memory cgroup enhancements: remember "a page is on active list of cgroup or not"

[linux-2.6/verdex.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/page-flags.h>
#include <linux/backing-dev.h>
#include <linux/bit_spinlock.h>
#include <linux/rcupdate.h>
#include <linux/swap.h>
#include <linux/spinlock.h>
#include <linux/fs.h>

#include <asm/uaccess.h>

struct cgroup_subsys mem_cgroup_subsys;
static const int MEM_CGROUP_RECLAIM_RETRIES = 5;

/*
 * 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.
         * TODO: Consider making these lists per zone
         */
        struct list_head active_list;
        struct list_head inactive_list;
        /*
         * spin_lock to protect the per cgroup LRU
         */
        spinlock_t lru_lock;
        unsigned long control_type;     /* control RSS or RSS+Pagecache */
};

/*
 * 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 atleast two
 * byte aligned (based on comments from Nick Piggin)
 */
#define PAGE_CGROUP_LOCK_BIT    0x0
#define PAGE_CGROUP_LOCK                (1 << PAGE_CGROUP_LOCK_BIT)

/*
 * 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;
        atomic_t ref_cnt;               /* Helpful when pages move b/w  */
                                        /* mapped and cached states     */
        int      flags;
};
#define PAGE_CGROUP_FLAG_CACHE  (0x1)   /* charged as cache */
#define PAGE_CGROUP_FLAG_ACTIVE (0x2)   /* page is active in this cgroup */

enum {
        MEM_CGROUP_TYPE_UNSPEC = 0,
        MEM_CGROUP_TYPE_MAPPED,
        MEM_CGROUP_TYPE_CACHED,
        MEM_CGROUP_TYPE_ALL,
        MEM_CGROUP_TYPE_MAX,
};

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_MAPPED,
};

static struct mem_cgroup init_mem_cgroup;

static inline
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);
}

static inline
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);
}

void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p)
{
        struct mem_cgroup *mem;

        mem = mem_cgroup_from_task(p);
        css_get(&mem->css);
        mm->mem_cgroup = mem;
}

void mm_free_cgroup(struct mm_struct *mm)
{
        css_put(&mm->mem_cgroup->css);
}

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

void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
{
        int locked;

        /*
         * While resetting the page_cgroup we might not hold the
         * page_cgroup lock. free_hot_cold_page() is an example
         * of such a scenario
         */
        if (pc)
                VM_BUG_ON(!page_cgroup_locked(page));
        locked = (page->page_cgroup & PAGE_CGROUP_LOCK);
        page->page_cgroup = ((unsigned long)pc | locked);
}

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

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

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

/*
 * Tie new page_cgroup to struct page under lock_page_cgroup()
 * This can fail if the page has been tied to a page_cgroup.
 * If success, returns 0.
 */
static inline int
page_cgroup_assign_new_page_cgroup(struct page *page, struct page_cgroup *pc)
{
        int ret = 0;

        lock_page_cgroup(page);
        if (!page_get_page_cgroup(page))
                page_assign_page_cgroup(page, pc);
        else /* A page is tied to other pc. */
                ret = 1;
        unlock_page_cgroup(page);
        return ret;
}

/*
 * Clear page->page_cgroup member under lock_page_cgroup().
 * If given "pc" value is different from one page->page_cgroup,
 * page->cgroup is not cleared.
 * Returns a value of page->page_cgroup at lock taken.
 * A can can detect failure of clearing by following
 *  clear_page_cgroup(page, pc) == pc
 */

static inline struct page_cgroup *
clear_page_cgroup(struct page *page, struct page_cgroup *pc)
{
        struct page_cgroup *ret;
        /* lock and clear */
        lock_page_cgroup(page);
        ret = page_get_page_cgroup(page);
        if (likely(ret == pc))
                page_assign_page_cgroup(page, NULL);
        unlock_page_cgroup(page);
        return ret;
}


static void __mem_cgroup_move_lists(struct page_cgroup *pc, bool active)
{
        if (active) {
                pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
                list_move(&pc->lru, &pc->mem_cgroup->active_list);
        } else {
                pc->flags &= ~PAGE_CGROUP_FLAG_ACTIVE;
                list_move(&pc->lru, &pc->mem_cgroup->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_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_cgroup *pc, bool active)
{
        struct mem_cgroup *mem;
        if (!pc)
                return;

        mem = pc->mem_cgroup;

        spin_lock(&mem->lru_lock);
        __mem_cgroup_move_lists(pc, active);
        spin_unlock(&mem->lru_lock);
}

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;

        if (active)
                src = &mem_cont->active_list;
        else
                src = &mem_cont->inactive_list;

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

                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;
                }

                /*
                 * Reclaim, per zone
                 * TODO: make the active/inactive lists per zone
                 */
                if (page_zone(page) != z)
                        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(&mem_cont->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;

        /*
         * 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:
        if (page) {
                lock_page_cgroup(page);
                pc = page_get_page_cgroup(page);
                /*
                 * The page_cgroup exists and
                 * the page has already been accounted.
                 */
                if (pc) {
                        if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) {
                                /* this page is under being uncharged ? */
                                unlock_page_cgroup(page);
                                cpu_relax();
                                goto retry;
                        } else {
                                unlock_page_cgroup(page);
                                goto done;
                        }
                }
                unlock_page_cgroup(page);
        }

        pc = kzalloc(sizeof(struct page_cgroup), 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 = rcu_dereference(mm->mem_cgroup);
        /*
         * For every charge from the cgroup, increment reference
         * count
         */
        css_get(&mem->css);
        rcu_read_unlock();

        /*
         * If we created the page_cgroup, we should free it on exceeding
         * the cgroup limit.
         */
        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;
                }
                congestion_wait(WRITE, HZ/10);
        }

        atomic_set(&pc->ref_cnt, 1);
        pc->mem_cgroup = mem;
        pc->page = page;
        pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
        if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
                pc->flags |= PAGE_CGROUP_FLAG_CACHE;

        if (!page || page_cgroup_assign_new_page_cgroup(page, pc)) {
                /*
                 * 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);
                kfree(pc);
                if (!page)
                        goto done;
                goto retry;
        }

        spin_lock_irqsave(&mem->lru_lock, flags);
        list_add(&pc->lru, &mem->active_list);
        spin_unlock_irqrestore(&mem->lru_lock, flags);

done:
        return 0;
out:
        css_put(&mem->css);
        kfree(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);
}

/*
 * See if the cached pages should be charged at all?
 */
int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
                                gfp_t gfp_mask)
{
        int ret = 0;
        struct mem_cgroup *mem;
        if (!mm)
                mm = &init_mm;

        rcu_read_lock();
        mem = rcu_dereference(mm->mem_cgroup);
        css_get(&mem->css);
        rcu_read_unlock();
        if (mem->control_type == MEM_CGROUP_TYPE_ALL)
                ret = mem_cgroup_charge_common(page, mm, gfp_mask,
                                MEM_CGROUP_CHARGE_TYPE_CACHE);
        css_put(&mem->css);
        return ret;
}

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

        /*
         * This can handle cases when a page is not charged at all and we
         * are switching between handling the control_type.
         */
        if (!pc)
                return;

        if (atomic_dec_and_test(&pc->ref_cnt)) {
                page = pc->page;
                /*
                 * get page->cgroup and clear it under lock.
                 * force_empty can drop page->cgroup without checking refcnt.
                 */
                if (clear_page_cgroup(page, pc) == pc) {
                        mem = pc->mem_cgroup;
                        css_put(&mem->css);
                        res_counter_uncharge(&mem->res, PAGE_SIZE);
                        spin_lock_irqsave(&mem->lru_lock, flags);
                        list_del_init(&pc->lru);
                        spin_unlock_irqrestore(&mem->lru_lock, flags);
                        kfree(pc);
                }
        }
}
/*
 * 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;
        int ret = 0;
        lock_page_cgroup(page);
        pc = page_get_page_cgroup(page);
        if (pc && atomic_inc_not_zero(&pc->ref_cnt))
                ret = 1;
        unlock_page_cgroup(page);
        return ret;
}

void mem_cgroup_end_migration(struct page *page)
{
        struct page_cgroup *pc = page_get_page_cgroup(page);
        mem_cgroup_uncharge(pc);
}
/*
 * 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;
retry:
        pc = page_get_page_cgroup(page);
        if (!pc)
                return;
        if (clear_page_cgroup(page, pc) != pc)
                goto retry;
        pc->page = newpage;
        lock_page_cgroup(newpage);
        page_assign_page_cgroup(newpage, pc);
        unlock_page_cgroup(newpage);
        return;
}

/*
 * 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 list_head *list)
{
        struct page_cgroup *pc;
        struct page *page;
        int count;
        unsigned long flags;

retry:
        count = FORCE_UNCHARGE_BATCH;
        spin_lock_irqsave(&mem->lru_lock, flags);

        while (--count && !list_empty(list)) {
                pc = list_entry(list->prev, struct page_cgroup, lru);
                page = pc->page;
                /* Avoid race with charge */
                atomic_set(&pc->ref_cnt, 0);
                if (clear_page_cgroup(page, pc) == pc) {
                        css_put(&mem->css);
                        res_counter_uncharge(&mem->res, PAGE_SIZE);
                        list_del_init(&pc->lru);
                        kfree(pc);
                } else  /* being uncharged ? ...do relax */
                        break;
        }
        spin_unlock_irqrestore(&mem->lru_lock, flags);
        if (!list_empty(list)) {
                cond_resched();
                goto retry;
        }
        return;
}

/*
 * make mem_cgroup's charge to be 0 if there is no task.
 * This enables deleting this mem_cgroup.
 */

int mem_cgroup_force_empty(struct mem_cgroup *mem)
{
        int ret = -EBUSY;
        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 (!(list_empty(&mem->active_list) &&
                 list_empty(&mem->inactive_list))) {
                if (atomic_read(&mem->css.cgroup->count) > 0)
                        goto out;
                /* drop all page_cgroup in active_list */
                mem_cgroup_force_empty_list(mem, &mem->active_list);
                /* drop all page_cgroup in inactive_list */
                mem_cgroup_force_empty_list(mem, &mem->inactive_list);
        }
        ret = 0;
out:
        css_put(&mem->css);
        return ret;
}



int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
{
        *tmp = memparse(buf, &buf);
        if (*buf != '\0')
                return -EINVAL;

        /*
         * Round up the value to the closest page size
         */
        *tmp = ((*tmp + PAGE_SIZE - 1) >> PAGE_SHIFT) << PAGE_SHIFT;
        return 0;
}

static ssize_t mem_cgroup_read(struct cgroup *cont,
                        struct cftype *cft, struct file *file,
                        char __user *userbuf, size_t nbytes, loff_t *ppos)
{
        return res_counter_read(&mem_cgroup_from_cont(cont)->res,
                                cft->private, userbuf, nbytes, ppos,
                                NULL);
}

static ssize_t mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
                                struct file *file, const char __user *userbuf,
                                size_t nbytes, loff_t *ppos)
{
        return res_counter_write(&mem_cgroup_from_cont(cont)->res,
                                cft->private, userbuf, nbytes, ppos,
                                mem_cgroup_write_strategy);
}

static ssize_t mem_control_type_write(struct cgroup *cont,
                        struct cftype *cft, struct file *file,
                        const char __user *userbuf,
                        size_t nbytes, loff_t *pos)
{
        int ret;
        char *buf, *end;
        unsigned long tmp;
        struct mem_cgroup *mem;

        mem = mem_cgroup_from_cont(cont);
        buf = kmalloc(nbytes + 1, GFP_KERNEL);
        ret = -ENOMEM;
        if (buf == NULL)
                goto out;

        buf[nbytes] = 0;
        ret = -EFAULT;
        if (copy_from_user(buf, userbuf, nbytes))
                goto out_free;

        ret = -EINVAL;
        tmp = simple_strtoul(buf, &end, 10);
        if (*end != '\0')
                goto out_free;

        if (tmp <= MEM_CGROUP_TYPE_UNSPEC || tmp >= MEM_CGROUP_TYPE_MAX)
                goto out_free;

        mem->control_type = tmp;
        ret = nbytes;
out_free:
        kfree(buf);
out:
        return ret;
}

static ssize_t mem_control_type_read(struct cgroup *cont,
                                struct cftype *cft,
                                struct file *file, char __user *userbuf,
                                size_t nbytes, loff_t *ppos)
{
        unsigned long val;
        char buf[64], *s;
        struct mem_cgroup *mem;

        mem = mem_cgroup_from_cont(cont);
        s = buf;
        val = mem->control_type;
        s += sprintf(s, "%lu\n", val);
        return simple_read_from_buffer((void __user *)userbuf, nbytes,
                        ppos, buf, s - buf);
}


static ssize_t mem_force_empty_write(struct cgroup *cont,
                                struct cftype *cft, struct file *file,
                                const char __user *userbuf,
                                size_t nbytes, loff_t *ppos)
{
        struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
        int ret;
        ret = mem_cgroup_force_empty(mem);
        if (!ret)
                ret = nbytes;
        return ret;
}

/*
 * Note: This should be removed if cgroup supports write-only file.
 */

static ssize_t mem_force_empty_read(struct cgroup *cont,
                                struct cftype *cft,
                                struct file *file, char __user *userbuf,
                                size_t nbytes, loff_t *ppos)
{
        return -EINVAL;
}


static struct cftype mem_cgroup_files[] = {
        {
                .name = "usage_in_bytes",
                .private = RES_USAGE,
                .read = mem_cgroup_read,
        },
        {
                .name = "limit_in_bytes",
                .private = RES_LIMIT,
                .write = mem_cgroup_write,
                .read = mem_cgroup_read,
        },
        {
                .name = "failcnt",
                .private = RES_FAILCNT,
                .read = mem_cgroup_read,
        },
        {
                .name = "control_type",
                .write = mem_control_type_write,
                .read = mem_control_type_read,
        },
        {
                .name = "force_empty",
                .write = mem_force_empty_write,
                .read = mem_force_empty_read,
        },
};

static struct mem_cgroup init_mem_cgroup;

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

        if (unlikely((cont->parent) == NULL)) {
                mem = &init_mem_cgroup;
                init_mm.mem_cgroup = mem;
        } else
                mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);

        if (mem == NULL)
                return NULL;

        res_counter_init(&mem->res);
        INIT_LIST_HEAD(&mem->active_list);
        INIT_LIST_HEAD(&mem->inactive_list);
        spin_lock_init(&mem->lru_lock);
        mem->control_type = MEM_CGROUP_TYPE_ALL;
        return &mem->css;
}

static void mem_cgroup_destroy(struct cgroup_subsys *ss,
                                struct cgroup *cont)
{
        kfree(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);

        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 (p->tgid != p->pid)
                goto out;

        css_get(&mem->css);
        rcu_assign_pointer(mm->mem_cgroup, mem);
        css_put(&old_mem->css);

out:
        mmput(mm);
        return;
}

struct cgroup_subsys mem_cgroup_subsys = {
        .name = "memory",
        .subsys_id = mem_cgroup_subsys_id,
        .create = mem_cgroup_create,
        .destroy = mem_cgroup_destroy,
        .populate = mem_cgroup_populate,
        .attach = mem_cgroup_move_task,
        .early_init = 1,
};