }

        for_each_online_pgdat(pgdat) {
                struct per_cpu_nodestat __percpu *p = pgdat->per_cpu_nodestats;

                for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) {
                        int v;

                        v = this_cpu_xchg(p->vm_node_stat_diff[i], 0);
                        if (v) {
                                atomic_long_add(v, &pgdat->vm_stat[i]);
                                global_node_diff[i] += v;
                        }
                }
        }

        changes += fold_diff(global_zone_diff, global_node_diff);
        return changes;
}

/*
 * Fold the data for an offline cpu into the global array.
 * There cannot be any access by the offline cpu and therefore
 * synchronization is simplified.
 */
void cpu_vm_stats_fold(int cpu)
{
        struct pglist_data *pgdat;
        struct zone *zone;
        int i;
        int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, };
        int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, };

        for_each_populated_zone(zone) {
                struct per_cpu_pageset *p;

                p = per_cpu_ptr(zone->pageset, cpu);

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

                                v = p->vm_stat_diff[i];
                                p->vm_stat_diff[i] = 0;
                                atomic_long_add(v, &zone->vm_stat[i]);
                                global_zone_diff[i] += v;
                        }
        }

        for_each_online_pgdat(pgdat) {
                struct per_cpu_nodestat *p;

                p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu);

                for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
                        if (p->vm_node_stat_diff[i]) {
                                int v;

                                v = p->vm_node_stat_diff[i];
                                p->vm_node_stat_diff[i] = 0;
                                atomic_long_add(v, &pgdat->vm_stat[i]);
                                global_node_diff[i] += v;
                        }
        }

        fold_diff(global_zone_diff, global_node_diff);
}

/*
 * this is only called if !populated_zone(zone), which implies no other users of
 * pset->vm_stat_diff[] exsist.
 */
void drain_zonestat(struct zone *zone, struct per_cpu_pageset *pset)
{
        int i;

        for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
                if (pset->vm_stat_diff[i]) {
                        int v = pset->vm_stat_diff[i];
                        pset->vm_stat_diff[i] = 0;
                        atomic_long_add(v, &zone->vm_stat[i]);
                        atomic_long_add(v, &vm_zone_stat[i]);
                }
}
#endif

#ifdef CONFIG_NUMA
/*
 * Determine the per node value of a stat item. This function
 * is called frequently in a NUMA machine, so try to be as
 * frugal as possible.
 */
unsigned long sum_zone_node_page_state(int node,
                                 enum zone_stat_item item)
{
        struct zone *zones = NODE_DATA(node)->node_zones;
        int i;
        unsigned long count = 0;

        for (i = 0; i < MAX_NR_ZONES; i++)
                count += zone_page_state(zones + i, item);

        return count;
}

/*
 * Determine the per node value of a stat item.
 */
unsigned long node_page_state(struct pglist_data *pgdat,
                                enum node_stat_item item)
{
        long x = atomic_long_read(&pgdat->vm_stat[item]);
#ifdef CONFIG_SMP
        if (x < 0)
                x = 0;
#endif
        return x;
}
#endif

#ifdef CONFIG_COMPACTION

struct contig_page_info {
        unsigned long free_pages;
        unsigned long free_blocks_total;
        unsigned long free_blocks_suitable;
};

/*
 * Calculate the number of free pages in a zone, how many contiguous
 * pages are free and how many are large enough to satisfy an allocation of
 * the target size. Note that this function makes no attempt to estimate
 * how many suitable free blocks there *might* be if MOVABLE pages were
 * migrated. Calculating that is possible, but expensive and can be
 * figured out from userspace
 */
static void fill_contig_page_info(struct zone *zone,
                                unsigned int suitable_order,
                                struct contig_page_info *info)
{
        unsigned int order;

        info->free_pages = 0;
        info->free_blocks_total = 0;
        info->free_blocks_suitable = 0;

        for (order = 0; order < MAX_ORDER; order++) {
                unsigned long blocks;

                /* Count number of free blocks */
                blocks = zone->free_area[order].nr_free;
                info->free_blocks_total += blocks;

                /* Count free base pages */
                info->free_pages += blocks << order;

                /* Count the suitable free blocks */
                if (order >= suitable_order)
                        info->free_blocks_suitable += blocks <<
                                                (order - suitable_order);
        }
}

/*
 * A fragmentation index only makes sense if an allocation of a requested
 * size would fail. If that is true, the fragmentation index indicates
 * whether external fragmentation or a lack of memory was the problem.
 * The value can be used to determine if page reclaim or compaction
 * should be used
 */
static int __fragmentation_index(unsigned int order, struct contig_page_info *info)
{
        unsigned long requested = 1UL << order;

        if (!info->free_blocks_total)
                return 0;

        /* Fragmentation index only makes sense when a request would fail */
        if (info->free_blocks_suitable)
                return -1000;

        /*
         * Index is between 0 and 1 so return within 3 decimal places
         *
         * 0 => allocation would fail due to lack of memory
         * 1 => allocation would fail due to fragmentation
         */
        return 1000 - div_u64( (1000+(div_u64(info->free_pages * 1000ULL, requested))), info->free_blocks_total);
}

/* Same as __fragmentation index but allocs contig_page_info on stack */
int fragmentation_index(struct zone *zone, unsigned int order)
{
        struct contig_page_info info;

        fill_contig_page_info(zone, order, &info);
        return __fragmentation_index(order, &info);
}
#endif

#if defined(CONFIG_PROC_FS) || defined(CONFIG_SYSFS) || defined(CONFIG_NUMA)
#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",

const char * const vmstat_text[] = {
        /* enum zone_stat_item countes */
        "nr_free_pages",
        "nr_zone_inactive_anon",
        "nr_zone_active_anon",
        "nr_zone_inactive_file",
        "nr_zone_active_file",
        "nr_zone_unevictable",
        "nr_zone_write_pending",
        "nr_mlock",
        "nr_page_table_pages",
        "nr_kernel_stack",
        "nr_bounce",
#if IS_ENABLED(CONFIG_ZSMALLOC)
        "nr_zspages",
#endif
#ifdef CONFIG_NUMA
        "numa_hit",
        "numa_miss",
        "numa_foreign",
        "numa_interleave",
        "numa_local",
        "numa_other",
#endif
        "nr_free_cma",

        /* Node-based counters */
        "nr_inactive_anon",
        "nr_active_anon",
        "nr_inactive_file",
        "nr_active_file",
        "nr_unevictable",
        "nr_slab_reclaimable",
        "nr_slab_unreclaimable",
        "nr_isolated_anon",
        "nr_isolated_file",
        "workingset_refault",
        "workingset_activate",
        "workingset_nodereclaim",
        "nr_anon_pages",
        "nr_mapped",
        "nr_file_pages",
        "nr_dirty",
        "nr_writeback",
        "nr_writeback_temp",
        "nr_shmem",
        "nr_shmem_hugepages",
        "nr_shmem_pmdmapped",
        "nr_anon_transparent_hugepages",
        "nr_unstable",
        "nr_vmscan_write",
        "nr_vmscan_immediate_reclaim",
        "nr_dirtied",
        "nr_written",

        /* enum writeback_stat_item counters */
        "nr_dirty_threshold",
        "nr_dirty_background_threshold",

#ifdef CONFIG_VM_EVENT_COUNTERS
        /* enum vm_event_item counters */
        "pgpgin",
        "pgpgout",
        "pswpin",
        "pswpout",

        TEXTS_FOR_ZONES("pgalloc")
        TEXTS_FOR_ZONES("allocstall")
        TEXTS_FOR_ZONES("pgskip")

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

        "pgfault",
        "pgmajfault",
        "pglazyfreed",

        "pgrefill",
        "pgsteal_kswapd",
        "pgsteal_direct",
        "pgscan_kswapd",
        "pgscan_direct",
        "pgscan_direct_throttle",

#ifdef CONFIG_NUMA
        "zone_reclaim_failed",
#endif
        "pginodesteal",
        "slabs_scanned",
        "kswapd_inodesteal",
        "kswapd_low_wmark_hit_quickly",
        "kswapd_high_wmark_hit_quickly",
        "pageoutrun",

        "pgrotated",

        "drop_pagecache",
        "drop_slab",
        "oom_kill",

#ifdef CONFIG_NUMA_BALANCING
        "numa_pte_updates",
        "numa_huge_pte_updates",
        "numa_hint_faults",
        "numa_hint_faults_local",
        "numa_pages_migrated",
#endif
#ifdef CONFIG_MIGRATION
        "pgmigrate_success",
        "pgmigrate_fail",
#endif
#ifdef CONFIG_COMPACTION
        "compact_migrate_scanned",
        "compact_free_scanned",
        "compact_isolated",
        "compact_stall",
        "compact_fail",
        "compact_success",
        "compact_daemon_wake",
        "compact_daemon_migrate_scanned",
        "compact_daemon_free_scanned",
#endif

#ifdef CONFIG_HUGETLB_PAGE
        "htlb_buddy_alloc_success",
        "htlb_buddy_alloc_fail",
#endif
        "unevictable_pgs_culled",
        "unevictable_pgs_scanned",
        "unevictable_pgs_rescued",
        "unevictable_pgs_mlocked",
        "unevictable_pgs_munlocked",
        "unevictable_pgs_cleared",
        "unevictable_pgs_stranded",

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        "thp_fault_alloc",
        "thp_fault_fallback",
        "thp_collapse_alloc",
        "thp_collapse_alloc_failed",
        "thp_file_alloc",
        "thp_file_mapped",
        "thp_split_page",
        "thp_split_page_failed",
        "thp_deferred_split_page",
        "thp_split_pmd",
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
        "thp_split_pud",
#endif
        "thp_zero_page_alloc",
        "thp_zero_page_alloc_failed",
#endif
#ifdef CONFIG_MEMORY_BALLOON
        "balloon_inflate",
        "balloon_deflate",
#ifdef CONFIG_BALLOON_COMPACTION
        "balloon_migrate",
#endif
#endif /* CONFIG_MEMORY_BALLOON */
#ifdef CONFIG_DEBUG_TLBFLUSH
#ifdef CONFIG_SMP
        "nr_tlb_remote_flush",
        "nr_tlb_remote_flush_received",
#endif /* CONFIG_SMP */
        "nr_tlb_local_flush_all",
        "nr_tlb_local_flush_one",
#endif /* CONFIG_DEBUG_TLBFLUSH */

#ifdef CONFIG_DEBUG_VM_VMACACHE
        "vmacache_find_calls",
        "vmacache_find_hits",
        "vmacache_full_flushes",
#endif
#endif /* CONFIG_VM_EVENTS_COUNTERS */
};
#endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA */


#if (defined(CONFIG_DEBUG_FS) && defined(CONFIG_COMPACTION)) || \
     defined(CONFIG_PROC_FS)
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 zones in a node and print using a callback.
 * If @assert_populated is true, only use callback for zones that are populated.
 */
static void walk_zones_in_node(struct seq_file *m, pg_data_t *pgdat,
                bool assert_populated, bool nolock,
                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 (assert_populated && !populated_zone(zone))
                        continue;

                if (!nolock)
                        spin_lock_irqsave(&zone->lock, flags);
                print(m, pgdat, zone);
                if (!nolock)
                        spin_unlock_irqrestore(&zone->lock, flags);
        }
}
#endif

#ifdef CONFIG_PROC_FS
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, true, false, 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, true, false, 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 = zone_end_pfn(zone);
        unsigned long count[MIGRATE_TYPES] = { 0, };

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

                page = pfn_to_online_page(pfn);
                if (!page)
                        continue;

                /* Watch for unexpected holes punched in the memmap */
                if (!memmap_valid_within(pfn, page, zone))
                        continue;

                if (page_zone(page) != zone)
                        continue;

                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, true, false,
                pagetypeinfo_showblockcount_print);

        return 0;
}

/*
 * Print out the number of pageblocks for each migratetype that contain pages
 * of other types. This gives an indication of how well fallbacks are being
 * contained by rmqueue_fallback(). It requires information from PAGE_OWNER
 * to determine what is going on
 */
static void pagetypeinfo_showmixedcount(struct seq_file *m, pg_data_t *pgdat)
{
#ifdef CONFIG_PAGE_OWNER
        int mtype;

        if (!static_branch_unlikely(&page_owner_inited))
                return;

        drain_all_pages(NULL);

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

        walk_zones_in_node(m, pgdat, true, true,
                pagetypeinfo_showmixedcount_print);
#endif /* CONFIG_PAGE_OWNER */
}

/*
 * 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_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);
        pagetypeinfo_showmixedcount(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 buddyinfo_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_operations = {
        .open           = pagetypeinfo_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

static bool is_zone_first_populated(pg_data_t *pgdat, struct zone *zone)
{
        int zid;

        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                struct zone *compare = &pgdat->node_zones[zid];

                if (populated_zone(compare))
                        return zone == compare;
        }

        return false;
}

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);
        if (is_zone_first_populated(pgdat, zone)) {
                seq_printf(m, "\n  per-node stats");
                for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) {
                        seq_printf(m, "\n      %-12s %lu",
                                vmstat_text[i + NR_VM_ZONE_STAT_ITEMS],
                                node_page_state(pgdat, i));
                }
        }
        seq_printf(m,
                   "\n  pages free     %lu"
                   "\n        min      %lu"
                   "\n        low      %lu"
                   "\n        high     %lu"
                   "\n        spanned  %lu"
                   "\n        present  %lu"
                   "\n        managed  %lu",
                   zone_page_state(zone, NR_FREE_PAGES),
                   min_wmark_pages(zone),
                   low_wmark_pages(zone),
                   high_wmark_pages(zone),
                   zone->spanned_pages,
                   zone->present_pages,
                   zone->managed_pages);

        seq_printf(m,
                   "\n        protection: (%ld",
                   zone->lowmem_reserve[0]);
        for (i = 1; i < ARRAY_SIZE(zone->lowmem_reserve); i++)
                seq_printf(m, ", %ld", zone->lowmem_reserve[i]);
        seq_putc(m, ')');

        /* If unpopulated, no other information is useful */
        if (!populated_zone(zone)) {
                seq_putc(m, '\n');
                return;
        }

        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  pagesets");
        for_each_online_cpu(i) {
                struct per_cpu_pageset *pageset;

                pageset = per_cpu_ptr(zone->pageset, 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  node_unreclaimable:  %u"
                   "\n  start_pfn:           %lu"
                   "\n  node_inactive_ratio: %u",
                   pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES,
                   zone->zone_start_pfn,
                   zone->zone_pgdat->inactive_ratio);
        seq_putc(m, '\n');
}

/*
 * Output information about zones in @pgdat.  All zones are printed regardless
 * of whether they are populated or not: lowmem_reserve_ratio operates on the
 * set of all zones and userspace would not be aware of such zones if they are
 * suppressed here (zoneinfo displays the effect of lowmem_reserve_ratio).
 */
static int zoneinfo_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = (pg_data_t *)arg;
        walk_zones_in_node(m, pgdat, false, false, 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 zoneinfo_file_operations = {
        .open           = zoneinfo_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

enum writeback_stat_item {
        NR_DIRTY_THRESHOLD,
        NR_DIRTY_BG_THRESHOLD,
        NR_VM_WRITEBACK_STAT_ITEMS,
};

static void *vmstat_start(struct seq_file *m, loff_t *pos)
{
        unsigned long *v;
        int i, stat_items_size;

        if (*pos >= ARRAY_SIZE(vmstat_text))
                return NULL;
        stat_items_size = NR_VM_ZONE_STAT_ITEMS * sizeof(unsigned long) +
                          NR_VM_NODE_STAT_ITEMS * sizeof(unsigned long) +
                          NR_VM_WRITEBACK_STAT_ITEMS * sizeof(unsigned long);

#ifdef CONFIG_VM_EVENT_COUNTERS
        stat_items_size += sizeof(struct vm_event_state);
#endif

        v = kmalloc(stat_items_size, GFP_KERNEL);
        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);
        v += NR_VM_ZONE_STAT_ITEMS;

        for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
                v[i] = global_node_page_state(i);
        v += NR_VM_NODE_STAT_ITEMS;

        global_dirty_limits(v + NR_DIRTY_BG_THRESHOLD,
                            v + NR_DIRTY_THRESHOLD);
        v += NR_VM_WRITEBACK_STAT_ITEMS;

#ifdef CONFIG_VM_EVENT_COUNTERS
        all_vm_events(v);
        v[PGPGIN] /= 2;         /* sectors -> kbytes */
        v[PGPGOUT] /= 2;
#endif
        return (unsigned long *)m->private + *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_puts(m, vmstat_text[off]);
        seq_put_decimal_ull(m, " ", *l);
        seq_putc(m, '\n');
        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 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;

#ifdef CONFIG_PROC_FS
static void refresh_vm_stats(struct work_struct *work)
{
        refresh_cpu_vm_stats(true);
}

int vmstat_refresh(struct ctl_table *table, int write,
                   void __user *buffer, size_t *lenp, loff_t *ppos)
{
        long val;
        int err;
        int i;

        /*
         * The regular update, every sysctl_stat_interval, may come later
         * than expected: leaving a significant amount in per_cpu buckets.
         * This is particularly misleading when checking a quantity of HUGE
         * pages, immediately after running a test.  /proc/sys/vm/stat_refresh,
         * which can equally be echo'ed to or cat'ted from (by root),
         * can be used to update the stats just before reading them.
         *
         * Oh, and since global_page_state() etc. are so careful to hide
         * transiently negative values, report an error here if any of
         * the stats is negative, so we know to go looking for imbalance.
         */
        err = schedule_on_each_cpu(refresh_vm_stats);
        if (err)
                return err;
        for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
                val = atomic_long_read(&vm_zone_stat[i]);
                if (val < 0) {
                        pr_warn("%s: %s %ld\n",
                                __func__, vmstat_text[i], val);
                        err = -EINVAL;
                }
        }
        if (err)
                return err;
        if (write)
                *ppos += *lenp;
        else
                *lenp = 0;
        return 0;
}
#endif /* CONFIG_PROC_FS */

static void vmstat_update(struct work_struct *w)
{
        if (refresh_cpu_vm_stats(true)) {
                /*
                 * Counters were updated so we expect more updates
                 * to occur in the future. Keep on running the
                 * update worker thread.
                 */
                queue_delayed_work_on(smp_processor_id(), mm_percpu_wq,
                                this_cpu_ptr(&vmstat_work),
                                round_jiffies_relative(sysctl_stat_interval));
        }
}

/*
 * Switch off vmstat processing and then fold all the remaining differentials
 * until the diffs stay at zero. The function is used by NOHZ and can only be
 * invoked when tick processing is not active.
 */
/*
 * Check if the diffs for a certain cpu indicate that
 * an update is needed.
 */
static bool need_update(int cpu)
{
        struct zone *zone;

        for_each_populated_zone(zone) {
                struct per_cpu_pageset *p = per_cpu_ptr(zone->pageset, cpu);

                BUILD_BUG_ON(sizeof(p->vm_stat_diff[0]) != 1);
                /*
                 * The fast way of checking if there are any vmstat diffs.
                 * This works because the diffs are byte sized items.
                 */
                if (memchr_inv(p->vm_stat_diff, 0, NR_VM_ZONE_STAT_ITEMS))
                        return true;

        }
        return false;
}

/*
 * Switch off vmstat processing and then fold all the remaining differentials
 * until the diffs stay at zero. The function is used by NOHZ and can only be
 * invoked when tick processing is not active.
 */
void quiet_vmstat(void)
{
        if (system_state != SYSTEM_RUNNING)
                return;

        if (!delayed_work_pending(this_cpu_ptr(&vmstat_work)))
                return;

        if (!need_update(smp_processor_id()))
                return;

        /*
         * Just refresh counters and do not care about the pending delayed
         * vmstat_update. It doesn't fire that often to matter and canceling
         * it would be too expensive from this path.
         * vmstat_shepherd will take care about that for us.
         */
        refresh_cpu_vm_stats(false);
}

/*
 * Shepherd worker thread that checks the
 * differentials of processors that have their worker
 * threads for vm statistics updates disabled because of
 * inactivity.
 */
static void vmstat_shepherd(struct work_struct *w);

static DECLARE_DEFERRABLE_WORK(shepherd, vmstat_shepherd);

static void vmstat_shepherd(struct work_struct *w)
{
        int cpu;

        get_online_cpus();
        /* Check processors whose vmstat worker threads have been disabled */
        for_each_online_cpu(cpu) {
                struct delayed_work *dw = &per_cpu(vmstat_work, cpu);

                if (!delayed_work_pending(dw) && need_update(cpu))
                        queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0);
        }
        put_online_cpus();

        schedule_delayed_work(&shepherd,
                round_jiffies_relative(sysctl_stat_interval));
}

static void __init start_shepherd_timer(void)
{
        int cpu;

        for_each_possible_cpu(cpu)
                INIT_DEFERRABLE_WORK(per_cpu_ptr(&vmstat_work, cpu),
                        vmstat_update);

        schedule_delayed_work(&shepherd,
                round_jiffies_relative(sysctl_stat_interval));
}

static void __init init_cpu_node_state(void)
{
        int node;

        for_each_online_node(node) {
                if (cpumask_weight(cpumask_of_node(node)) > 0)
                        node_set_state(node, N_CPU);
        }
}

static int vmstat_cpu_online(unsigned int cpu)
{
        refresh_zone_stat_thresholds();
        node_set_state(cpu_to_node(cpu), N_CPU);
        return 0;
}

static int vmstat_cpu_down_prep(unsigned int cpu)
{
        cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
        return 0;
}

static int vmstat_cpu_dead(unsigned int cpu)
{
        const struct cpumask *node_cpus;
        int node;

        node = cpu_to_node(cpu);

        refresh_zone_stat_thresholds();
        node_cpus = cpumask_of_node(node);
        if (cpumask_weight(node_cpus) > 0)
                return 0;

        node_clear_state(node, N_CPU);
        return 0;
}

#endif

struct workqueue_struct *mm_percpu_wq;

void __init init_mm_internals(void)
{
        int ret __maybe_unused;

        mm_percpu_wq = alloc_workqueue("mm_percpu_wq", WQ_MEM_RECLAIM, 0);

#ifdef CONFIG_SMP
        ret = cpuhp_setup_state_nocalls(CPUHP_MM_VMSTAT_DEAD, "mm/vmstat:dead",
                                        NULL, vmstat_cpu_dead);
        if (ret < 0)
                pr_err("vmstat: failed to register 'dead' hotplug state\n");

        ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "mm/vmstat:online",
                                        vmstat_cpu_online,
                                        vmstat_cpu_down_prep);
        if (ret < 0)
                pr_err("vmstat: failed to register 'online' hotplug state\n");

        get_online_cpus();
        init_cpu_node_state();
        put_online_cpus();

        start_shepherd_timer();
#endif
#ifdef CONFIG_PROC_FS
        proc_create("buddyinfo", 0444, NULL, &buddyinfo_file_operations);
        proc_create("pagetypeinfo", 0444, NULL, &pagetypeinfo_file_operations);
        proc_create("vmstat", 0444, NULL, &vmstat_file_operations);
        proc_create("zoneinfo", 0444, NULL, &zoneinfo_file_operations);
#endif
}

#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_COMPACTION)

/*
 * Return an index indicating how much of the available free memory is
 * unusable for an allocation of the requested size.
 */
static int unusable_free_index(unsigned int order,
                                struct contig_page_info *info)
{
        /* No free memory is interpreted as all free memory is unusable */
        if (info->free_pages == 0)
                return 1000;

        /*
         * Index should be a value between 0 and 1. Return a value to 3
         * decimal places.
         *
         * 0 => no fragmentation
         * 1 => high fragmentation
         */
        return div_u64((info->free_pages - (info->free_blocks_suitable << order)) * 1000ULL, info->free_pages);

}

static void unusable_show_print(struct seq_file *m,
                                        pg_data_t *pgdat, struct zone *zone)
{
        unsigned int order;
        int index;
        struct contig_page_info info;

        seq_printf(m, "Node %d, zone %8s ",
                                pgdat->node_id,
                                zone->name);
        for (order = 0; order < MAX_ORDER; ++order) {
                fill_contig_page_info(zone, order, &info);
                index = unusable_free_index(order, &info);
                seq_printf(m, "%d.%03d ", index / 1000, index % 1000);
        }

        seq_putc(m, '\n');
}

/*
 * Display unusable free space index
 *
 * The unusable free space index measures how much of the available free
 * memory cannot be used to satisfy an allocation of a given size and is a
 * value between 0 and 1. The higher the value, the more of free memory is
 * unusable and by implication, the worse the external fragmentation is. This
 * can be expressed as a percentage by multiplying by 100.
 */
static int unusable_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_MEMORY))
                return 0;

        walk_zones_in_node(m, pgdat, true, false, unusable_show_print);

        return 0;
}

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

static int unusable_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &unusable_op);
}

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

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

        /* Alloc on stack as interrupts are disabled for zone walk */
        struct contig_page_info info;

        seq_printf(m, "Node %d, zone %8s ",
                                pgdat->node_id,
                                zone->name);
        for (order = 0; order < MAX_ORDER; ++order) {
                fill_contig_page_info(zone, order, &info);
                index = __fragmentation_index(order, &info);
                seq_printf(m, "%d.%03d ", index / 1000, index % 1000);
        }

        seq_putc(m, '\n');
}

/*
 * Display fragmentation index for orders that allocations would fail for
 */
static int extfrag_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = (pg_data_t *)arg;

        walk_zones_in_node(m, pgdat, true, false, extfrag_show_print);

        return 0;
}

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

static int extfrag_open(struct inode *inode, struct file *file)
{
        return seq_open(file, &extfrag_op);
}

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

static int __init extfrag_debug_init(void)
{
        struct dentry *extfrag_debug_root;

        extfrag_debug_root = debugfs_create_dir("extfrag", NULL);
        if (!extfrag_debug_root)
                return -ENOMEM;

        if (!debugfs_create_file("unusable_index", 0444,
                        extfrag_debug_root, NULL, &unusable_file_ops))
                goto fail;

        if (!debugfs_create_file("extfrag_index", 0444,
                        extfrag_debug_root, NULL, &extfrag_file_ops))
                goto fail;

        return 0;
fail:
        debugfs_remove_recursive(extfrag_debug_root);
        return -ENOMEM;
}

module_init(extfrag_debug_init);
#endif