memcg: avoid unnecessary initialization

[deliverable/linux.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/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 <asm/uaccess.h>

struct cgroup_subsys mem_cgroup_subsys __read_mostly;
static struct kmem_cache *page_cgroup_cache __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[NR_CPUS];
};

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

enum mem_cgroup_zstat_index {
        MEM_CGROUP_ZSTAT_ACTIVE,
        MEM_CGROUP_ZSTAT_INACTIVE,

        NR_MEM_CGROUP_ZSTAT,
};

struct mem_cgroup_per_zone {
        /*
         * spin_lock to protect the per cgroup LRU
         */
        spinlock_t              lru_lock;
        struct list_head        active_list;
        struct list_head        inactive_list;
        unsigned long count[NR_MEM_CGROUP_ZSTAT];
};
/* 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.
         */
        struct mem_cgroup_stat stat;
};
static struct mem_cgroup init_mem_cgroup;

/*
 * We use the lower bit of the page->page_cgroup pointer as a bit spin
 * lock.  We need to ensure that page->page_cgroup is at least two
 * byte aligned (based on comments from Nick Piggin).  But since
 * bit_spin_lock doesn't actually set that lock bit in a non-debug
 * uniprocessor kernel, we should avoid setting it here too.
 */
#define PAGE_CGROUP_LOCK_BIT    0x0
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
#define PAGE_CGROUP_LOCK        (1 << PAGE_CGROUP_LOCK_BIT)
#else
#define PAGE_CGROUP_LOCK        0x0
#endif

/*
 * A page_cgroup page is associated with every page descriptor. The
 * page_cgroup helps us identify information about the cgroup
 */
struct page_cgroup {
        struct list_head lru;           /* per cgroup LRU list */
        struct page *page;
        struct mem_cgroup *mem_cgroup;
        int ref_cnt;                    /* cached, mapped, migrating */
        int flags;
};
#define PAGE_CGROUP_FLAG_CACHE  (0x1)   /* charged as cache */
#define PAGE_CGROUP_FLAG_ACTIVE (0x2)   /* page is active in this cgroup */

static int page_cgroup_nid(struct page_cgroup *pc)
{
        return page_to_nid(pc->page);
}

static enum zone_type page_cgroup_zid(struct page_cgroup *pc)
{
        return page_zonenum(pc->page);
}

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_MAPPED,
};

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

        VM_BUG_ON(!irqs_disabled());
        if (flags & PAGE_CGROUP_FLAG_CACHE)
                __mem_cgroup_stat_add_safe(stat, MEM_CGROUP_STAT_CACHE, val);
        else
                __mem_cgroup_stat_add_safe(stat, MEM_CGROUP_STAT_RSS, val);

        if (charge)
                __mem_cgroup_stat_add_safe(stat,
                                MEM_CGROUP_STAT_PGPGIN_COUNT, 1);
        else
                __mem_cgroup_stat_add_safe(stat,
                                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 mem_cgroup_zstat_index 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)
{
        return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
                                struct mem_cgroup, css);
}

static inline int page_cgroup_locked(struct page *page)
{
        return bit_spin_is_locked(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}

static void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
{
        VM_BUG_ON(!page_cgroup_locked(page));
        page->page_cgroup = ((unsigned long)pc | PAGE_CGROUP_LOCK);
}

struct page_cgroup *page_get_page_cgroup(struct page *page)
{
        return (struct page_cgroup *) (page->page_cgroup & ~PAGE_CGROUP_LOCK);
}

static void lock_page_cgroup(struct page *page)
{
        bit_spin_lock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}

static int try_lock_page_cgroup(struct page *page)
{
        return bit_spin_trylock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}

static void unlock_page_cgroup(struct page *page)
{
        bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
}

static void __mem_cgroup_remove_list(struct mem_cgroup_per_zone *mz,
                        struct page_cgroup *pc)
{
        int from = pc->flags & PAGE_CGROUP_FLAG_ACTIVE;

        if (from)
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_ACTIVE) -= 1;
        else
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE) -= 1;

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

static void __mem_cgroup_add_list(struct mem_cgroup_per_zone *mz,
                                struct page_cgroup *pc)
{
        int to = pc->flags & PAGE_CGROUP_FLAG_ACTIVE;

        if (!to) {
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE) += 1;
                list_add(&pc->lru, &mz->inactive_list);
        } else {
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_ACTIVE) += 1;
                list_add(&pc->lru, &mz->active_list);
        }
        mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, true);
}

static void __mem_cgroup_move_lists(struct page_cgroup *pc, bool active)
{
        int from = pc->flags & PAGE_CGROUP_FLAG_ACTIVE;
        struct mem_cgroup_per_zone *mz = page_cgroup_zoneinfo(pc);

        if (from)
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_ACTIVE) -= 1;
        else
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE) -= 1;

        if (active) {
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_ACTIVE) += 1;
                pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
                list_move(&pc->lru, &mz->active_list);
        } else {
                MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE) += 1;
                pc->flags &= ~PAGE_CGROUP_FLAG_ACTIVE;
                list_move(&pc->lru, &mz->inactive_list);
        }
}

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, bool active)
{
        struct page_cgroup *pc;
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;

        /*
         * 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.
         */
        if (!try_lock_page_cgroup(page))
                return;

        pc = page_get_page_cgroup(page);
        if (pc) {
                mz = page_cgroup_zoneinfo(pc);
                spin_lock_irqsave(&mz->lru_lock, flags);
                __mem_cgroup_move_lists(pc, active);
                spin_unlock_irqrestore(&mz->lru_lock, flags);
        }
        unlock_page_cgroup(page);
}

/*
 * 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);
}

/*
 * This function is called from vmscan.c. In page reclaiming loop. balance
 * between active and inactive list is calculated. For memory controller
 * page reclaiming, we should use using mem_cgroup's imbalance rather than
 * zone's global lru imbalance.
 */
long mem_cgroup_reclaim_imbalance(struct mem_cgroup *mem)
{
        unsigned long active, inactive;
        /* active and inactive are the number of pages. 'long' is ok.*/
        active = mem_cgroup_get_all_zonestat(mem, MEM_CGROUP_ZSTAT_ACTIVE);
        inactive = mem_cgroup_get_all_zonestat(mem, MEM_CGROUP_ZSTAT_INACTIVE);
        return (long) (active / (inactive + 1));
}

/*
 * 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_active(struct mem_cgroup *mem,
                                   struct zone *zone, int priority)
{
        long nr_active;
        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_active = MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_ACTIVE);
        return (nr_active >> priority);
}

long mem_cgroup_calc_reclaim_inactive(struct mem_cgroup *mem,
                                        struct zone *zone, int priority)
{
        long nr_inactive;
        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_inactive = MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE);
        return (nr_inactive >> 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)
{
        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;

        BUG_ON(!mem_cont);
        mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);
        if (active)
                src = &mz->active_list;
        else
                src = &mz->inactive_list;


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

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

                if (PageActive(page) && !active) {
                        __mem_cgroup_move_lists(pc, true);
                        continue;
                }
                if (!PageActive(page) && active) {
                        __mem_cgroup_move_lists(pc, false);
                        continue;
                }

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

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

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

        *scanned = scan;
        return nr_taken;
}

/*
 * 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 *mem;
        struct page_cgroup *pc;
        unsigned long flags;
        unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct mem_cgroup_per_zone *mz;

        if (mem_cgroup_subsys.disabled)
                return 0;

        /*
         * Should page_cgroup's go to their own slab?
         * One could optimize the performance of the charging routine
         * by saving a bit in the page_flags and using it as a lock
         * to see if the cgroup page already has a page_cgroup associated
         * with it
         */
retry:
        lock_page_cgroup(page);
        pc = page_get_page_cgroup(page);
        /*
         * The page_cgroup exists and
         * the page has already been accounted.
         */
        if (pc) {
                VM_BUG_ON(pc->page != page);
                VM_BUG_ON(pc->ref_cnt <= 0);

                pc->ref_cnt++;
                unlock_page_cgroup(page);
                goto done;
        }
        unlock_page_cgroup(page);

        pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
        if (pc == NULL)
                goto err;

        /*
         * 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 (!mm)
                mm = &init_mm;

        rcu_read_lock();
        mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
        /*
         * For every charge from the cgroup, increment reference count
         */
        css_get(&mem->css);
        rcu_read_unlock();

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

                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--) {
                        mem_cgroup_out_of_memory(mem, gfp_mask);
                        goto out;
                }
        }

        pc->ref_cnt = 1;
        pc->mem_cgroup = mem;
        pc->page = page;
        /*
         * If a page is accounted as a page cache, insert to inactive list.
         * If anon, insert to active list.
         */
        if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
                pc->flags = PAGE_CGROUP_FLAG_CACHE;
        else
                pc->flags = PAGE_CGROUP_FLAG_ACTIVE;

        lock_page_cgroup(page);
        if (page_get_page_cgroup(page)) {
                unlock_page_cgroup(page);
                /*
                 * Another charge has been added to this page already.
                 * We take lock_page_cgroup(page) again and read
                 * page->cgroup, increment refcnt.... just retry is OK.
                 */
                res_counter_uncharge(&mem->res, PAGE_SIZE);
                css_put(&mem->css);
                kmem_cache_free(page_cgroup_cache, pc);
                goto retry;
        }
        page_assign_page_cgroup(page, pc);

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

        unlock_page_cgroup(page);
done:
        return 0;
out:
        css_put(&mem->css);
        kmem_cache_free(page_cgroup_cache, pc);
err:
        return -ENOMEM;
}

int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
{
        return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_MAPPED);
}

int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
{
        if (!mm)
                mm = &init_mm;
        return mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_CACHE);
}

/*
 * Uncharging is always a welcome operation, we never complain, simply
 * uncharge.
 */
void mem_cgroup_uncharge_page(struct page *page)
{
        struct page_cgroup *pc;
        struct mem_cgroup *mem;
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;

        if (mem_cgroup_subsys.disabled)
                return;

        /*
         * Check if our page_cgroup is valid
         */
        lock_page_cgroup(page);
        pc = page_get_page_cgroup(page);
        if (!pc)
                goto unlock;

        VM_BUG_ON(pc->page != page);
        VM_BUG_ON(pc->ref_cnt <= 0);

        if (--(pc->ref_cnt) == 0) {
                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);

                page_assign_page_cgroup(page, NULL);
                unlock_page_cgroup(page);

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

                kmem_cache_free(page_cgroup_cache, pc);
                return;
        }

unlock:
        unlock_page_cgroup(page);
}

/*
 * Returns non-zero if a page (under migration) has valid page_cgroup member.
 * Refcnt of page_cgroup is incremented.
 */
int mem_cgroup_prepare_migration(struct page *page)
{
        struct page_cgroup *pc;

        if (mem_cgroup_subsys.disabled)
                return 0;

        lock_page_cgroup(page);
        pc = page_get_page_cgroup(page);
        if (pc)
                pc->ref_cnt++;
        unlock_page_cgroup(page);
        return pc != NULL;
}

void mem_cgroup_end_migration(struct page *page)
{
        mem_cgroup_uncharge_page(page);
}

/*
 * We know both *page* and *newpage* are now not-on-LRU and PG_locked.
 * And no race with uncharge() routines because page_cgroup for *page*
 * has extra one reference by mem_cgroup_prepare_migration.
 */
void mem_cgroup_page_migration(struct page *page, struct page *newpage)
{
        struct page_cgroup *pc;
        struct mem_cgroup_per_zone *mz;
        unsigned long flags;

        lock_page_cgroup(page);
        pc = page_get_page_cgroup(page);
        if (!pc) {
                unlock_page_cgroup(page);
                return;
        }

        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);

        page_assign_page_cgroup(page, NULL);
        unlock_page_cgroup(page);

        pc->page = newpage;
        lock_page_cgroup(newpage);
        page_assign_page_cgroup(newpage, pc);

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

        unlock_page_cgroup(newpage);
}

/*
 * This routine traverse page_cgroup in given list and drop them all.
 * This routine ignores page_cgroup->ref_cnt.
 * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
 */
#define FORCE_UNCHARGE_BATCH    (128)
static void mem_cgroup_force_empty_list(struct mem_cgroup *mem,
                            struct mem_cgroup_per_zone *mz,
                            int active)
{
        struct page_cgroup *pc;
        struct page *page;
        int count = FORCE_UNCHARGE_BATCH;
        unsigned long flags;
        struct list_head *list;

        if (active)
                list = &mz->active_list;
        else
                list = &mz->inactive_list;

        spin_lock_irqsave(&mz->lru_lock, flags);
        while (!list_empty(list)) {
                pc = list_entry(list->prev, struct page_cgroup, lru);
                page = pc->page;
                get_page(page);
                spin_unlock_irqrestore(&mz->lru_lock, flags);
                mem_cgroup_uncharge_page(page);
                put_page(page);
                if (--count <= 0) {
                        count = FORCE_UNCHARGE_BATCH;
                        cond_resched();
                }
                spin_lock_irqsave(&mz->lru_lock, flags);
        }
        spin_unlock_irqrestore(&mz->lru_lock, flags);
}

/*
 * 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)
{
        int ret = -EBUSY;
        int node, zid;

        if (mem_cgroup_subsys.disabled)
                return 0;

        css_get(&mem->css);
        /*
         * page reclaim code (kswapd etc..) will move pages between
         * active_list <-> inactive_list while we don't take a lock.
         * So, we have to do loop here until all lists are empty.
         */
        while (mem->res.usage > 0) {
                if (atomic_read(&mem->css.cgroup->count) > 0)
                        goto out;
                for_each_node_state(node, N_POSSIBLE)
                        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                                struct mem_cgroup_per_zone *mz;
                                mz = mem_cgroup_zoneinfo(mem, node, zid);
                                /* drop all page_cgroup in active_list */
                                mem_cgroup_force_empty_list(mem, mz, 1);
                                /* drop all page_cgroup in inactive_list */
                                mem_cgroup_force_empty_list(mem, mz, 0);
                        }
        }
        ret = 0;
out:
        css_put(&mem->css);
        return ret;
}

static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
{
        return res_counter_read_u64(&mem_cgroup_from_cont(cont)->res,
                                    cft->private);
}

static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
                            const char *buffer)
{
        return res_counter_write(&mem_cgroup_from_cont(cont)->res,
                                 cft->private, buffer,
                                 res_counter_memparse_write_strategy);
}

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

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, inactive;

                inactive = mem_cgroup_get_all_zonestat(mem_cont,
                                                MEM_CGROUP_ZSTAT_INACTIVE);
                active = mem_cgroup_get_all_zonestat(mem_cont,
                                                MEM_CGROUP_ZSTAT_ACTIVE);
                cb->fill(cb, "active", (active) * PAGE_SIZE);
                cb->fill(cb, "inactive", (inactive) * 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 = "force_empty",
                .trigger = mem_force_empty_write,
        },
        {
                .name = "stat",
                .read_map = mem_control_stat_show,
        },
};

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;
        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];
                INIT_LIST_HEAD(&mz->active_list);
                INIT_LIST_HEAD(&mz->inactive_list);
                spin_lock_init(&mz->lru_lock);
        }
        return 0;
}

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

static struct mem_cgroup *mem_cgroup_alloc(void)
{
        struct mem_cgroup *mem;

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

        if (mem)
                memset(mem, 0, sizeof(*mem));
        return mem;
}

static void mem_cgroup_free(struct mem_cgroup *mem)
{
        if (sizeof(*mem) < 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;

        if (unlikely((cont->parent) == NULL)) {
                mem = &init_mem_cgroup;
                page_cgroup_cache = KMEM_CACHE(page_cgroup, SLAB_PANIC);
        } else {
                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);
        if (cont->parent != NULL)
                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);
}

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)
{
        if (mem_cgroup_subsys.disabled)
                return 0;
        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;

        if (mem_cgroup_subsys.disabled)
                return;

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

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

        if (mem == old_mem)
                goto out;

        /*
         * 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,
};