/* 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>
   *

   * Memory thresholds
   * Copyright (C) 2009 Nokia Corporation
   * Author: Kirill A. Shutemov
   *

   * 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/hugetlb.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/limits.h>

  #include <linux/mutex.h>

  #include <linux/rbtree.h>

  #include <linux/slab.h>

  #include <linux/swap.h>

  #include <linux/swapops.h>

  #include <linux/spinlock.h>

  #include <linux/eventfd.h>
  #include <linux/sort.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 <linux/cpu.h>

  #include <linux/oom.h>

  #include "internal.h"

  #include <asm/uaccess.h>

  #include <trace/events/vmscan.h>

  struct cgroup_subsys mem_cgroup_subsys __read_mostly;

  #define MEM_CGROUP_RECLAIM_RETRIES	5

  struct mem_cgroup *root_mem_cgroup __read_mostly;

  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP

  /* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */

  int do_swap_account __read_mostly;

  
  /* for remember boot option*/
  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED
  static int really_do_swap_account __initdata = 1;
  #else
  static int really_do_swap_account __initdata = 0;
  #endif

  #else
  #define do_swap_account		(0)
  #endif

  /*
   * Per memcg event counter is incremented at every pagein/pageout. This counter
   * is used for trigger some periodic events. This is straightforward and better
   * than using jiffies etc. to handle periodic memcg event.
   *
   * These values will be used as !((event) & ((1 <<(thresh)) - 1))
   */
  #define THRESHOLDS_EVENTS_THRESH (7) /* once in 128 */
  #define SOFTLIMIT_EVENTS_THRESH (10) /* once in 1024 */

  /*

   * 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 anon rss */

  	MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */

  	MEM_CGROUP_STAT_PGPGIN_COUNT,	/* # of pages paged in */
  	MEM_CGROUP_STAT_PGPGOUT_COUNT,	/* # of pages paged out */

  	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */

  	MEM_CGROUP_STAT_DATA, /* end of data requires synchronization */
  	/* incremented at every  pagein/pageout */
  	MEM_CGROUP_EVENTS = MEM_CGROUP_STAT_DATA,

  	MEM_CGROUP_ON_MOVE,	/* someone is moving account between groups */

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

  };

  /*

   * per-zone information in memory controller.
   */

  struct mem_cgroup_per_zone {

  	/*
  	 * spin_lock to protect the per cgroup LRU
  	 */

  	struct list_head	lists[NR_LRU_LISTS];
  	unsigned long		count[NR_LRU_LISTS];

  
  	struct zone_reclaim_stat reclaim_stat;

  	struct rb_node		tree_node;	/* RB tree node */
  	unsigned long long	usage_in_excess;/* Set to the value by which */
  						/* the soft limit is exceeded*/
  	bool			on_tree;

  	struct mem_cgroup	*mem;		/* Back pointer, we cannot */
  						/* use container_of	   */

  };
  /* 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];
  };
  
  /*

   * Cgroups above their limits are maintained in a RB-Tree, independent of
   * their hierarchy representation
   */
  
  struct mem_cgroup_tree_per_zone {
  	struct rb_root rb_root;
  	spinlock_t lock;
  };
  
  struct mem_cgroup_tree_per_node {
  	struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
  };
  
  struct mem_cgroup_tree {
  	struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
  };
  
  static struct mem_cgroup_tree soft_limit_tree __read_mostly;

  struct mem_cgroup_threshold {
  	struct eventfd_ctx *eventfd;
  	u64 threshold;
  };

  /* For threshold */

  struct mem_cgroup_threshold_ary {
  	/* An array index points to threshold just below usage. */

  	int current_threshold;

  	/* Size of entries[] */
  	unsigned int size;
  	/* Array of thresholds */
  	struct mem_cgroup_threshold entries[0];
  };

  
  struct mem_cgroup_thresholds {
  	/* Primary thresholds array */
  	struct mem_cgroup_threshold_ary *primary;
  	/*
  	 * Spare threshold array.
  	 * This is needed to make mem_cgroup_unregister_event() "never fail".
  	 * It must be able to store at least primary->size - 1 entries.
  	 */
  	struct mem_cgroup_threshold_ary *spare;
  };

  /* for OOM */
  struct mem_cgroup_eventfd_list {
  	struct list_head list;
  	struct eventfd_ctx *eventfd;
  };

  static void mem_cgroup_threshold(struct mem_cgroup *mem);

  static void mem_cgroup_oom_notify(struct mem_cgroup *mem);

  /*

   * 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;

  	/*

  	 * the counter to account for mem+swap usage.
  	 */
  	struct res_counter memsw;
  	/*

  	 * Per cgroup active and inactive list, similar to the
  	 * per zone LRU lists.

  	 */

  	struct mem_cgroup_lru_info info;

  	/*
  	  protect against reclaim related member.
  	*/
  	spinlock_t reclaim_param_lock;

  	/*

  	 * While reclaiming in a hierarchy, we cache the last child we

  	 * reclaimed from.

  	 */

  	int last_scanned_child;

  	/*
  	 * Should the accounting and control be hierarchical, per subtree?
  	 */
  	bool use_hierarchy;

  	atomic_t	oom_lock;

  	atomic_t	refcnt;

  	unsigned int	swappiness;

  	/* OOM-Killer disable */
  	int		oom_kill_disable;

  	/* set when res.limit == memsw.limit */
  	bool		memsw_is_minimum;

  	/* protect arrays of thresholds */
  	struct mutex thresholds_lock;
  
  	/* thresholds for memory usage. RCU-protected */

  	struct mem_cgroup_thresholds thresholds;

  	/* thresholds for mem+swap usage. RCU-protected */

  	struct mem_cgroup_thresholds memsw_thresholds;

  	/* For oom notifier event fd */
  	struct list_head oom_notify;

  	/*

  	 * Should we move charges of a task when a task is moved into this
  	 * mem_cgroup ? And what type of charges should we move ?
  	 */
  	unsigned long 	move_charge_at_immigrate;

  	/*

  	 * percpu counter.

  	 */

  	struct mem_cgroup_stat_cpu *stat;

  	/*
  	 * used when a cpu is offlined or other synchronizations
  	 * See mem_cgroup_read_stat().
  	 */
  	struct mem_cgroup_stat_cpu nocpu_base;
  	spinlock_t pcp_counter_lock;

  };

  /* Stuffs for move charges at task migration. */
  /*
   * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
   * left-shifted bitmap of these types.
   */
  enum move_type {

  	MOVE_CHARGE_TYPE_ANON,	/* private anonymous page and swap of it */

  	MOVE_CHARGE_TYPE_FILE,	/* file page(including tmpfs) and swap of it */

  	NR_MOVE_TYPE,
  };

  /* "mc" and its members are protected by cgroup_mutex */
  static struct move_charge_struct {

  	spinlock_t	  lock; /* for from, to */

  	struct mem_cgroup *from;
  	struct mem_cgroup *to;
  	unsigned long precharge;

  	unsigned long moved_charge;

  	unsigned long moved_swap;

  	struct task_struct *moving_task;	/* a task moving charges */
  	wait_queue_head_t waitq;		/* a waitq for other context */
  } mc = {

  	.lock = __SPIN_LOCK_UNLOCKED(mc.lock),

  	.waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
  };

  static bool move_anon(void)
  {
  	return test_bit(MOVE_CHARGE_TYPE_ANON,
  					&mc.to->move_charge_at_immigrate);
  }

  static bool move_file(void)
  {
  	return test_bit(MOVE_CHARGE_TYPE_FILE,
  					&mc.to->move_charge_at_immigrate);
  }

  /*
   * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
   * limit reclaim to prevent infinite loops, if they ever occur.
   */
  #define	MEM_CGROUP_MAX_RECLAIM_LOOPS		(100)
  #define	MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS	(2)

  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 */

  	MEM_CGROUP_CHARGE_TYPE_DROP,	/* a page was unused swap cache */

  	NR_CHARGE_TYPE,
  };

  /* only for here (for easy reading.) */
  #define PCGF_CACHE	(1UL << PCG_CACHE)
  #define PCGF_USED	(1UL << PCG_USED)

  #define PCGF_LOCK	(1UL << PCG_LOCK)

  /* Not used, but added here for completeness */
  #define PCGF_ACCT	(1UL << PCG_ACCT)

  /* for encoding cft->private value on file */
  #define _MEM			(0)
  #define _MEMSWAP		(1)

  #define _OOM_TYPE		(2)

  #define MEMFILE_PRIVATE(x, val)	(((x) << 16) | (val))
  #define MEMFILE_TYPE(val)	(((val) >> 16) & 0xffff)
  #define MEMFILE_ATTR(val)	((val) & 0xffff)

  /* Used for OOM nofiier */
  #define OOM_CONTROL		(0)

  /*
   * Reclaim flags for mem_cgroup_hierarchical_reclaim
   */
  #define MEM_CGROUP_RECLAIM_NOSWAP_BIT	0x0
  #define MEM_CGROUP_RECLAIM_NOSWAP	(1 << MEM_CGROUP_RECLAIM_NOSWAP_BIT)
  #define MEM_CGROUP_RECLAIM_SHRINK_BIT	0x1
  #define MEM_CGROUP_RECLAIM_SHRINK	(1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)

  #define MEM_CGROUP_RECLAIM_SOFT_BIT	0x2
  #define MEM_CGROUP_RECLAIM_SOFT		(1 << MEM_CGROUP_RECLAIM_SOFT_BIT)

  static void mem_cgroup_get(struct mem_cgroup *mem);
  static void mem_cgroup_put(struct mem_cgroup *mem);

  static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);

  static void drain_all_stock_async(void);

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

  struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem)
  {
  	return &mem->css;
  }

  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);
  
  	if (!mem)
  		return NULL;
  
  	return mem_cgroup_zoneinfo(mem, nid, zid);
  }
  
  static struct mem_cgroup_tree_per_zone *
  soft_limit_tree_node_zone(int nid, int zid)
  {
  	return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
  }
  
  static struct mem_cgroup_tree_per_zone *
  soft_limit_tree_from_page(struct page *page)
  {
  	int nid = page_to_nid(page);
  	int zid = page_zonenum(page);
  
  	return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
  }
  
  static void

  __mem_cgroup_insert_exceeded(struct mem_cgroup *mem,

  				struct mem_cgroup_per_zone *mz,

  				struct mem_cgroup_tree_per_zone *mctz,
  				unsigned long long new_usage_in_excess)

  {
  	struct rb_node **p = &mctz->rb_root.rb_node;
  	struct rb_node *parent = NULL;
  	struct mem_cgroup_per_zone *mz_node;
  
  	if (mz->on_tree)
  		return;

  	mz->usage_in_excess = new_usage_in_excess;
  	if (!mz->usage_in_excess)
  		return;

  	while (*p) {
  		parent = *p;
  		mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
  					tree_node);
  		if (mz->usage_in_excess < mz_node->usage_in_excess)
  			p = &(*p)->rb_left;
  		/*
  		 * We can't avoid mem cgroups that are over their soft
  		 * limit by the same amount
  		 */
  		else if (mz->usage_in_excess >= mz_node->usage_in_excess)
  			p = &(*p)->rb_right;
  	}
  	rb_link_node(&mz->tree_node, parent, p);
  	rb_insert_color(&mz->tree_node, &mctz->rb_root);
  	mz->on_tree = true;

  }
  
  static void
  __mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
  				struct mem_cgroup_per_zone *mz,
  				struct mem_cgroup_tree_per_zone *mctz)
  {
  	if (!mz->on_tree)
  		return;
  	rb_erase(&mz->tree_node, &mctz->rb_root);
  	mz->on_tree = false;
  }
  
  static void

  mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
  				struct mem_cgroup_per_zone *mz,
  				struct mem_cgroup_tree_per_zone *mctz)
  {
  	spin_lock(&mctz->lock);

  	__mem_cgroup_remove_exceeded(mem, mz, mctz);

  	spin_unlock(&mctz->lock);
  }

  
  static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
  {

  	unsigned long long excess;

  	struct mem_cgroup_per_zone *mz;
  	struct mem_cgroup_tree_per_zone *mctz;

  	int nid = page_to_nid(page);
  	int zid = page_zonenum(page);

  	mctz = soft_limit_tree_from_page(page);
  
  	/*

  	 * Necessary to update all ancestors when hierarchy is used.
  	 * because their event counter is not touched.

  	 */

  	for (; mem; mem = parent_mem_cgroup(mem)) {
  		mz = mem_cgroup_zoneinfo(mem, nid, zid);

  		excess = res_counter_soft_limit_excess(&mem->res);

  		/*
  		 * We have to update the tree if mz is on RB-tree or
  		 * mem is over its softlimit.
  		 */

  		if (excess || mz->on_tree) {

  			spin_lock(&mctz->lock);
  			/* if on-tree, remove it */
  			if (mz->on_tree)
  				__mem_cgroup_remove_exceeded(mem, mz, mctz);
  			/*

  			 * Insert again. mz->usage_in_excess will be updated.
  			 * If excess is 0, no tree ops.

  			 */

  			__mem_cgroup_insert_exceeded(mem, mz, mctz, excess);

  			spin_unlock(&mctz->lock);
  		}

  	}
  }
  
  static void mem_cgroup_remove_from_trees(struct mem_cgroup *mem)
  {
  	int node, zone;
  	struct mem_cgroup_per_zone *mz;
  	struct mem_cgroup_tree_per_zone *mctz;
  
  	for_each_node_state(node, N_POSSIBLE) {
  		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
  			mz = mem_cgroup_zoneinfo(mem, node, zone);
  			mctz = soft_limit_tree_node_zone(node, zone);
  			mem_cgroup_remove_exceeded(mem, mz, mctz);
  		}
  	}
  }

  static inline unsigned long mem_cgroup_get_excess(struct mem_cgroup *mem)
  {
  	return res_counter_soft_limit_excess(&mem->res) >> PAGE_SHIFT;
  }
  
  static struct mem_cgroup_per_zone *
  __mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
  {
  	struct rb_node *rightmost = NULL;

  	struct mem_cgroup_per_zone *mz;

  
  retry:

  	mz = NULL;

  	rightmost = rb_last(&mctz->rb_root);
  	if (!rightmost)
  		goto done;		/* Nothing to reclaim from */
  
  	mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
  	/*
  	 * Remove the node now but someone else can add it back,
  	 * we will to add it back at the end of reclaim to its correct
  	 * position in the tree.
  	 */
  	__mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
  	if (!res_counter_soft_limit_excess(&mz->mem->res) ||
  		!css_tryget(&mz->mem->css))
  		goto retry;
  done:
  	return mz;
  }
  
  static struct mem_cgroup_per_zone *
  mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
  {
  	struct mem_cgroup_per_zone *mz;
  
  	spin_lock(&mctz->lock);
  	mz = __mem_cgroup_largest_soft_limit_node(mctz);
  	spin_unlock(&mctz->lock);
  	return mz;
  }

  /*
   * Implementation Note: reading percpu statistics for memcg.
   *
   * Both of vmstat[] and percpu_counter has threshold and do periodic
   * synchronization to implement "quick" read. There are trade-off between
   * reading cost and precision of value. Then, we may have a chance to implement
   * a periodic synchronizion of counter in memcg's counter.
   *
   * But this _read() function is used for user interface now. The user accounts
   * memory usage by memory cgroup and he _always_ requires exact value because
   * he accounts memory. Even if we provide quick-and-fuzzy read, we always
   * have to visit all online cpus and make sum. So, for now, unnecessary
   * synchronization is not implemented. (just implemented for cpu hotplug)
   *
   * If there are kernel internal actions which can make use of some not-exact
   * value, and reading all cpu value can be performance bottleneck in some
   * common workload, threashold and synchonization as vmstat[] should be
   * implemented.
   */

  static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
  		enum mem_cgroup_stat_index idx)
  {
  	int cpu;
  	s64 val = 0;

  	get_online_cpus();
  	for_each_online_cpu(cpu)

  		val += per_cpu(mem->stat->count[idx], cpu);

  #ifdef CONFIG_HOTPLUG_CPU
  	spin_lock(&mem->pcp_counter_lock);
  	val += mem->nocpu_base.count[idx];
  	spin_unlock(&mem->pcp_counter_lock);
  #endif
  	put_online_cpus();

  	return val;
  }
  
  static s64 mem_cgroup_local_usage(struct mem_cgroup *mem)
  {
  	s64 ret;
  
  	ret = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_RSS);
  	ret += mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_CACHE);
  	return ret;
  }

  static void mem_cgroup_swap_statistics(struct mem_cgroup *mem,
  					 bool charge)
  {
  	int val = (charge) ? 1 : -1;

  	this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_SWAPOUT], val);

  }

  static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
  					 struct page_cgroup *pc,
  					 bool charge)

  {

  	int val = (charge) ? 1 : -1;

  	preempt_disable();

  	if (PageCgroupCache(pc))

  		__this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_CACHE], val);

  	else

  		__this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_RSS], val);

  
  	if (charge)

  		__this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGIN_COUNT]);

  	else

  		__this_cpu_inc(mem->stat->count[MEM_CGROUP_STAT_PGPGOUT_COUNT]);

  	__this_cpu_inc(mem->stat->count[MEM_CGROUP_EVENTS]);

  	preempt_enable();

  }

  static unsigned long mem_cgroup_get_local_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 bool __memcg_event_check(struct mem_cgroup *mem, int event_mask_shift)
  {
  	s64 val;
  
  	val = this_cpu_read(mem->stat->count[MEM_CGROUP_EVENTS]);
  
  	return !(val & ((1 << event_mask_shift) - 1));
  }
  
  /*
   * Check events in order.
   *
   */
  static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
  {
  	/* threshold event is triggered in finer grain than soft limit */
  	if (unlikely(__memcg_event_check(mem, THRESHOLDS_EVENTS_THRESH))) {
  		mem_cgroup_threshold(mem);
  		if (unlikely(__memcg_event_check(mem, SOFTLIMIT_EVENTS_THRESH)))
  			mem_cgroup_update_tree(mem, page);
  	}
  }

  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 struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
  {
  	struct mem_cgroup *mem = NULL;

  
  	if (!mm)
  		return NULL;

  	/*
  	 * Because we have no locks, mm->owner's may be being moved to other
  	 * cgroup. We use css_tryget() here even if this looks
  	 * pessimistic (rather than adding locks here).
  	 */
  	rcu_read_lock();
  	do {
  		mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
  		if (unlikely(!mem))
  			break;
  	} while (!css_tryget(&mem->css));
  	rcu_read_unlock();
  	return mem;
  }

  /* The caller has to guarantee "mem" exists before calling this */
  static struct mem_cgroup *mem_cgroup_start_loop(struct mem_cgroup *mem)

  {

  	struct cgroup_subsys_state *css;
  	int found;
  
  	if (!mem) /* ROOT cgroup has the smallest ID */
  		return root_mem_cgroup; /*css_put/get against root is ignored*/
  	if (!mem->use_hierarchy) {
  		if (css_tryget(&mem->css))
  			return mem;
  		return NULL;
  	}
  	rcu_read_lock();
  	/*
  	 * searching a memory cgroup which has the smallest ID under given
  	 * ROOT cgroup. (ID >= 1)
  	 */
  	css = css_get_next(&mem_cgroup_subsys, 1, &mem->css, &found);
  	if (css && css_tryget(css))
  		mem = container_of(css, struct mem_cgroup, css);
  	else
  		mem = NULL;
  	rcu_read_unlock();
  	return mem;

  }
  
  static struct mem_cgroup *mem_cgroup_get_next(struct mem_cgroup *iter,
  					struct mem_cgroup *root,
  					bool cond)
  {
  	int nextid = css_id(&iter->css) + 1;
  	int found;
  	int hierarchy_used;

  	struct cgroup_subsys_state *css;

  	hierarchy_used = iter->use_hierarchy;

  	css_put(&iter->css);

  	/* If no ROOT, walk all, ignore hierarchy */
  	if (!cond || (root && !hierarchy_used))

  		return NULL;

  	if (!root)
  		root = root_mem_cgroup;

  	do {
  		iter = NULL;

  		rcu_read_lock();

  
  		css = css_get_next(&mem_cgroup_subsys, nextid,
  				&root->css, &found);

  		if (css && css_tryget(css))

  			iter = container_of(css, struct mem_cgroup, css);

  		rcu_read_unlock();

  		/* If css is NULL, no more cgroups will be found */

  		nextid = found + 1;

  	} while (css && !iter);

  	return iter;

  }

  /*
   * for_eacn_mem_cgroup_tree() for visiting all cgroup under tree. Please
   * be careful that "break" loop is not allowed. We have reference count.
   * Instead of that modify "cond" to be false and "continue" to exit the loop.
   */
  #define for_each_mem_cgroup_tree_cond(iter, root, cond)	\
  	for (iter = mem_cgroup_start_loop(root);\
  	     iter != NULL;\
  	     iter = mem_cgroup_get_next(iter, root, cond))
  
  #define for_each_mem_cgroup_tree(iter, root) \
  	for_each_mem_cgroup_tree_cond(iter, root, true)

  #define for_each_mem_cgroup_all(iter) \
  	for_each_mem_cgroup_tree_cond(iter, NULL, true)

  static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
  {
  	return (mem == root_mem_cgroup);
  }

  /*
   * Following LRU functions are allowed to be used without PCG_LOCK.
   * Operations are called by routine of global LRU independently from memcg.
   * What we have to take care of here is validness of pc->mem_cgroup.
   *
   * Changes to pc->mem_cgroup happens when
   * 1. charge
   * 2. moving account
   * In typical case, "charge" is done before add-to-lru. Exception is SwapCache.
   * It is added to LRU before charge.
   * If PCG_USED bit is not set, page_cgroup is not added to this private LRU.
   * When moving account, the page is not on LRU. It's isolated.
   */

  void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
  {
  	struct page_cgroup *pc;

  	struct mem_cgroup_per_zone *mz;

  	if (mem_cgroup_disabled())

  		return;
  	pc = lookup_page_cgroup(page);
  	/* can happen while we handle swapcache. */

  	if (!TestClearPageCgroupAcctLRU(pc))

  		return;

  	VM_BUG_ON(!pc->mem_cgroup);

  	/*
  	 * We don't check PCG_USED bit. It's cleared when the "page" is finally
  	 * removed from global LRU.
  	 */

  	mz = page_cgroup_zoneinfo(pc);

  	MEM_CGROUP_ZSTAT(mz, lru) -= 1;

  	if (mem_cgroup_is_root(pc->mem_cgroup))
  		return;
  	VM_BUG_ON(list_empty(&pc->lru));

  	list_del_init(&pc->lru);

  }

  void mem_cgroup_del_lru(struct page *page)

  {

  	mem_cgroup_del_lru_list(page, page_lru(page));
  }

  void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
  {
  	struct mem_cgroup_per_zone *mz;
  	struct page_cgroup *pc;

  	if (mem_cgroup_disabled())

  		return;

  	pc = lookup_page_cgroup(page);

  	/*
  	 * Used bit is set without atomic ops but after smp_wmb().
  	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
  	 */

  	smp_rmb();

  	/* unused or root page is not rotated. */
  	if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))

  		return;
  	mz = page_cgroup_zoneinfo(pc);
  	list_move(&pc->lru, &mz->lists[lru]);

  }

  void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)

  {

  	struct page_cgroup *pc;
  	struct mem_cgroup_per_zone *mz;

  	if (mem_cgroup_disabled())

  		return;
  	pc = lookup_page_cgroup(page);

  	VM_BUG_ON(PageCgroupAcctLRU(pc));

  	/*
  	 * Used bit is set without atomic ops but after smp_wmb().
  	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
  	 */

  	smp_rmb();
  	if (!PageCgroupUsed(pc))

  		return;

  	mz = page_cgroup_zoneinfo(pc);

  	MEM_CGROUP_ZSTAT(mz, lru) += 1;

  	SetPageCgroupAcctLRU(pc);
  	if (mem_cgroup_is_root(pc->mem_cgroup))
  		return;

  	list_add(&pc->lru, &mz->lists[lru]);
  }

  /*

   * At handling SwapCache, pc->mem_cgroup may be changed while it's linked to
   * lru because the page may.be reused after it's fully uncharged (because of
   * SwapCache behavior).To handle that, unlink page_cgroup from LRU when charge
   * it again. This function is only used to charge SwapCache. It's done under
   * lock_page and expected that zone->lru_lock is never held.

   */

  static void mem_cgroup_lru_del_before_commit_swapcache(struct page *page)

  {

  	unsigned long flags;
  	struct zone *zone = page_zone(page);
  	struct page_cgroup *pc = lookup_page_cgroup(page);
  
  	spin_lock_irqsave(&zone->lru_lock, flags);
  	/*
  	 * Forget old LRU when this page_cgroup is *not* used. This Used bit
  	 * is guarded by lock_page() because the page is SwapCache.
  	 */
  	if (!PageCgroupUsed(pc))
  		mem_cgroup_del_lru_list(page, page_lru(page));
  	spin_unlock_irqrestore(&zone->lru_lock, flags);

  }

  static void mem_cgroup_lru_add_after_commit_swapcache(struct page *page)
  {
  	unsigned long flags;
  	struct zone *zone = page_zone(page);
  	struct page_cgroup *pc = lookup_page_cgroup(page);
  
  	spin_lock_irqsave(&zone->lru_lock, flags);
  	/* link when the page is linked to LRU but page_cgroup isn't */

  	if (PageLRU(page) && !PageCgroupAcctLRU(pc))

  		mem_cgroup_add_lru_list(page, page_lru(page));
  	spin_unlock_irqrestore(&zone->lru_lock, flags);
  }

  void mem_cgroup_move_lists(struct page *page,
  			   enum lru_list from, enum lru_list to)
  {

  	if (mem_cgroup_disabled())

  		return;
  	mem_cgroup_del_lru_list(page, from);
  	mem_cgroup_add_lru_list(page, to);

  }

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

  	struct mem_cgroup *curr = NULL;

  	struct task_struct *p;

  	p = find_lock_task_mm(task);
  	if (!p)
  		return 0;
  	curr = try_get_mem_cgroup_from_mm(p->mm);
  	task_unlock(p);

  	if (!curr)
  		return 0;

  	/*
  	 * We should check use_hierarchy of "mem" not "curr". Because checking
  	 * use_hierarchy of "curr" here make this function true if hierarchy is
  	 * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
  	 * hierarchy(even if use_hierarchy is disabled in "mem").
  	 */
  	if (mem->use_hierarchy)

  		ret = css_is_ancestor(&curr->css, &mem->css);
  	else
  		ret = (curr == mem);
  	css_put(&curr->css);

  	return ret;
  }

  static int calc_inactive_ratio(struct mem_cgroup *memcg, unsigned long *present_pages)

  {
  	unsigned long active;
  	unsigned long inactive;

  	unsigned long gb;
  	unsigned long inactive_ratio;

  	inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_ANON);
  	active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_ANON);

  	gb = (inactive + active) >> (30 - PAGE_SHIFT);
  	if (gb)
  		inactive_ratio = int_sqrt(10 * gb);
  	else
  		inactive_ratio = 1;
  
  	if (present_pages) {
  		present_pages[0] = inactive;
  		present_pages[1] = active;
  	}
  
  	return inactive_ratio;
  }
  
  int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg)
  {
  	unsigned long active;
  	unsigned long inactive;
  	unsigned long present_pages[2];
  	unsigned long inactive_ratio;
  
  	inactive_ratio = calc_inactive_ratio(memcg, present_pages);
  
  	inactive = present_pages[0];
  	active = present_pages[1];
  
  	if (inactive * inactive_ratio < active)

  		return 1;
  
  	return 0;
  }

  int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg)
  {
  	unsigned long active;
  	unsigned long inactive;
  
  	inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE);
  	active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE);
  
  	return (active > inactive);
  }

  unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
  				       struct zone *zone,
  				       enum lru_list lru)
  {

  	int nid = zone_to_nid(zone);

  	int zid = zone_idx(zone);
  	struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid, zid);
  
  	return MEM_CGROUP_ZSTAT(mz, lru);
  }

  struct zone_reclaim_stat *mem_cgroup_get_reclaim_stat(struct mem_cgroup *memcg,
  						      struct zone *zone)
  {

  	int nid = zone_to_nid(zone);

  	int zid = zone_idx(zone);
  	struct mem_cgroup_per_zone *mz = mem_cgroup_zoneinfo(memcg, nid, zid);
  
  	return &mz->reclaim_stat;
  }
  
  struct zone_reclaim_stat *
  mem_cgroup_get_reclaim_stat_from_page(struct page *page)
  {
  	struct page_cgroup *pc;
  	struct mem_cgroup_per_zone *mz;
  
  	if (mem_cgroup_disabled())
  		return NULL;
  
  	pc = lookup_page_cgroup(page);

  	/*
  	 * Used bit is set without atomic ops but after smp_wmb().
  	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
  	 */
  	smp_rmb();
  	if (!PageCgroupUsed(pc))
  		return NULL;

  	mz = page_cgroup_zoneinfo(pc);
  	if (!mz)
  		return NULL;
  
  	return &mz->reclaim_stat;
  }

  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 = zone_to_nid(z);

  	int zid = zone_idx(z);
  	struct mem_cgroup_per_zone *mz;

  	int lru = LRU_FILE * file + active;

  	int ret;

  	BUG_ON(!mem_cont);

  	mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);

  	src = &mz->lists[lru];

  	scan = 0;
  	list_for_each_entry_safe_reverse(pc, tmp, src, lru) {

  		if (scan >= nr_to_scan)

  			break;

  
  		page = pc->page;

  		if (unlikely(!PageCgroupUsed(pc)))
  			continue;

  		if (unlikely(!PageLRU(page)))

  			continue;

  		scan++;

  		ret = __isolate_lru_page(page, mode, file);
  		switch (ret) {
  		case 0:

  			list_move(&page->lru, dst);

  			mem_cgroup_del_lru(page);

  			nr_taken += hpage_nr_pages(page);

  			break;
  		case -EBUSY:
  			/* we don't affect global LRU but rotate in our LRU */
  			mem_cgroup_rotate_lru_list(page, page_lru(page));
  			break;
  		default:
  			break;

  		}
  	}

  	*scanned = scan;

  
  	trace_mm_vmscan_memcg_isolate(0, nr_to_scan, scan, nr_taken,
  				      0, 0, 0, mode);

  	return nr_taken;
  }

  #define mem_cgroup_from_res_counter(counter, member)	\
  	container_of(counter, struct mem_cgroup, member)

  static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
  {
  	if (do_swap_account) {
  		if (res_counter_check_under_limit(&mem->res) &&
  			res_counter_check_under_limit(&mem->memsw))
  			return true;
  	} else
  		if (res_counter_check_under_limit(&mem->res))
  			return true;
  	return false;
  }

  static unsigned int get_swappiness(struct mem_cgroup *memcg)
  {
  	struct cgroup *cgrp = memcg->css.cgroup;
  	unsigned int swappiness;
  
  	/* root ? */
  	if (cgrp->parent == NULL)
  		return vm_swappiness;
  
  	spin_lock(&memcg->reclaim_param_lock);
  	swappiness = memcg->swappiness;
  	spin_unlock(&memcg->reclaim_param_lock);
  
  	return swappiness;
  }

  static void mem_cgroup_start_move(struct mem_cgroup *mem)
  {
  	int cpu;

  
  	get_online_cpus();
  	spin_lock(&mem->pcp_counter_lock);
  	for_each_online_cpu(cpu)

  		per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) += 1;

  	mem->nocpu_base.count[MEM_CGROUP_ON_MOVE] += 1;
  	spin_unlock(&mem->pcp_counter_lock);
  	put_online_cpus();

  
  	synchronize_rcu();
  }
  
  static void mem_cgroup_end_move(struct mem_cgroup *mem)
  {
  	int cpu;
  
  	if (!mem)
  		return;

  	get_online_cpus();
  	spin_lock(&mem->pcp_counter_lock);
  	for_each_online_cpu(cpu)

  		per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) -= 1;

  	mem->nocpu_base.count[MEM_CGROUP_ON_MOVE] -= 1;
  	spin_unlock(&mem->pcp_counter_lock);
  	put_online_cpus();

  }
  /*
   * 2 routines for checking "mem" is under move_account() or not.
   *
   * mem_cgroup_stealed() - checking a cgroup is mc.from or not. This is used
   *			  for avoiding race in accounting. If true,
   *			  pc->mem_cgroup may be overwritten.
   *
   * mem_cgroup_under_move() - checking a cgroup is mc.from or mc.to or
   *			  under hierarchy of moving cgroups. This is for
   *			  waiting at hith-memory prressure caused by "move".
   */
  
  static bool mem_cgroup_stealed(struct mem_cgroup *mem)
  {
  	VM_BUG_ON(!rcu_read_lock_held());
  	return this_cpu_read(mem->stat->count[MEM_CGROUP_ON_MOVE]) > 0;
  }

  
  static bool mem_cgroup_under_move(struct mem_cgroup *mem)
  {

  	struct mem_cgroup *from;
  	struct mem_cgroup *to;

  	bool ret = false;

  	/*
  	 * Unlike task_move routines, we access mc.to, mc.from not under
  	 * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.
  	 */
  	spin_lock(&mc.lock);
  	from = mc.from;
  	to = mc.to;
  	if (!from)
  		goto unlock;
  	if (from == mem || to == mem
  	    || (mem->use_hierarchy && css_is_ancestor(&from->css, &mem->css))
  	    || (mem->use_hierarchy && css_is_ancestor(&to->css,	&mem->css)))
  		ret = true;
  unlock:
  	spin_unlock(&mc.lock);

  	return ret;
  }
  
  static bool mem_cgroup_wait_acct_move(struct mem_cgroup *mem)
  {
  	if (mc.moving_task && current != mc.moving_task) {
  		if (mem_cgroup_under_move(mem)) {
  			DEFINE_WAIT(wait);
  			prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
  			/* moving charge context might have finished. */
  			if (mc.moving_task)
  				schedule();
  			finish_wait(&mc.waitq, &wait);
  			return true;
  		}
  	}
  	return false;
  }

  /**

   * mem_cgroup_print_oom_info: Called from OOM with tasklist_lock held in read mode.

   * @memcg: The memory cgroup that went over limit
   * @p: Task that is going to be killed
   *
   * NOTE: @memcg and @p's mem_cgroup can be different when hierarchy is
   * enabled
   */
  void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
  {
  	struct cgroup *task_cgrp;
  	struct cgroup *mem_cgrp;
  	/*
  	 * Need a buffer in BSS, can't rely on allocations. The code relies
  	 * on the assumption that OOM is serialized for memory controller.
  	 * If this assumption is broken, revisit this code.
  	 */
  	static char memcg_name[PATH_MAX];
  	int ret;

  	if (!memcg || !p)

  		return;
  
  
  	rcu_read_lock();
  
  	mem_cgrp = memcg->css.cgroup;
  	task_cgrp = task_cgroup(p, mem_cgroup_subsys_id);
  
  	ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
  	if (ret < 0) {
  		/*
  		 * Unfortunately, we are unable to convert to a useful name
  		 * But we'll still print out the usage information
  		 */
  		rcu_read_unlock();
  		goto done;
  	}
  	rcu_read_unlock();
  
  	printk(KERN_INFO "Task in %s killed", memcg_name);
  
  	rcu_read_lock();
  	ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
  	if (ret < 0) {
  		rcu_read_unlock();
  		goto done;
  	}
  	rcu_read_unlock();
  
  	/*
  	 * Continues from above, so we don't need an KERN_ level
  	 */
  	printk(KERN_CONT " as a result of limit of %s
  ", memcg_name);
  done:
  
  	printk(KERN_INFO "memory: usage %llukB, limit %llukB, failcnt %llu
  ",
  		res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
  		res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
  		res_counter_read_u64(&memcg->res, RES_FAILCNT));
  	printk(KERN_INFO "memory+swap: usage %llukB, limit %llukB, "
  		"failcnt %llu
  ",
  		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
  		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
  		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
  }

  /*
   * This function returns the number of memcg under hierarchy tree. Returns
   * 1(self count) if no children.
   */
  static int mem_cgroup_count_children(struct mem_cgroup *mem)
  {
  	int num = 0;

  	struct mem_cgroup *iter;
  
  	for_each_mem_cgroup_tree(iter, mem)
  		num++;

  	return num;
  }

  /*

   * Return the memory (and swap, if configured) limit for a memcg.
   */
  u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
  {
  	u64 limit;
  	u64 memsw;

  	limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
  	limit += total_swap_pages << PAGE_SHIFT;

  	memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
  	/*
  	 * If memsw is finite and limits the amount of swap space available
  	 * to this memcg, return that limit.
  	 */
  	return min(limit, memsw);
  }
  
  /*

   * Visit the first child (need not be the first child as per the ordering
   * of the cgroup list, since we track last_scanned_child) of @mem and use
   * that to reclaim free pages from.
   */
  static struct mem_cgroup *
  mem_cgroup_select_victim(struct mem_cgroup *root_mem)
  {
  	struct mem_cgroup *ret = NULL;
  	struct cgroup_subsys_state *css;
  	int nextid, found;
  
  	if (!root_mem->use_hierarchy) {
  		css_get(&root_mem->css);
  		ret = root_mem;
  	}
  
  	while (!ret) {
  		rcu_read_lock();
  		nextid = root_mem->last_scanned_child + 1;
  		css = css_get_next(&mem_cgroup_subsys, nextid, &root_mem->css,
  				   &found);
  		if (css && css_tryget(css))
  			ret = container_of(css, struct mem_cgroup, css);
  
  		rcu_read_unlock();
  		/* Updates scanning parameter */
  		spin_lock(&root_mem->reclaim_param_lock);
  		if (!css) {
  			/* this means start scan from ID:1 */
  			root_mem->last_scanned_child = 0;
  		} else
  			root_mem->last_scanned_child = found;
  		spin_unlock(&root_mem->reclaim_param_lock);
  	}
  
  	return ret;
  }
  
  /*
   * Scan the hierarchy if needed to reclaim memory. We remember the last child
   * we reclaimed from, so that we don't end up penalizing one child extensively
   * based on its position in the children list.

   *
   * root_mem is the original ancestor that we've been reclaim from.

   *
   * We give up and return to the caller when we visit root_mem twice.
   * (other groups can be removed while we're walking....)

   *
   * If shrink==true, for avoiding to free too much, this returns immedieately.

   */
  static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,

  						struct zone *zone,

  						gfp_t gfp_mask,
  						unsigned long reclaim_options)

  {

  	struct mem_cgroup *victim;
  	int ret, total = 0;
  	int loop = 0;

  	bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP;
  	bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;

  	bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
  	unsigned long excess = mem_cgroup_get_excess(root_mem);

  	/* If memsw_is_minimum==1, swap-out is of-no-use. */
  	if (root_mem->memsw_is_minimum)
  		noswap = true;

  	while (1) {

  		victim = mem_cgroup_select_victim(root_mem);

  		if (victim == root_mem) {

  			loop++;

  			if (loop >= 1)
  				drain_all_stock_async();

  			if (loop >= 2) {
  				/*
  				 * If we have not been able to reclaim
  				 * anything, it might because there are
  				 * no reclaimable pages under this hierarchy
  				 */
  				if (!check_soft || !total) {
  					css_put(&victim->css);
  					break;
  				}
  				/*
  				 * We want to do more targetted reclaim.
  				 * excess >> 2 is not to excessive so as to
  				 * reclaim too much, nor too less that we keep
  				 * coming back to reclaim from this cgroup
  				 */
  				if (total >= (excess >> 2) ||
  					(loop > MEM_CGROUP_MAX_RECLAIM_LOOPS)) {
  					css_put(&victim->css);
  					break;
  				}
  			}
  		}

  		if (!mem_cgroup_local_usage(victim)) {

  			/* this cgroup's local usage == 0 */
  			css_put(&victim->css);

  			continue;
  		}

  		/* we use swappiness of local cgroup */

  		if (check_soft)
  			ret = mem_cgroup_shrink_node_zone(victim, gfp_mask,

  				noswap, get_swappiness(victim), zone);

  		else
  			ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
  						noswap, get_swappiness(victim));

  		css_put(&victim->css);

  		/*
  		 * At shrinking usage, we can't check we should stop here or
  		 * reclaim more. It's depends on callers. last_scanned_child
  		 * will work enough for keeping fairness under tree.
  		 */
  		if (shrink)
  			return ret;

  		total += ret;

  		if (check_soft) {
  			if (res_counter_check_under_soft_limit(&root_mem->res))
  				return total;
  		} else if (mem_cgroup_check_under_limit(root_mem))

  			return 1 + total;

  	}

  	return total;

  }

  /*
   * Check OOM-Killer is already running under our hierarchy.
   * If someone is running, return false.
   */
  static bool mem_cgroup_oom_lock(struct mem_cgroup *mem)
  {

  	int x, lock_count = 0;
  	struct mem_cgroup *iter;

  	for_each_mem_cgroup_tree(iter, mem) {
  		x = atomic_inc_return(&iter->oom_lock);
  		lock_count = max(x, lock_count);
  	}

  
  	if (lock_count == 1)
  		return true;
  	return false;

  }

  static int mem_cgroup_oom_unlock(struct mem_cgroup *mem)

  {

  	struct mem_cgroup *iter;

  	/*
  	 * When a new child is created while the hierarchy is under oom,
  	 * mem_cgroup_oom_lock() may not be called. We have to use
  	 * atomic_add_unless() here.
  	 */

  	for_each_mem_cgroup_tree(iter, mem)
  		atomic_add_unless(&iter->oom_lock, -1, 0);

  	return 0;
  }

  
  static DEFINE_MUTEX(memcg_oom_mutex);
  static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);

  struct oom_wait_info {
  	struct mem_cgroup *mem;
  	wait_queue_t	wait;
  };
  
  static int memcg_oom_wake_function(wait_queue_t *wait,
  	unsigned mode, int sync, void *arg)
  {
  	struct mem_cgroup *wake_mem = (struct mem_cgroup *)arg;
  	struct oom_wait_info *oom_wait_info;
  
  	oom_wait_info = container_of(wait, struct oom_wait_info, wait);
  
  	if (oom_wait_info->mem == wake_mem)
  		goto wakeup;
  	/* if no hierarchy, no match */
  	if (!oom_wait_info->mem->use_hierarchy || !wake_mem->use_hierarchy)
  		return 0;
  	/*
  	 * Both of oom_wait_info->mem and wake_mem are stable under us.
  	 * Then we can use css_is_ancestor without taking care of RCU.
  	 */
  	if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
  	    !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
  		return 0;
  
  wakeup:
  	return autoremove_wake_function(wait, mode, sync, arg);
  }
  
  static void memcg_wakeup_oom(struct mem_cgroup *mem)
  {
  	/* for filtering, pass "mem" as argument. */
  	__wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, mem);
  }

  static void memcg_oom_recover(struct mem_cgroup *mem)
  {

  	if (mem && atomic_read(&mem->oom_lock))

  		memcg_wakeup_oom(mem);
  }

  /*
   * try to call OOM killer. returns false if we should exit memory-reclaim loop.
   */
  bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)

  {

  	struct oom_wait_info owait;

  	bool locked, need_to_kill;

  	owait.mem = mem;
  	owait.wait.flags = 0;
  	owait.wait.func = memcg_oom_wake_function;
  	owait.wait.private = current;
  	INIT_LIST_HEAD(&owait.wait.task_list);

  	need_to_kill = true;

  	/* At first, try to OOM lock hierarchy under mem.*/
  	mutex_lock(&memcg_oom_mutex);
  	locked = mem_cgroup_oom_lock(mem);
  	/*
  	 * Even if signal_pending(), we can't quit charge() loop without
  	 * accounting. So, UNINTERRUPTIBLE is appropriate. But SIGKILL
  	 * under OOM is always welcomed, use TASK_KILLABLE here.
  	 */

  	prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
  	if (!locked || mem->oom_kill_disable)
  		need_to_kill = false;
  	if (locked)

  		mem_cgroup_oom_notify(mem);

  	mutex_unlock(&memcg_oom_mutex);

  	if (need_to_kill) {
  		finish_wait(&memcg_oom_waitq, &owait.wait);

  		mem_cgroup_out_of_memory(mem, mask);

  	} else {

  		schedule();

  		finish_wait(&memcg_oom_waitq, &owait.wait);

  	}
  	mutex_lock(&memcg_oom_mutex);
  	mem_cgroup_oom_unlock(mem);

  	memcg_wakeup_oom(mem);

  	mutex_unlock(&memcg_oom_mutex);
  
  	if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
  		return false;
  	/* Give chance to dying process */
  	schedule_timeout(1);
  	return true;

  }

  /*
   * Currently used to update mapped file statistics, but the routine can be
   * generalized to update other statistics as well.

   *
   * Notes: Race condition
   *
   * We usually use page_cgroup_lock() for accessing page_cgroup member but
   * it tends to be costly. But considering some conditions, we doesn't need
   * to do so _always_.
   *
   * Considering "charge", lock_page_cgroup() is not required because all
   * file-stat operations happen after a page is attached to radix-tree. There
   * are no race with "charge".
   *
   * Considering "uncharge", we know that memcg doesn't clear pc->mem_cgroup
   * at "uncharge" intentionally. So, we always see valid pc->mem_cgroup even
   * if there are race with "uncharge". Statistics itself is properly handled
   * by flags.
   *
   * Considering "move", this is an only case we see a race. To make the race
   * small, we check MEM_CGROUP_ON_MOVE percpu value and detect there are
   * possibility of race condition. If there is, we take a lock.

   */

  void mem_cgroup_update_page_stat(struct page *page,
  				 enum mem_cgroup_page_stat_item idx, int val)

  {
  	struct mem_cgroup *mem;

  	struct page_cgroup *pc = lookup_page_cgroup(page);
  	bool need_unlock = false;

  	unsigned long uninitialized_var(flags);

  	if (unlikely(!pc))
  		return;

  	rcu_read_lock();

  	mem = pc->mem_cgroup;

  	if (unlikely(!mem || !PageCgroupUsed(pc)))
  		goto out;
  	/* pc->mem_cgroup is unstable ? */
  	if (unlikely(mem_cgroup_stealed(mem))) {
  		/* take a lock against to access pc->mem_cgroup */

  		move_lock_page_cgroup(pc, &flags);

  		need_unlock = true;
  		mem = pc->mem_cgroup;
  		if (!mem || !PageCgroupUsed(pc))
  			goto out;
  	}

  	switch (idx) {

  	case MEMCG_NR_FILE_MAPPED:

  		if (val > 0)
  			SetPageCgroupFileMapped(pc);
  		else if (!page_mapped(page))

  			ClearPageCgroupFileMapped(pc);

  		idx = MEM_CGROUP_STAT_FILE_MAPPED;

  		break;
  	default:
  		BUG();

  	}

  	this_cpu_add(mem->stat->count[idx], val);

  out:
  	if (unlikely(need_unlock))

  		move_unlock_page_cgroup(pc, &flags);

  	rcu_read_unlock();
  	return;

  }

  EXPORT_SYMBOL(mem_cgroup_update_page_stat);

  /*

   * size of first charge trial. "32" comes from vmscan.c's magic value.
   * TODO: maybe necessary to use big numbers in big irons.
   */
  #define CHARGE_SIZE	(32 * PAGE_SIZE)
  struct memcg_stock_pcp {
  	struct mem_cgroup *cached; /* this never be root cgroup */
  	int charge;
  	struct work_struct work;
  };
  static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
  static atomic_t memcg_drain_count;
  
  /*
   * Try to consume stocked charge on this cpu. If success, PAGE_SIZE is consumed
   * from local stock and true is returned. If the stock is 0 or charges from a
   * cgroup which is not current target, returns false. This stock will be
   * refilled.
   */
  static bool consume_stock(struct mem_cgroup *mem)
  {
  	struct memcg_stock_pcp *stock;
  	bool ret = true;
  
  	stock = &get_cpu_var(memcg_stock);
  	if (mem == stock->cached && stock->charge)
  		stock->charge -= PAGE_SIZE;
  	else /* need to call res_counter_charge */
  		ret = false;
  	put_cpu_var(memcg_stock);
  	return ret;
  }
  
  /*
   * Returns stocks cached in percpu to res_counter and reset cached information.
   */
  static void drain_stock(struct memcg_stock_pcp *stock)
  {
  	struct mem_cgroup *old = stock->cached;
  
  	if (stock->charge) {
  		res_counter_uncharge(&old->res, stock->charge);
  		if (do_swap_account)
  			res_counter_uncharge(&old->memsw, stock->charge);
  	}
  	stock->cached = NULL;
  	stock->charge = 0;
  }
  
  /*
   * This must be called under preempt disabled or must be called by
   * a thread which is pinned to local cpu.
   */
  static void drain_local_stock(struct work_struct *dummy)
  {
  	struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock);
  	drain_stock(stock);
  }
  
  /*
   * Cache charges(val) which is from res_counter, to local per_cpu area.

   * This will be consumed by consume_stock() function, later.

   */
  static void refill_stock(struct mem_cgroup *mem, int val)
  {
  	struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
  
  	if (stock->cached != mem) { /* reset if necessary */
  		drain_stock(stock);
  		stock->cached = mem;
  	}
  	stock->charge += val;
  	put_cpu_var(memcg_stock);
  }
  
  /*
   * Tries to drain stocked charges in other cpus. This function is asynchronous
   * and just put a work per cpu for draining localy on each cpu. Caller can
   * expects some charges will be back to res_counter later but cannot wait for
   * it.
   */
  static void drain_all_stock_async(void)
  {
  	int cpu;
  	/* This function is for scheduling "drain" in asynchronous way.
  	 * The result of "drain" is not directly handled by callers. Then,
  	 * if someone is calling drain, we don't have to call drain more.
  	 * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if
  	 * there is a race. We just do loose check here.
  	 */
  	if (atomic_read(&memcg_drain_count))
  		return;
  	/* Notify other cpus that system-wide "drain" is running */
  	atomic_inc(&memcg_drain_count);
  	get_online_cpus();
  	for_each_online_cpu(cpu) {
  		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
  		schedule_work_on(cpu, &stock->work);
  	}
   	put_online_cpus();
  	atomic_dec(&memcg_drain_count);
  	/* We don't wait for flush_work */
  }
  
  /* This is a synchronous drain interface. */
  static void drain_all_stock_sync(void)
  {
  	/* called when force_empty is called */
  	atomic_inc(&memcg_drain_count);
  	schedule_on_each_cpu(drain_local_stock);
  	atomic_dec(&memcg_drain_count);
  }

  /*
   * This function drains percpu counter value from DEAD cpu and
   * move it to local cpu. Note that this function can be preempted.
   */
  static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *mem, int cpu)
  {
  	int i;
  
  	spin_lock(&mem->pcp_counter_lock);
  	for (i = 0; i < MEM_CGROUP_STAT_DATA; i++) {
  		s64 x = per_cpu(mem->stat->count[i], cpu);
  
  		per_cpu(mem->stat->count[i], cpu) = 0;
  		mem->nocpu_base.count[i] += x;
  	}

  	/* need to clear ON_MOVE value, works as a kind of lock. */
  	per_cpu(mem->stat->count[MEM_CGROUP_ON_MOVE], cpu) = 0;
  	spin_unlock(&mem->pcp_counter_lock);
  }
  
  static void synchronize_mem_cgroup_on_move(struct mem_cgroup *mem, int cpu)
  {
  	int idx = MEM_CGROUP_ON_MOVE;
  
  	spin_lock(&mem->pcp_counter_lock);
  	per_cpu(mem->stat->count[idx], cpu) = mem->nocpu_base.count[idx];

  	spin_unlock(&mem->pcp_counter_lock);
  }
  
  static int __cpuinit memcg_cpu_hotplug_callback(struct notifier_block *nb,

  					unsigned long action,
  					void *hcpu)
  {
  	int cpu = (unsigned long)hcpu;
  	struct memcg_stock_pcp *stock;

  	struct mem_cgroup *iter;

  	if ((action == CPU_ONLINE)) {
  		for_each_mem_cgroup_all(iter)
  			synchronize_mem_cgroup_on_move(iter, cpu);
  		return NOTIFY_OK;
  	}

  	if ((action != CPU_DEAD) || action != CPU_DEAD_FROZEN)

  		return NOTIFY_OK;

  
  	for_each_mem_cgroup_all(iter)
  		mem_cgroup_drain_pcp_counter(iter, cpu);

  	stock = &per_cpu(memcg_stock, cpu);
  	drain_stock(stock);
  	return NOTIFY_OK;
  }

  
  /* See __mem_cgroup_try_charge() for details */
  enum {
  	CHARGE_OK,		/* success */
  	CHARGE_RETRY,		/* need to retry but retry is not bad */
  	CHARGE_NOMEM,		/* we can't do more. return -ENOMEM */
  	CHARGE_WOULDBLOCK,	/* GFP_WAIT wasn't set and no enough res. */
  	CHARGE_OOM_DIE,		/* the current is killed because of OOM */
  };
  
  static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
  				int csize, bool oom_check)
  {
  	struct mem_cgroup *mem_over_limit;
  	struct res_counter *fail_res;
  	unsigned long flags = 0;
  	int ret;
  
  	ret = res_counter_charge(&mem->res, csize, &fail_res);
  
  	if (likely(!ret)) {
  		if (!do_swap_account)
  			return CHARGE_OK;
  		ret = res_counter_charge(&mem->memsw, csize, &fail_res);
  		if (likely(!ret))
  			return CHARGE_OK;
  
  		mem_over_limit = mem_cgroup_from_res_counter(fail_res, memsw);
  		flags |= MEM_CGROUP_RECLAIM_NOSWAP;
  	} else
  		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
  
  	if (csize > PAGE_SIZE) /* change csize and retry */
  		return CHARGE_RETRY;
  
  	if (!(gfp_mask & __GFP_WAIT))
  		return CHARGE_WOULDBLOCK;
  
  	ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
  					gfp_mask, flags);
  	/*
  	 * 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 (ret || mem_cgroup_check_under_limit(mem_over_limit))
  		return CHARGE_RETRY;
  
  	/*
  	 * At task move, charge accounts can be doubly counted. So, it's
  	 * better to wait until the end of task_move if something is going on.
  	 */
  	if (mem_cgroup_wait_acct_move(mem_over_limit))
  		return CHARGE_RETRY;
  
  	/* If we don't need to call oom-killer at el, return immediately */
  	if (!oom_check)
  		return CHARGE_NOMEM;
  	/* check OOM */
  	if (!mem_cgroup_handle_oom(mem_over_limit, gfp_mask))
  		return CHARGE_OOM_DIE;
  
  	return CHARGE_RETRY;
  }

  /*

   * 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,
  				   int page_size)

  {

  	int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
  	struct mem_cgroup *mem = NULL;
  	int ret;

  	int csize = max(CHARGE_SIZE, (unsigned long) page_size);

  	/*
  	 * Unlike gloval-vm's OOM-kill, we're not in memory shortage
  	 * in system level. So, allow to go ahead dying process in addition to
  	 * MEMDIE process.
  	 */
  	if (unlikely(test_thread_flag(TIF_MEMDIE)
  		     || fatal_signal_pending(current)))
  		goto bypass;

  	/*

  	 * 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 (!*memcg && !mm)
  		goto bypass;
  again:
  	if (*memcg) { /* css should be a valid one */

  		mem = *memcg;

  		VM_BUG_ON(css_is_removed(&mem->css));
  		if (mem_cgroup_is_root(mem))
  			goto done;

  		if (page_size == PAGE_SIZE && consume_stock(mem))

  			goto done;

  		css_get(&mem->css);
  	} else {

  		struct task_struct *p;

  		rcu_read_lock();
  		p = rcu_dereference(mm->owner);

  		/*

  		 * Because we don't have task_lock(), "p" can exit.
  		 * In that case, "mem" can point to root or p can be NULL with
  		 * race with swapoff. Then, we have small risk of mis-accouning.
  		 * But such kind of mis-account by race always happens because
  		 * we don't have cgroup_mutex(). It's overkill and we allo that
  		 * small race, here.
  		 * (*) swapoff at el will charge against mm-struct not against
  		 * task-struct. So, mm->owner can be NULL.

  		 */
  		mem = mem_cgroup_from_task(p);

  		if (!mem || mem_cgroup_is_root(mem)) {

  			rcu_read_unlock();
  			goto done;
  		}

  		if (page_size == PAGE_SIZE && consume_stock(mem)) {

  			/*
  			 * It seems dagerous to access memcg without css_get().
  			 * But considering how consume_stok works, it's not
  			 * necessary. If consume_stock success, some charges
  			 * from this memcg are cached on this cpu. So, we
  			 * don't need to call css_get()/css_tryget() before
  			 * calling consume_stock().
  			 */
  			rcu_read_unlock();
  			goto done;
  		}
  		/* after here, we may be blocked. we need to get refcnt */
  		if (!css_tryget(&mem->css)) {
  			rcu_read_unlock();
  			goto again;
  		}
  		rcu_read_unlock();
  	}

  	do {
  		bool oom_check;

  		/* If killed, bypass charge */

  		if (fatal_signal_pending(current)) {
  			css_put(&mem->css);

  			goto bypass;

  		}

  		oom_check = false;
  		if (oom && !nr_oom_retries) {
  			oom_check = true;
  			nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;

  		}

  		ret = __mem_cgroup_do_charge(mem, gfp_mask, csize, oom_check);

  		switch (ret) {
  		case CHARGE_OK:
  			break;
  		case CHARGE_RETRY: /* not in OOM situation but retry */

  			csize = page_size;

  			css_put(&mem->css);
  			mem = NULL;
  			goto again;

  		case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */

  			css_put(&mem->css);

  			goto nomem;
  		case CHARGE_NOMEM: /* OOM routine works */

  			if (!oom) {
  				css_put(&mem->css);

  				goto nomem;

  			}

  			/* If oom, we never return -ENOMEM */
  			nr_oom_retries--;
  			break;
  		case CHARGE_OOM_DIE: /* Killed by OOM Killer */

  			css_put(&mem->css);

  			goto bypass;

  		}

  	} while (ret != CHARGE_OK);

  	if (csize > page_size)
  		refill_stock(mem, csize - page_size);

  	css_put(&mem->css);

  done:

  	*memcg = mem;

  	return 0;
  nomem:

  	*memcg = NULL;

  	return -ENOMEM;

  bypass:
  	*memcg = NULL;
  	return 0;

  }

  /*

   * Somemtimes we have to undo a charge we got by try_charge().
   * This function is for that and do uncharge, put css's refcnt.
   * gotten by try_charge().
   */

  static void __mem_cgroup_cancel_charge(struct mem_cgroup *mem,
  							unsigned long count)

  {
  	if (!mem_cgroup_is_root(mem)) {

  		res_counter_uncharge(&mem->res, PAGE_SIZE * count);

  		if (do_swap_account)

  			res_counter_uncharge(&mem->memsw, PAGE_SIZE * count);

  	}

  }

  static void mem_cgroup_cancel_charge(struct mem_cgroup *mem,
  				     int page_size)

  {

  	__mem_cgroup_cancel_charge(mem, page_size >> PAGE_SHIFT);

  }
  
  /*

   * A helper function to get mem_cgroup from ID. must be called under
   * rcu_read_lock(). The caller must check css_is_removed() or some if
   * it's concern. (dropping refcnt from swap can be called against removed
   * memcg.)
   */
  static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
  {
  	struct cgroup_subsys_state *css;
  
  	/* ID 0 is unused ID */
  	if (!id)
  		return NULL;
  	css = css_lookup(&mem_cgroup_subsys, id);
  	if (!css)
  		return NULL;
  	return container_of(css, struct mem_cgroup, css);
  }

  struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)

  {

  	struct mem_cgroup *mem = NULL;

  	struct page_cgroup *pc;

  	unsigned short id;

  	swp_entry_t ent;

  	VM_BUG_ON(!PageLocked(page));

  	pc = lookup_page_cgroup(page);

  	lock_page_cgroup(pc);

  	if (PageCgroupUsed(pc)) {

  		mem = pc->mem_cgroup;

  		if (mem && !css_tryget(&mem->css))
  			mem = NULL;

  	} else if (PageSwapCache(page)) {

  		ent.val = page_private(page);

  		id = lookup_swap_cgroup(ent);
  		rcu_read_lock();
  		mem = mem_cgroup_lookup(id);
  		if (mem && !css_tryget(&mem->css))
  			mem = NULL;
  		rcu_read_unlock();

  	}

  	unlock_page_cgroup(pc);

  	return mem;
  }

  /*

   * 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)

  {

  	pc->mem_cgroup = mem;

  	/*
  	 * We access a page_cgroup asynchronously without lock_page_cgroup().
  	 * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
  	 * is accessed after testing USED bit. To make pc->mem_cgroup visible
  	 * before USED bit, we need memory barrier here.
  	 * See mem_cgroup_add_lru_list(), etc.
   	 */

  	smp_wmb();

  	switch (ctype) {
  	case MEM_CGROUP_CHARGE_TYPE_CACHE:
  	case MEM_CGROUP_CHARGE_TYPE_SHMEM:
  		SetPageCgroupCache(pc);
  		SetPageCgroupUsed(pc);
  		break;
  	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
  		ClearPageCgroupCache(pc);
  		SetPageCgroupUsed(pc);
  		break;
  	default:
  		break;
  	}

  	mem_cgroup_charge_statistics(mem, pc, true);

  }
  
  static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
  				       struct page_cgroup *pc,
  				       enum charge_type ctype,
  				       int page_size)
  {
  	int i;
  	int count = page_size >> PAGE_SHIFT;
  
  	/* 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);
  		mem_cgroup_cancel_charge(mem, page_size);
  		return;
  	}
  
  	/*
  	 * we don't need page_cgroup_lock about tail pages, becase they are not
  	 * accessed by any other context at this point.
  	 */
  	for (i = 0; i < count; i++)
  		____mem_cgroup_commit_charge(mem, pc + i, ctype);

  	unlock_page_cgroup(pc);

  	/*
  	 * "charge_statistics" updated event counter. Then, check it.
  	 * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
  	 * if they exceeds softlimit.
  	 */

  	memcg_check_events(mem, pc->page);

  }

  /**

   * __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.

   * @uncharge: whether we should call uncharge and css_put against @from.

   *
   * The caller must confirm following.

   * - page is not on LRU (isolate_page() is useful.)

   * - the pc is locked, used, and ->mem_cgroup points to @from.

   *

   * This function doesn't do "charge" nor css_get to new cgroup. It should be
   * done by a caller(__mem_cgroup_try_charge would be usefull). If @uncharge is
   * true, this function does "uncharge" from old cgroup, but it doesn't if
   * @uncharge is false, so a caller should do "uncharge".

   */

  static void __mem_cgroup_move_account(struct page_cgroup *pc,

  	struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)

  {

  	VM_BUG_ON(from == to);

  	VM_BUG_ON(PageLRU(pc->page));

  	VM_BUG_ON(!page_is_cgroup_locked(pc));

  	VM_BUG_ON(!PageCgroupUsed(pc));
  	VM_BUG_ON(pc->mem_cgroup != from);

  	if (PageCgroupFileMapped(pc)) {

  		/* Update mapped_file data for mem_cgroup */
  		preempt_disable();
  		__this_cpu_dec(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
  		__this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
  		preempt_enable();

  	}

  	mem_cgroup_charge_statistics(from, pc, false);
  	if (uncharge)
  		/* This is not "cancel", but cancel_charge does all we need. */

  		mem_cgroup_cancel_charge(from, PAGE_SIZE);

  	/* caller should have done css_get */

  	pc->mem_cgroup = to;
  	mem_cgroup_charge_statistics(to, pc, true);

  	/*
  	 * We charges against "to" which may not have any tasks. Then, "to"
  	 * can be under rmdir(). But in current implementation, caller of