memcg: handle swap caches

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

/* memcontrol.c - Memory Controller
 *
 * Copyright IBM Corporation, 2007
 * Author Balbir Singh <balbir@linux.vnet.ibm.com>
 *
 * Copyright 2007 OpenVZ SWsoft Inc
 * Author: Pavel Emelianov <xemul@openvz.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/res_counter.h>
#include <linux/memcontrol.h>
#include <linux/cgroup.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/smp.h>
#include <linux/page-flags.h>
#include <linux/backing-dev.h>
#include <linux/bit_spinlock.h>
#include <linux/rcupdate.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/spinlock.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
#include <linux/mm_inline.h>
#include <linux/page_cgroup.h>

#include <asm/uaccess.h>

struct cgroup_subsys mem_cgroup_subsys __read_mostly;
#define MEM_CGROUP_RECLAIM_RETRIES      5

/*
 * Statistics for memory cgroup.
 */
enum mem_cgroup_stat_index {
        /*
         * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
         */
        MEM_CGROUP_STAT_CACHE,     /* # of pages charged as cache */
        MEM_CGROUP_STAT_RSS,       /* # of pages charged as rss */
        MEM_CGROUP_STAT_PGPGIN_COUNT,   /* # of pages paged in */
        MEM_CGROUP_STAT_PGPGOUT_COUNT,  /* # of pages paged out */

        MEM_CGROUP_STAT_NSTATS,
};

struct mem_cgroup_stat_cpu {
        s64 count[MEM_CGROUP_STAT_NSTATS];
} ____cacheline_aligned_in_smp;

struct mem_cgroup_stat {
        struct mem_cgroup_stat_cpu cpustat[0];
};

/*
 * For accounting under irq disable, no need for increment preempt count.
 */
static inline void __mem_cgroup_stat_add_safe(struct mem_cgroup_stat_cpu *stat,
                enum mem_cgroup_stat_index idx, int val)
{
        stat->count[idx] += val;
}

static s64 mem_cgroup_read_stat(struct mem_cgroup_stat *stat,
                enum mem_cgroup_stat_index idx)
{
        int cpu;
        s64 ret = 0;
        for_each_possible_cpu(cpu)
                ret += stat->cpustat[cpu].count[idx];
        return ret;
}

/*
 * per-zone information in memory controller.
 */
struct mem_cgroup_per_zone {
        /*
         * spin_lock to protect the per cgroup LRU
         */
        spinlock_t              lru_lock;
        struct list_head        lists[NR_LRU_LISTS];
        unsigned long           count[NR_LRU_LISTS];
};
/* Macro for accessing counter */
#define MEM_CGROUP_ZSTAT(mz, idx)       ((mz)->count[(idx)])

struct mem_cgroup_per_node {
        struct mem_cgroup_per_zone zoneinfo[MAX_NR_ZONES];
};

struct mem_cgroup_lru_info {
        struct mem_cgroup_per_node *nodeinfo[MAX_NUMNODES];
};

/*
 * The memory controller data structure. The memory controller controls both
 * page cache and RSS per cgroup. We would eventually like to provide
 * statistics based on the statistics developed by Rik Van Riel for clock-pro,
 * to help the administrator determine what knobs to tune.
 *
 * TODO: Add a water mark for the memory controller. Reclaim will begin when
 * we hit the water mark. May be even add a low water mark, such that
 * no reclaim occurs from a cgroup at it's low water mark, this is
 * a feature that will be implemented much later in the future.
 */
struct mem_cgroup {
        struct cgroup_subsys_state css;
        /*
         * the counter to account for memory usage
         */
        struct res_counter res;
        /*
         * Per cgroup active and inactive list, similar to the
         * per zone LRU lists.
         */
        struct mem_cgroup_lru_info info;

        int     prev_priority;  /* for recording reclaim priority */
        /*
         * statistics. This must be placed at the end of memcg.
         */
        struct mem_cgroup_stat stat;
};

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_MAPPED,
        MEM_CGROUP_CHARGE_TYPE_SHMEM,   /* used by page migration of shmem */
        MEM_CGROUP_CHARGE_TYPE_FORCE,   /* used by force_empty */
        MEM_CGROUP_CHARGE_TYPE_SWAPOUT, /* for accounting swapcache */
        NR_CHARGE_TYPE,
};

/* only for here (for easy reading.) */
#define PCGF_CACHE      (1UL << PCG_CACHE)
#define PCGF_USED       (1UL << PCG_USED)
#define PCGF_ACTIVE     (1UL << PCG_ACTIVE)
#define PCGF_LOCK       (1UL << PCG_LOCK)
#define PCGF_FILE       (1UL << PCG_FILE)
static const unsigned long
pcg_default_flags[NR_CHARGE_TYPE] = {
        PCGF_CACHE | PCGF_FILE | PCGF_USED | PCGF_LOCK, /* File Cache */
        PCGF_ACTIVE | PCGF_USED | PCGF_LOCK, /* Anon */
        PCGF_ACTIVE | PCGF_CACHE | PCGF_USED | PCGF_LOCK, /* Shmem */
        0, /* FORCE */
};

/*
 * Always modified under lru lock. Then, not necessary to preempt_disable()
 */
static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
                                         struct page_cgroup *pc,
                                         bool charge)
{
        int val = (charge)? 1 : -1;
        struct mem_cgroup_stat *stat = &mem->stat;
        struct mem_cgroup_stat_cpu *cpustat;

        VM_BUG_ON(!irqs_disabled());

        cpustat = &stat->cpustat[smp_processor_id()];
        if (PageCgroupCache(pc))
                __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_CACHE, val);
        else
                __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_RSS, val);

        if (charge)
                __mem_cgroup_stat_add_safe(cpustat,
                                MEM_CGROUP_STAT_PGPGIN_COUNT, 1);
        else
                __mem_cgroup_stat_add_safe(cpustat,
                                MEM_CGROUP_STAT_PGPGOUT_COUNT, 1);
}

static struct mem_cgroup_per_zone *
mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid)
{
        return &mem->info.nodeinfo[nid]->zoneinfo[zid];
}

static struct mem_cgroup_per_zone *
page_cgroup_zoneinfo(struct page_cgroup *pc)
{
        struct mem_cgroup *mem = pc->mem_cgroup;
        int nid = page_cgroup_nid(pc);
        int zid = page_cgroup_zid(pc);

        return mem_cgroup_zoneinfo(mem, nid, zid);
}

static unsigned long mem_cgroup_get_all_zonestat(struct mem_cgroup *mem,
                                        enum lru_list idx)
{
        int nid, zid;
        struct mem_cgroup_per_zone *mz;
        u64 total = 0;

        for_each_online_node(nid)
                for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                        mz = mem_cgroup_zoneinfo(mem, nid, zid);
                        total += MEM_CGROUP_ZSTAT(mz, idx);
                }
        return total;
}

static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
{
        return container_of(cgroup_subsys_state(cont,
                                mem_cgroup_subsys_id), struct mem_cgroup,
                                css);
}

struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
{
        /*
         * mm_update_next_owner() may clear mm->owner to NULL
         * if it races with swapoff, page migration, etc.
         * So this can be called with p == NULL.
         */
        if (unlikely(!p))
                return NULL;

        return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
                                struct mem_cgroup, css);
}

static void __mem_cgroup_remove_list(struct mem_cgroup_per_zone *mz,
                        struct page_cgroup *pc)
{
        int lru = LRU_BASE;

        if (PageCgroupUnevictable(pc))
                lru = LRU_UNEVICTABLE;
        else {
                if (PageCgroupActive(pc))
                        lru += LRU_ACTIVE;
                if (PageCgroupFile(pc))
                        lru += LRU_FILE;
        }

        MEM_CGROUP_ZSTAT(mz, lru) -= 1;

        mem_cgroup_charge_statistics(pc->mem_cgroup, pc, false);
        list_del(&pc->lru);
}

static void __mem_cgroup_add_list(struct mem_cgroup_per_zone *mz,
                                struct page_cgroup *pc, bool hot)
{
        int lru = LRU_BASE;

        if (PageCgroupUnevictable(pc))
                lru = LRU_UNEVICTABLE;
        else {
                if (PageCgroupActive(pc))
                        lru += LRU_ACTIVE;
                if (PageCgroupFile(pc))
                        lru += LRU_FILE;
        }

        MEM_CGROUP_ZSTAT(mz, lru) += 1;
        if (hot)
                list_add(&pc->lru, &mz->lists[lru]);
        else
                list_add_tail(&pc->lru, &mz->lists[lru]);

        mem_cgroup_charge_statistics(pc->mem_cgroup, pc, true);
}

static void __mem_cgroup_move_lists(struct page_cgroup *pc, enum lru_list lru)
{
        struct mem_cgroup_per_zone *mz = page_cgroup_zoneinfo(pc);
        int active    = PageCgroupActive(pc);
        int file      = PageCgroupFile(pc);
        int unevictable = PageCgroupUnevictable(pc);
        enum lru_list from = unevictable ? LRU_UNEVICTABLE :
                                (LRU_FILE * !!file + !!active);

        if (lru == from)
                return;

        MEM_CGROUP_ZSTAT(mz, from) -= 1;
        /*
         * However this is done under mz->lru_lock, another flags, which
         * are not related to LRU, will be modified from out-of-lock.
         * We have to use atomic set/clear flags.
         */
        if (is_unevictable_lru(lru)) {
                ClearPageCgroupActive(pc);
                SetPageCgroupUnevictable(pc);
        } else {
                if (is_active_lru(lru))
                        SetPageCgroupActive(pc);
                else
                        ClearPageCgroupActive(pc);
                ClearPageCgroupUnevictable(pc);
        }

        MEM_CGROUP_ZSTAT(mz, lru) += 1;
        list_move(&pc->lru, &mz->lists[lru]);
}

int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
{
        int ret;

        task_lock(task);
        ret = task->mm && mm_match_cgroup(task->mm, mem);
        task_unlock(task);
        return ret;
}

/*
 * This routine assumes that the appropriate zone's lru lock is already held
 */
void mem_cgroup_move_lists(struct page *page, enum lru_list lru)
{
        struct page_cgroup *pc;
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;

        if (mem_cgroup_subsys.disabled)
                return;

        /*
         * We cannot lock_page_cgroup while holding zone's lru_lock,
         * because other holders of lock_page_cgroup can be interrupted
         * with an attempt to rotate_reclaimable_page.  But we cannot
         * safely get to page_cgroup without it, so just try_lock it:
         * mem_cgroup_isolate_pages allows for page left on wrong list.
         */
        pc = lookup_page_cgroup(page);
        if (!trylock_page_cgroup(pc))
                return;
        if (pc && PageCgroupUsed(pc)) {
                mz = page_cgroup_zoneinfo(pc);
                spin_lock_irqsave(&mz->lru_lock, flags);
                __mem_cgroup_move_lists(pc, lru);
                spin_unlock_irqrestore(&mz->lru_lock, flags);
        }
        unlock_page_cgroup(pc);
}

/*
 * Calculate mapped_ratio under memory controller. This will be used in
 * vmscan.c for deteremining we have to reclaim mapped pages.
 */
int mem_cgroup_calc_mapped_ratio(struct mem_cgroup *mem)
{
        long total, rss;

        /*
         * usage is recorded in bytes. But, here, we assume the number of
         * physical pages can be represented by "long" on any arch.
         */
        total = (long) (mem->res.usage >> PAGE_SHIFT) + 1L;
        rss = (long)mem_cgroup_read_stat(&mem->stat, MEM_CGROUP_STAT_RSS);
        return (int)((rss * 100L) / total);
}

/*
 * prev_priority control...this will be used in memory reclaim path.
 */
int mem_cgroup_get_reclaim_priority(struct mem_cgroup *mem)
{
        return mem->prev_priority;
}

void mem_cgroup_note_reclaim_priority(struct mem_cgroup *mem, int priority)
{
        if (priority < mem->prev_priority)
                mem->prev_priority = priority;
}

void mem_cgroup_record_reclaim_priority(struct mem_cgroup *mem, int priority)
{
        mem->prev_priority = priority;
}

/*
 * Calculate # of pages to be scanned in this priority/zone.
 * See also vmscan.c
 *
 * priority starts from "DEF_PRIORITY" and decremented in each loop.
 * (see include/linux/mmzone.h)
 */

long mem_cgroup_calc_reclaim(struct mem_cgroup *mem, struct zone *zone,
                                        int priority, enum lru_list lru)
{
        long nr_pages;
        int nid = zone->zone_pgdat->node_id;
        int zid = zone_idx(zone);
        struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(mem, nid, zid);

        nr_pages = MEM_CGROUP_ZSTAT(mz, lru);

        return (nr_pages >> priority);
}

unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
                                        struct list_head *dst,
                                        unsigned long *scanned, int order,
                                        int mode, struct zone *z,
                                        struct mem_cgroup *mem_cont,
                                        int active, int file)
{
        unsigned long nr_taken = 0;
        struct page *page;
        unsigned long scan;
        LIST_HEAD(pc_list);
        struct list_head *src;
        struct page_cgroup *pc, *tmp;
        int nid = z->zone_pgdat->node_id;
        int zid = zone_idx(z);
        struct mem_cgroup_per_zone *mz;
        int lru = LRU_FILE * !!file + !!active;

        BUG_ON(!mem_cont);
        mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);
        src = &mz->lists[lru];

        spin_lock(&mz->lru_lock);
        scan = 0;
        list_for_each_entry_safe_reverse(pc, tmp, src, lru) {
                if (scan >= nr_to_scan)
                        break;
                if (unlikely(!PageCgroupUsed(pc)))
                        continue;
                page = pc->page;

                if (unlikely(!PageLRU(page)))
                        continue;

                /*
                 * TODO: play better with lumpy reclaim, grabbing anything.
                 */
                if (PageUnevictable(page) ||
                    (PageActive(page) && !active) ||
                    (!PageActive(page) && active)) {
                        __mem_cgroup_move_lists(pc, page_lru(page));
                        continue;
                }

                scan++;
                list_move(&pc->lru, &pc_list);

                if (__isolate_lru_page(page, mode, file) == 0) {
                        list_move(&page->lru, dst);
                        nr_taken++;
                }
        }

        list_splice(&pc_list, src);
        spin_unlock(&mz->lru_lock);

        *scanned = scan;
        return nr_taken;
}

/*
 * Unlike exported interface, "oom" parameter is added. if oom==true,
 * oom-killer can be invoked.
 */
static int __mem_cgroup_try_charge(struct mm_struct *mm,
                        gfp_t gfp_mask, struct mem_cgroup **memcg, bool oom)
{
        struct mem_cgroup *mem;
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        /*
         * We always charge the cgroup the mm_struct belongs to.
         * The mm_struct's mem_cgroup changes on task migration if the
         * thread group leader migrates. It's possible that mm is not
         * set, if so charge the init_mm (happens for pagecache usage).
         */
        if (likely(!*memcg)) {
                rcu_read_lock();
                mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
                if (unlikely(!mem)) {
                        rcu_read_unlock();
                        return 0;
                }
                /*
                 * For every charge from the cgroup, increment reference count
                 */
                css_get(&mem->css);
                *memcg = mem;
                rcu_read_unlock();
        } else {
                mem = *memcg;
                css_get(&mem->css);
        }


        while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE))) {
                if (!(gfp_mask & __GFP_WAIT))
                        goto nomem;

                if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
                        continue;

                /*
                 * try_to_free_mem_cgroup_pages() might not give us a full
                 * picture of reclaim. Some pages are reclaimed and might be
                 * moved to swap cache or just unmapped from the cgroup.
                 * Check the limit again to see if the reclaim reduced the
                 * current usage of the cgroup before giving up
                 */
                if (res_counter_check_under_limit(&mem->res))
                        continue;

                if (!nr_retries--) {
                        if (oom)
                                mem_cgroup_out_of_memory(mem, gfp_mask);
                        goto nomem;
                }
        }
        return 0;
nomem:
        css_put(&mem->css);
        return -ENOMEM;
}

/**
 * mem_cgroup_try_charge - get charge of PAGE_SIZE.
 * @mm: an mm_struct which is charged against. (when *memcg is NULL)
 * @gfp_mask: gfp_mask for reclaim.
 * @memcg: a pointer to memory cgroup which is charged against.
 *
 * charge against memory cgroup pointed by *memcg. if *memcg == NULL, estimated
 * memory cgroup from @mm is got and stored in *memcg.
 *
 * Returns 0 if success. -ENOMEM at failure.
 * This call can invoke OOM-Killer.
 */

int mem_cgroup_try_charge(struct mm_struct *mm,
                          gfp_t mask, struct mem_cgroup **memcg)
{
        return __mem_cgroup_try_charge(mm, mask, memcg, true);
}

/*
 * commit a charge got by mem_cgroup_try_charge() and makes page_cgroup to be
 * USED state. If already USED, uncharge and return.
 */

static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
                                     struct page_cgroup *pc,
                                     enum charge_type ctype)
{
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;

        /* try_charge() can return NULL to *memcg, taking care of it. */
        if (!mem)
                return;

        lock_page_cgroup(pc);
        if (unlikely(PageCgroupUsed(pc))) {
                unlock_page_cgroup(pc);
                res_counter_uncharge(&mem->res, PAGE_SIZE);
                css_put(&mem->css);
                return;
        }
        pc->mem_cgroup = mem;
        /*
         * If a page is accounted as a page cache, insert to inactive list.
         * If anon, insert to active list.
         */
        pc->flags = pcg_default_flags[ctype];

        mz = page_cgroup_zoneinfo(pc);

        spin_lock_irqsave(&mz->lru_lock, flags);
        __mem_cgroup_add_list(mz, pc, true);
        spin_unlock_irqrestore(&mz->lru_lock, flags);
        unlock_page_cgroup(pc);
}

/**
 * mem_cgroup_move_account - move account of the page
 * @pc: page_cgroup of the page.
 * @from: mem_cgroup which the page is moved from.
 * @to: mem_cgroup which the page is moved to. @from != @to.
 *
 * The caller must confirm following.
 * 1. disable irq.
 * 2. lru_lock of old mem_cgroup(@from) should be held.
 *
 * returns 0 at success,
 * returns -EBUSY when lock is busy or "pc" is unstable.
 *
 * This function does "uncharge" from old cgroup but doesn't do "charge" to
 * new cgroup. It should be done by a caller.
 */

static int mem_cgroup_move_account(struct page_cgroup *pc,
        struct mem_cgroup *from, struct mem_cgroup *to)
{
        struct mem_cgroup_per_zone *from_mz, *to_mz;
        int nid, zid;
        int ret = -EBUSY;

        VM_BUG_ON(!irqs_disabled());
        VM_BUG_ON(from == to);

        nid = page_cgroup_nid(pc);
        zid = page_cgroup_zid(pc);
        from_mz =  mem_cgroup_zoneinfo(from, nid, zid);
        to_mz =  mem_cgroup_zoneinfo(to, nid, zid);


        if (!trylock_page_cgroup(pc))
                return ret;

        if (!PageCgroupUsed(pc))
                goto out;

        if (pc->mem_cgroup != from)
                goto out;

        if (spin_trylock(&to_mz->lru_lock)) {
                __mem_cgroup_remove_list(from_mz, pc);
                css_put(&from->css);
                res_counter_uncharge(&from->res, PAGE_SIZE);
                pc->mem_cgroup = to;
                css_get(&to->css);
                __mem_cgroup_add_list(to_mz, pc, false);
                ret = 0;
                spin_unlock(&to_mz->lru_lock);
        }
out:
        unlock_page_cgroup(pc);
        return ret;
}

/*
 * move charges to its parent.
 */

static int mem_cgroup_move_parent(struct page_cgroup *pc,
                                  struct mem_cgroup *child,
                                  gfp_t gfp_mask)
{
        struct cgroup *cg = child->css.cgroup;
        struct cgroup *pcg = cg->parent;
        struct mem_cgroup *parent;
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;
        int ret;

        /* Is ROOT ? */
        if (!pcg)
                return -EINVAL;

        parent = mem_cgroup_from_cont(pcg);

        ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false);
        if (ret)
                return ret;

        mz = mem_cgroup_zoneinfo(child,
                        page_cgroup_nid(pc), page_cgroup_zid(pc));

        spin_lock_irqsave(&mz->lru_lock, flags);
        ret = mem_cgroup_move_account(pc, child, parent);
        spin_unlock_irqrestore(&mz->lru_lock, flags);

        /* drop extra refcnt */
        css_put(&parent->css);
        /* uncharge if move fails */
        if (ret)
                res_counter_uncharge(&parent->res, PAGE_SIZE);

        return ret;
}

/*
 * Charge the memory controller for page usage.
 * Return
 * 0 if the charge was successful
 * < 0 if the cgroup is over its limit
 */
static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask, enum charge_type ctype,
                                struct mem_cgroup *memcg)
{
        struct mem_cgroup *mem;
        struct page_cgroup *pc;
        int ret;

        pc = lookup_page_cgroup(page);
        /* can happen at boot */
        if (unlikely(!pc))
                return 0;
        prefetchw(pc);

        mem = memcg;
        ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, true);
        if (ret)
                return ret;

        __mem_cgroup_commit_charge(mem, pc, ctype);
        return 0;
}

int mem_cgroup_newpage_charge(struct page *page,
                              struct mm_struct *mm, gfp_t gfp_mask)
{
        if (mem_cgroup_subsys.disabled)
                return 0;
        if (PageCompound(page))
                return 0;
        /*
         * If already mapped, we don't have to account.
         * If page cache, page->mapping has address_space.
         * But page->mapping may have out-of-use anon_vma pointer,
         * detecit it by PageAnon() check. newly-mapped-anon's page->mapping
         * is NULL.
         */
        if (page_mapped(page) || (page->mapping && !PageAnon(page)))
                return 0;
        if (unlikely(!mm))
                mm = &init_mm;
        return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
}

int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
{
        if (mem_cgroup_subsys.disabled)
                return 0;
        if (PageCompound(page))
                return 0;
        /*
         * Corner case handling. This is called from add_to_page_cache()
         * in usual. But some FS (shmem) precharges this page before calling it
         * and call add_to_page_cache() with GFP_NOWAIT.
         *
         * For GFP_NOWAIT case, the page may be pre-charged before calling
         * add_to_page_cache(). (See shmem.c) check it here and avoid to call
         * charge twice. (It works but has to pay a bit larger cost.)
         */
        if (!(gfp_mask & __GFP_WAIT)) {
                struct page_cgroup *pc;


                pc = lookup_page_cgroup(page);
                if (!pc)
                        return 0;
                lock_page_cgroup(pc);
                if (PageCgroupUsed(pc)) {
                        unlock_page_cgroup(pc);
                        return 0;
                }
                unlock_page_cgroup(pc);
        }

        if (unlikely(!mm))
                mm = &init_mm;

        if (page_is_file_cache(page))
                return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_CACHE, NULL);
        else
                return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
}

#ifdef CONFIG_SWAP
int mem_cgroup_cache_charge_swapin(struct page *page,
                        struct mm_struct *mm, gfp_t mask, bool locked)
{
        int ret = 0;

        if (mem_cgroup_subsys.disabled)
                return 0;
        if (unlikely(!mm))
                mm = &init_mm;
        if (!locked)
                lock_page(page);
        /*
         * If not locked, the page can be dropped from SwapCache until
         * we reach here.
         */
        if (PageSwapCache(page)) {
                ret = mem_cgroup_charge_common(page, mm, mask,
                                MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
        }
        if (!locked)
                unlock_page(page);

        return ret;
}
#endif

void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
{
        struct page_cgroup *pc;

        if (mem_cgroup_subsys.disabled)
                return;
        if (!ptr)
                return;
        pc = lookup_page_cgroup(page);
        __mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
{
        if (mem_cgroup_subsys.disabled)
                return;
        if (!mem)
                return;
        res_counter_uncharge(&mem->res, PAGE_SIZE);
        css_put(&mem->css);
}


/*
 * uncharge if !page_mapped(page)
 */
static void
__mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
{
        struct page_cgroup *pc;
        struct mem_cgroup *mem;
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;

        if (mem_cgroup_subsys.disabled)
                return;

        if (PageSwapCache(page))
                return;

        /*
         * Check if our page_cgroup is valid
         */
        pc = lookup_page_cgroup(page);
        if (unlikely(!pc || !PageCgroupUsed(pc)))
                return;

        lock_page_cgroup(pc);

        if (!PageCgroupUsed(pc))
                goto unlock_out;

        switch (ctype) {
        case MEM_CGROUP_CHARGE_TYPE_MAPPED:
                if (page_mapped(page))
                        goto unlock_out;
                break;
        case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
                if (!PageAnon(page)) {  /* Shared memory */
                        if (page->mapping && !page_is_file_cache(page))
                                goto unlock_out;
                } else if (page_mapped(page)) /* Anon */
                                goto unlock_out;
                break;
        default:
                break;
        }

        ClearPageCgroupUsed(pc);
        mem = pc->mem_cgroup;

        mz = page_cgroup_zoneinfo(pc);
        spin_lock_irqsave(&mz->lru_lock, flags);
        __mem_cgroup_remove_list(mz, pc);
        spin_unlock_irqrestore(&mz->lru_lock, flags);
        unlock_page_cgroup(pc);

        res_counter_uncharge(&mem->res, PAGE_SIZE);
        css_put(&mem->css);

        return;

unlock_out:
        unlock_page_cgroup(pc);
        return;
}

void mem_cgroup_uncharge_page(struct page *page)
{
        /* early check. */
        if (page_mapped(page))
                return;
        if (page->mapping && !PageAnon(page))
                return;
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

void mem_cgroup_uncharge_cache_page(struct page *page)
{
        VM_BUG_ON(page_mapped(page));
        VM_BUG_ON(page->mapping);
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
}

void mem_cgroup_uncharge_swapcache(struct page *page)
{
        __mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_SWAPOUT);
}

/*
 * Before starting migration, account PAGE_SIZE to mem_cgroup that the old
 * page belongs to.
 */
int mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr)
{
        struct page_cgroup *pc;
        struct mem_cgroup *mem = NULL;
        int ret = 0;

        if (mem_cgroup_subsys.disabled)
                return 0;

        pc = lookup_page_cgroup(page);
        lock_page_cgroup(pc);
        if (PageCgroupUsed(pc)) {
                mem = pc->mem_cgroup;
                css_get(&mem->css);
        }
        unlock_page_cgroup(pc);

        if (mem) {
                ret = mem_cgroup_try_charge(NULL, GFP_HIGHUSER_MOVABLE, &mem);
                css_put(&mem->css);
        }
        *ptr = mem;
        return ret;
}

/* remove redundant charge if migration failed*/
void mem_cgroup_end_migration(struct mem_cgroup *mem,
                struct page *oldpage, struct page *newpage)
{
        struct page *target, *unused;
        struct page_cgroup *pc;
        enum charge_type ctype;

        if (!mem)
                return;

        /* at migration success, oldpage->mapping is NULL. */
        if (oldpage->mapping) {
                target = oldpage;
                unused = NULL;
        } else {
                target = newpage;
                unused = oldpage;
        }

        if (PageAnon(target))
                ctype = MEM_CGROUP_CHARGE_TYPE_MAPPED;
        else if (page_is_file_cache(target))
                ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
        else
                ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;

        /* unused page is not on radix-tree now. */
        if (unused)
                __mem_cgroup_uncharge_common(unused, ctype);

        pc = lookup_page_cgroup(target);
        /*
         * __mem_cgroup_commit_charge() check PCG_USED bit of page_cgroup.
         * So, double-counting is effectively avoided.
         */
        __mem_cgroup_commit_charge(mem, pc, ctype);

        /*
         * Both of oldpage and newpage are still under lock_page().
         * Then, we don't have to care about race in radix-tree.
         * But we have to be careful that this page is unmapped or not.
         *
         * There is a case for !page_mapped(). At the start of
         * migration, oldpage was mapped. But now, it's zapped.
         * But we know *target* page is not freed/reused under us.
         * mem_cgroup_uncharge_page() does all necessary checks.
         */
        if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
                mem_cgroup_uncharge_page(target);
}

/*
 * A call to try to shrink memory usage under specified resource controller.
 * This is typically used for page reclaiming for shmem for reducing side
 * effect of page allocation from shmem, which is used by some mem_cgroup.
 */
int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
{
        struct mem_cgroup *mem;
        int progress = 0;
        int retry = MEM_CGROUP_RECLAIM_RETRIES;

        if (mem_cgroup_subsys.disabled)
                return 0;
        if (!mm)
                return 0;

        rcu_read_lock();
        mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
        if (unlikely(!mem)) {
                rcu_read_unlock();
                return 0;
        }
        css_get(&mem->css);
        rcu_read_unlock();

        do {
                progress = try_to_free_mem_cgroup_pages(mem, gfp_mask);
                progress += res_counter_check_under_limit(&mem->res);
        } while (!progress && --retry);

        css_put(&mem->css);
        if (!retry)
                return -ENOMEM;
        return 0;
}

static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                                   unsigned long long val)
{

        int retry_count = MEM_CGROUP_RECLAIM_RETRIES;
        int progress;
        int ret = 0;

        while (res_counter_set_limit(&memcg->res, val)) {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
                if (!retry_count) {
                        ret = -EBUSY;
                        break;
                }
                progress = try_to_free_mem_cgroup_pages(memcg,
                                GFP_HIGHUSER_MOVABLE);
                if (!progress)
                        retry_count--;
        }
        return ret;
}


/*
 * This routine traverse page_cgroup in given list and drop them all.
 * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
 */
static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
                            struct mem_cgroup_per_zone *mz,
                            enum lru_list lru)
{
        struct page_cgroup *pc, *busy;
        unsigned long flags;
        unsigned long loop;
        struct list_head *list;
        int ret = 0;

        list = &mz->lists[lru];

        loop = MEM_CGROUP_ZSTAT(mz, lru);
        /* give some margin against EBUSY etc...*/
        loop += 256;
        busy = NULL;
        while (loop--) {
                ret = 0;
                spin_lock_irqsave(&mz->lru_lock, flags);
                if (list_empty(list)) {
                        spin_unlock_irqrestore(&mz->lru_lock, flags);
                        break;
                }
                pc = list_entry(list->prev, struct page_cgroup, lru);
                if (busy == pc) {
                        list_move(&pc->lru, list);
                        busy = 0;
                        spin_unlock_irqrestore(&mz->lru_lock, flags);
                        continue;
                }
                spin_unlock_irqrestore(&mz->lru_lock, flags);

                ret = mem_cgroup_move_parent(pc, mem, GFP_HIGHUSER_MOVABLE);
                if (ret == -ENOMEM)
                        break;

                if (ret == -EBUSY || ret == -EINVAL) {
                        /* found lock contention or "pc" is obsolete. */
                        busy = pc;
                        cond_resched();
                } else
                        busy = NULL;
        }
        if (!ret && !list_empty(list))
                return -EBUSY;
        return ret;
}

/*
 * make mem_cgroup's charge to be 0 if there is no task.
 * This enables deleting this mem_cgroup.
 */
static int mem_cgroup_force_empty(struct mem_cgroup *mem, bool free_all)
{
        int ret;
        int node, zid, shrink;
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct cgroup *cgrp = mem->css.cgroup;

        css_get(&mem->css);

        shrink = 0;
        /* should free all ? */
        if (free_all)
                goto try_to_free;
move_account:
        while (mem->res.usage > 0) {
                ret = -EBUSY;
                if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
                        goto out;
                ret = -EINTR;
                if (signal_pending(current))
                        goto out;
                /* This is for making all *used* pages to be on LRU. */
                lru_add_drain_all();
                ret = 0;
                for_each_node_state(node, N_POSSIBLE) {
                        for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
                                struct mem_cgroup_per_zone *mz;
                                enum lru_list l;
                                mz = mem_cgroup_zoneinfo(mem, node, zid);
                                for_each_lru(l) {
                                        ret = mem_cgroup_force_empty_list(mem,
                                                                  mz, l);
                                        if (ret)
                                                break;
                                }
                        }
                        if (ret)
                                break;
                }
                /* it seems parent cgroup doesn't have enough mem */
                if (ret == -ENOMEM)
                        goto try_to_free;
                cond_resched();
        }
        ret = 0;
out:
        css_put(&mem->css);
        return ret;

try_to_free:
        /* returns EBUSY if there is a task or if we come here twice. */
        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children) || shrink) {
                ret = -EBUSY;
                goto out;
        }
        /* we call try-to-free pages for make this cgroup empty */
        lru_add_drain_all();
        /* try to free all pages in this cgroup */
        shrink = 1;
        while (nr_retries && mem->res.usage > 0) {
                int progress;

                if (signal_pending(current)) {
                        ret = -EINTR;
                        goto out;
                }
                progress = try_to_free_mem_cgroup_pages(mem,
                                                  GFP_HIGHUSER_MOVABLE);
                if (!progress) {
                        nr_retries--;
                        /* maybe some writeback is necessary */
                        congestion_wait(WRITE, HZ/10);
                }

        }
        /* try move_account...there may be some *locked* pages. */
        if (mem->res.usage)
                goto move_account;
        ret = 0;
        goto out;
}

int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
{
        return mem_cgroup_force_empty(mem_cgroup_from_cont(cont), true);
}


static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
{
        return res_counter_read_u64(&mem_cgroup_from_cont(cont)->res,
                                    cft->private);
}
/*
 * The user of this function is...
 * RES_LIMIT.
 */
static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
                            const char *buffer)
{
        struct mem_cgroup *memcg = mem_cgroup_from_cont(cont);
        unsigned long long val;
        int ret;

        switch (cft->private) {
        case RES_LIMIT:
                /* This function does all necessary parse...reuse it */
                ret = res_counter_memparse_write_strategy(buffer, &val);
                if (!ret)
                        ret = mem_cgroup_resize_limit(memcg, val);
                break;
        default:
                ret = -EINVAL; /* should be BUG() ? */
                break;
        }
        return ret;
}

static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
{
        struct mem_cgroup *mem;

        mem = mem_cgroup_from_cont(cont);
        switch (event) {
        case RES_MAX_USAGE:
                res_counter_reset_max(&mem->res);
                break;
        case RES_FAILCNT:
                res_counter_reset_failcnt(&mem->res);
                break;
        }
        return 0;
}

static const struct mem_cgroup_stat_desc {
        const char *msg;
        u64 unit;
} mem_cgroup_stat_desc[] = {
        [MEM_CGROUP_STAT_CACHE] = { "cache", PAGE_SIZE, },
        [MEM_CGROUP_STAT_RSS] = { "rss", PAGE_SIZE, },
        [MEM_CGROUP_STAT_PGPGIN_COUNT] = {"pgpgin", 1, },
        [MEM_CGROUP_STAT_PGPGOUT_COUNT] = {"pgpgout", 1, },
};

static int mem_control_stat_show(struct cgroup *cont, struct cftype *cft,
                                 struct cgroup_map_cb *cb)
{
        struct mem_cgroup *mem_cont = mem_cgroup_from_cont(cont);
        struct mem_cgroup_stat *stat = &mem_cont->stat;
        int i;

        for (i = 0; i < ARRAY_SIZE(stat->cpustat[0].count); i++) {
                s64 val;

                val = mem_cgroup_read_stat(stat, i);
                val *= mem_cgroup_stat_desc[i].unit;
                cb->fill(cb, mem_cgroup_stat_desc[i].msg, val);
        }
        /* showing # of active pages */
        {
                unsigned long active_anon, inactive_anon;
                unsigned long active_file, inactive_file;
                unsigned long unevictable;

                inactive_anon = mem_cgroup_get_all_zonestat(mem_cont,
                                                LRU_INACTIVE_ANON);
                active_anon = mem_cgroup_get_all_zonestat(mem_cont,
                                                LRU_ACTIVE_ANON);
                inactive_file = mem_cgroup_get_all_zonestat(mem_cont,
                                                LRU_INACTIVE_FILE);
                active_file = mem_cgroup_get_all_zonestat(mem_cont,
                                                LRU_ACTIVE_FILE);
                unevictable = mem_cgroup_get_all_zonestat(mem_cont,
                                                        LRU_UNEVICTABLE);

                cb->fill(cb, "active_anon", (active_anon) * PAGE_SIZE);
                cb->fill(cb, "inactive_anon", (inactive_anon) * PAGE_SIZE);
                cb->fill(cb, "active_file", (active_file) * PAGE_SIZE);
                cb->fill(cb, "inactive_file", (inactive_file) * PAGE_SIZE);
                cb->fill(cb, "unevictable", unevictable * PAGE_SIZE);

        }
        return 0;
}


static struct cftype mem_cgroup_files[] = {
        {
                .name = "usage_in_bytes",
                .private = RES_USAGE,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "max_usage_in_bytes",
                .private = RES_MAX_USAGE,
                .trigger = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "limit_in_bytes",
                .private = RES_LIMIT,
                .write_string = mem_cgroup_write,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "failcnt",
                .private = RES_FAILCNT,
                .trigger = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read,
        },
        {
                .name = "stat",
                .read_map = mem_control_stat_show,
        },
        {
                .name = "force_empty",
                .trigger = mem_cgroup_force_empty_write,
        },
};

static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
{
        struct mem_cgroup_per_node *pn;
        struct mem_cgroup_per_zone *mz;
        enum lru_list l;
        int zone, tmp = node;
        /*
         * This routine is called against possible nodes.
         * But it's BUG to call kmalloc() against offline node.
         *
         * TODO: this routine can waste much memory for nodes which will
         *       never be onlined. It's better to use memory hotplug callback
         *       function.
         */
        if (!node_state(node, N_NORMAL_MEMORY))
                tmp = -1;
        pn = kmalloc_node(sizeof(*pn), GFP_KERNEL, tmp);
        if (!pn)
                return 1;

        mem->info.nodeinfo[node] = pn;
        memset(pn, 0, sizeof(*pn));

        for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                mz = &pn->zoneinfo[zone];
                spin_lock_init(&mz->lru_lock);
                for_each_lru(l)
                        INIT_LIST_HEAD(&mz->lists[l]);
        }
        return 0;
}

static void free_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
{
        kfree(mem->info.nodeinfo[node]);
}

static int mem_cgroup_size(void)
{
        int cpustat_size = nr_cpu_ids * sizeof(struct mem_cgroup_stat_cpu);
        return sizeof(struct mem_cgroup) + cpustat_size;
}

static struct mem_cgroup *mem_cgroup_alloc(void)
{
        struct mem_cgroup *mem;
        int size = mem_cgroup_size();

        if (size < PAGE_SIZE)
                mem = kmalloc(size, GFP_KERNEL);
        else
                mem = vmalloc(size);

        if (mem)
                memset(mem, 0, size);
        return mem;
}

static void mem_cgroup_free(struct mem_cgroup *mem)
{
        if (mem_cgroup_size() < PAGE_SIZE)
                kfree(mem);
        else
                vfree(mem);
}


static struct cgroup_subsys_state *
mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
{
        struct mem_cgroup *mem;
        int node;

        mem = mem_cgroup_alloc();
        if (!mem)
                return ERR_PTR(-ENOMEM);

        res_counter_init(&mem->res);

        for_each_node_state(node, N_POSSIBLE)
                if (alloc_mem_cgroup_per_zone_info(mem, node))
                        goto free_out;

        return &mem->css;
free_out:
        for_each_node_state(node, N_POSSIBLE)
                free_mem_cgroup_per_zone_info(mem, node);
        mem_cgroup_free(mem);
        return ERR_PTR(-ENOMEM);
}

static void mem_cgroup_pre_destroy(struct cgroup_subsys *ss,
                                        struct cgroup *cont)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
        mem_cgroup_force_empty(mem, false);
}

static void mem_cgroup_destroy(struct cgroup_subsys *ss,
                                struct cgroup *cont)
{
        int node;
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);

        for_each_node_state(node, N_POSSIBLE)
                free_mem_cgroup_per_zone_info(mem, node);

        mem_cgroup_free(mem_cgroup_from_cont(cont));
}

static int mem_cgroup_populate(struct cgroup_subsys *ss,
                                struct cgroup *cont)
{
        return cgroup_add_files(cont, ss, mem_cgroup_files,
                                        ARRAY_SIZE(mem_cgroup_files));
}

static void mem_cgroup_move_task(struct cgroup_subsys *ss,
                                struct cgroup *cont,
                                struct cgroup *old_cont,
                                struct task_struct *p)
{
        struct mm_struct *mm;
        struct mem_cgroup *mem, *old_mem;

        mm = get_task_mm(p);
        if (mm == NULL)
                return;

        mem = mem_cgroup_from_cont(cont);
        old_mem = mem_cgroup_from_cont(old_cont);

        /*
         * Only thread group leaders are allowed to migrate, the mm_struct is
         * in effect owned by the leader
         */
        if (!thread_group_leader(p))
                goto out;

out:
        mmput(mm);
}

struct cgroup_subsys mem_cgroup_subsys = {
        .name = "memory",
        .subsys_id = mem_cgroup_subsys_id,
        .create = mem_cgroup_create,
        .pre_destroy = mem_cgroup_pre_destroy,
        .destroy = mem_cgroup_destroy,
        .populate = mem_cgroup_populate,
        .attach = mem_cgroup_move_task,
        .early_init = 0,
};