diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a9559b9..a2c7bcb 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -526,18 +526,14 @@
 
 static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 {
-	/*
-	 * The ID of the root cgroup is 0, but memcg treat 0 as an
-	 * invalid ID, so we return (cgroup_id + 1).
-	 */
-	return memcg->css.cgroup->id + 1;
+	return memcg->css.id;
 }
 
 static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 {
 	struct cgroup_subsys_state *css;
 
-	css = css_from_id(id - 1, &memory_cgrp_subsys);
+	css = css_from_id(id, &memory_cgrp_subsys);
 	return mem_cgroup_from_css(css);
 }
 
@@ -570,7 +566,8 @@
 		memcg = mem_cgroup_from_task(current);
 		cg_proto = sk->sk_prot->proto_cgroup(memcg);
 		if (!mem_cgroup_is_root(memcg) &&
-		    memcg_proto_active(cg_proto) && css_tryget(&memcg->css)) {
+		    memcg_proto_active(cg_proto) &&
+		    css_tryget_online(&memcg->css)) {
 			sk->sk_cgrp = cg_proto;
 		}
 		rcu_read_unlock();
@@ -831,7 +828,7 @@
 	 */
 	__mem_cgroup_remove_exceeded(mz, mctz);
 	if (!res_counter_soft_limit_excess(&mz->memcg->res) ||
-		!css_tryget(&mz->memcg->css))
+	    !css_tryget_online(&mz->memcg->css))
 		goto retry;
 done:
 	return mz;
@@ -1073,7 +1070,7 @@
 			if (unlikely(!memcg))
 				memcg = root_mem_cgroup;
 		}
-	} while (!css_tryget(&memcg->css));
+	} while (!css_tryget_online(&memcg->css));
 	rcu_read_unlock();
 	return memcg;
 }
@@ -1110,7 +1107,8 @@
 	 */
 	if (next_css) {
 		if ((next_css == &root->css) ||
-		    ((next_css->flags & CSS_ONLINE) && css_tryget(next_css)))
+		    ((next_css->flags & CSS_ONLINE) &&
+		     css_tryget_online(next_css)))
 			return mem_cgroup_from_css(next_css);
 
 		prev_css = next_css;
@@ -1156,7 +1154,7 @@
 		 * would be returned all the time.
 		 */
 		if (position && position != root &&
-				!css_tryget(&position->css))
+		    !css_tryget_online(&position->css))
 			position = NULL;
 	}
 	return position;
@@ -1533,7 +1531,7 @@
 int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 {
 	/* root ? */
-	if (mem_cgroup_disabled() || !css_parent(&memcg->css))
+	if (mem_cgroup_disabled() || !memcg->css.parent)
 		return vm_swappiness;
 
 	return memcg->swappiness;
@@ -2769,9 +2767,9 @@
 
 /*
  * A helper function to get mem_cgroup from ID. must be called under
- * rcu_read_lock().  The caller is responsible for calling css_tryget if
- * the mem_cgroup is used for charging. (dropping refcnt from swap can be
- * called against removed memcg.)
+ * rcu_read_lock().  The caller is responsible for calling
+ * css_tryget_online() if the mem_cgroup is used for charging. (dropping
+ * refcnt from swap can be called against removed memcg.)
  */
 static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
 {
@@ -2794,14 +2792,14 @@
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
 		memcg = pc->mem_cgroup;
-		if (memcg && !css_tryget(&memcg->css))
+		if (memcg && !css_tryget_online(&memcg->css))
 			memcg = NULL;
 	} else if (PageSwapCache(page)) {
 		ent.val = page_private(page);
 		id = lookup_swap_cgroup_id(ent);
 		rcu_read_lock();
 		memcg = mem_cgroup_lookup(id);
-		if (memcg && !css_tryget(&memcg->css))
+		if (memcg && !css_tryget_online(&memcg->css))
 			memcg = NULL;
 		rcu_read_unlock();
 	}
@@ -3365,7 +3363,7 @@
 	}
 
 	/* The corresponding put will be done in the workqueue. */
-	if (!css_tryget(&memcg->css))
+	if (!css_tryget_online(&memcg->css))
 		goto out;
 	rcu_read_unlock();
 
@@ -4125,8 +4123,8 @@
 	memcg = mem_cgroup_lookup(id);
 	if (memcg) {
 		/*
-		 * We uncharge this because swap is freed.
-		 * This memcg can be obsolete one. We avoid calling css_tryget
+		 * We uncharge this because swap is freed.  This memcg can
+		 * be obsolete one. We avoid calling css_tryget_online().
 		 */
 		if (!mem_cgroup_is_root(memcg))
 			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
@@ -4711,18 +4709,28 @@
 	} while (usage > 0);
 }
 
+/*
+ * Test whether @memcg has children, dead or alive.  Note that this
+ * function doesn't care whether @memcg has use_hierarchy enabled and
+ * returns %true if there are child csses according to the cgroup
+ * hierarchy.  Testing use_hierarchy is the caller's responsiblity.
+ */
 static inline bool memcg_has_children(struct mem_cgroup *memcg)
 {
-	lockdep_assert_held(&memcg_create_mutex);
+	bool ret;
+
 	/*
-	 * The lock does not prevent addition or deletion to the list
-	 * of children, but it prevents a new child from being
-	 * initialized based on this parent in css_online(), so it's
-	 * enough to decide whether hierarchically inherited
-	 * attributes can still be changed or not.
+	 * The lock does not prevent addition or deletion of children, but
+	 * it prevents a new child from being initialized based on this
+	 * parent in css_online(), so it's enough to decide whether
+	 * hierarchically inherited attributes can still be changed or not.
 	 */
-	return memcg->use_hierarchy &&
-		!list_empty(&memcg->css.cgroup->children);
+	lockdep_assert_held(&memcg_create_mutex);
+
+	rcu_read_lock();
+	ret = css_next_child(NULL, &memcg->css);
+	rcu_read_unlock();
+	return ret;
 }
 
 /*
@@ -4734,11 +4742,6 @@
 static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
 {
 	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
-	struct cgroup *cgrp = memcg->css.cgroup;
-
-	/* returns EBUSY if there is a task or if we come here twice. */
-	if (cgroup_has_tasks(cgrp) || !list_empty(&cgrp->children))
-		return -EBUSY;
 
 	/* we call try-to-free pages for make this cgroup empty */
 	lru_add_drain_all();
@@ -4758,20 +4761,19 @@
 		}
 
 	}
-	lru_add_drain();
-	mem_cgroup_reparent_charges(memcg);
 
 	return 0;
 }
 
-static int mem_cgroup_force_empty_write(struct cgroup_subsys_state *css,
-					unsigned int event)
+static ssize_t mem_cgroup_force_empty_write(struct kernfs_open_file *of,
+					    char *buf, size_t nbytes,
+					    loff_t off)
 {
-	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
 
 	if (mem_cgroup_is_root(memcg))
 		return -EINVAL;
-	return mem_cgroup_force_empty(memcg);
+	return mem_cgroup_force_empty(memcg) ?: nbytes;
 }
 
 static u64 mem_cgroup_hierarchy_read(struct cgroup_subsys_state *css,
@@ -4785,7 +4787,7 @@
 {
 	int retval = 0;
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
-	struct mem_cgroup *parent_memcg = mem_cgroup_from_css(css_parent(&memcg->css));
+	struct mem_cgroup *parent_memcg = mem_cgroup_from_css(memcg->css.parent);
 
 	mutex_lock(&memcg_create_mutex);
 
@@ -4802,7 +4804,7 @@
 	 */
 	if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
 				(val == 1 || val == 0)) {
-		if (list_empty(&memcg->css.cgroup->children))
+		if (!memcg_has_children(memcg))
 			memcg->use_hierarchy = val;
 		else
 			retval = -EBUSY;
@@ -4919,7 +4921,8 @@
 	 * of course permitted.
 	 */
 	mutex_lock(&memcg_create_mutex);
-	if (cgroup_has_tasks(memcg->css.cgroup) || memcg_has_children(memcg))
+	if (cgroup_has_tasks(memcg->css.cgroup) ||
+	    (memcg->use_hierarchy && memcg_has_children(memcg)))
 		err = -EBUSY;
 	mutex_unlock(&memcg_create_mutex);
 	if (err)
@@ -5021,17 +5024,18 @@
  * The user of this function is...
  * RES_LIMIT.
  */
-static int mem_cgroup_write(struct cgroup_subsys_state *css, struct cftype *cft,
-			    char *buffer)
+static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
+				char *buf, size_t nbytes, loff_t off)
 {
-	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
 	enum res_type type;
 	int name;
 	unsigned long long val;
 	int ret;
 
-	type = MEMFILE_TYPE(cft->private);
-	name = MEMFILE_ATTR(cft->private);
+	buf = strstrip(buf);
+	type = MEMFILE_TYPE(of_cft(of)->private);
+	name = MEMFILE_ATTR(of_cft(of)->private);
 
 	switch (name) {
 	case RES_LIMIT:
@@ -5040,7 +5044,7 @@
 			break;
 		}
 		/* This function does all necessary parse...reuse it */
-		ret = res_counter_memparse_write_strategy(buffer, &val);
+		ret = res_counter_memparse_write_strategy(buf, &val);
 		if (ret)
 			break;
 		if (type == _MEM)
@@ -5053,7 +5057,7 @@
 			return -EINVAL;
 		break;
 	case RES_SOFT_LIMIT:
-		ret = res_counter_memparse_write_strategy(buffer, &val);
+		ret = res_counter_memparse_write_strategy(buf, &val);
 		if (ret)
 			break;
 		/*
@@ -5070,7 +5074,7 @@
 		ret = -EINVAL; /* should be BUG() ? */
 		break;
 	}
-	return ret;
+	return ret ?: nbytes;
 }
 
 static void memcg_get_hierarchical_limit(struct mem_cgroup *memcg,
@@ -5083,8 +5087,8 @@
 	if (!memcg->use_hierarchy)
 		goto out;
 
-	while (css_parent(&memcg->css)) {
-		memcg = mem_cgroup_from_css(css_parent(&memcg->css));
+	while (memcg->css.parent) {
+		memcg = mem_cgroup_from_css(memcg->css.parent);
 		if (!memcg->use_hierarchy)
 			break;
 		tmp = res_counter_read_u64(&memcg->res, RES_LIMIT);
@@ -5097,14 +5101,15 @@
 	*memsw_limit = min_memsw_limit;
 }
 
-static int mem_cgroup_reset(struct cgroup_subsys_state *css, unsigned int event)
+static ssize_t mem_cgroup_reset(struct kernfs_open_file *of, char *buf,
+				size_t nbytes, loff_t off)
 {
-	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
 	int name;
 	enum res_type type;
 
-	type = MEMFILE_TYPE(event);
-	name = MEMFILE_ATTR(event);
+	type = MEMFILE_TYPE(of_cft(of)->private);
+	name = MEMFILE_ATTR(of_cft(of)->private);
 
 	switch (name) {
 	case RES_MAX_USAGE:
@@ -5129,7 +5134,7 @@
 		break;
 	}
 
-	return 0;
+	return nbytes;
 }
 
 static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
@@ -5322,7 +5327,7 @@
 	if (val > 100)
 		return -EINVAL;
 
-	if (css_parent(css))
+	if (css->parent)
 		memcg->swappiness = val;
 	else
 		vm_swappiness = val;
@@ -5659,7 +5664,7 @@
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 
 	/* cannot set to root cgroup and only 0 and 1 are allowed */
-	if (!css_parent(css) || !((val == 0) || (val == 1)))
+	if (!css->parent || !((val == 0) || (val == 1)))
 		return -EINVAL;
 
 	memcg->oom_kill_disable = val;
@@ -5705,10 +5710,10 @@
 	 * which is then paired with css_put during uncharge resp. here.
 	 *
 	 * Although this might sound strange as this path is called from
-	 * css_offline() when the referencemight have dropped down to 0
-	 * and shouldn't be incremented anymore (css_tryget would fail)
-	 * we do not have other options because of the kmem allocations
-	 * lifetime.
+	 * css_offline() when the referencemight have dropped down to 0 and
+	 * shouldn't be incremented anymore (css_tryget_online() would
+	 * fail) we do not have other options because of the kmem
+	 * allocations lifetime.
 	 */
 	css_get(&memcg->css);
 
@@ -5827,9 +5832,10 @@
  * Input must be in format '<event_fd> <control_fd> <args>'.
  * Interpretation of args is defined by control file implementation.
  */
-static int memcg_write_event_control(struct cgroup_subsys_state *css,
-				     struct cftype *cft, char *buffer)
+static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
+					 char *buf, size_t nbytes, loff_t off)
 {
+	struct cgroup_subsys_state *css = of_css(of);
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 	struct mem_cgroup_event *event;
 	struct cgroup_subsys_state *cfile_css;
@@ -5840,15 +5846,17 @@
 	char *endp;
 	int ret;
 
-	efd = simple_strtoul(buffer, &endp, 10);
+	buf = strstrip(buf);
+
+	efd = simple_strtoul(buf, &endp, 10);
 	if (*endp != ' ')
 		return -EINVAL;
-	buffer = endp + 1;
+	buf = endp + 1;
 
-	cfd = simple_strtoul(buffer, &endp, 10);
+	cfd = simple_strtoul(buf, &endp, 10);
 	if ((*endp != ' ') && (*endp != '\0'))
 		return -EINVAL;
-	buffer = endp + 1;
+	buf = endp + 1;
 
 	event = kzalloc(sizeof(*event), GFP_KERNEL);
 	if (!event)
@@ -5916,8 +5924,8 @@
 	 * automatically removed on cgroup destruction but the removal is
 	 * asynchronous, so take an extra ref on @css.
 	 */
-	cfile_css = css_tryget_from_dir(cfile.file->f_dentry->d_parent,
-					&memory_cgrp_subsys);
+	cfile_css = css_tryget_online_from_dir(cfile.file->f_dentry->d_parent,
+					       &memory_cgrp_subsys);
 	ret = -EINVAL;
 	if (IS_ERR(cfile_css))
 		goto out_put_cfile;
@@ -5926,7 +5934,7 @@
 		goto out_put_cfile;
 	}
 
-	ret = event->register_event(memcg, event->eventfd, buffer);
+	ret = event->register_event(memcg, event->eventfd, buf);
 	if (ret)
 		goto out_put_css;
 
@@ -5939,7 +5947,7 @@
 	fdput(cfile);
 	fdput(efile);
 
-	return 0;
+	return nbytes;
 
 out_put_css:
 	css_put(css);
@@ -5964,25 +5972,25 @@
 	{
 		.name = "max_usage_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEM, RES_MAX_USAGE),
-		.trigger = mem_cgroup_reset,
+		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
 		.name = "limit_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEM, RES_LIMIT),
-		.write_string = mem_cgroup_write,
+		.write = mem_cgroup_write,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
 		.name = "soft_limit_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
-		.write_string = mem_cgroup_write,
+		.write = mem_cgroup_write,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
 		.name = "failcnt",
 		.private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
-		.trigger = mem_cgroup_reset,
+		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
@@ -5991,7 +5999,7 @@
 	},
 	{
 		.name = "force_empty",
-		.trigger = mem_cgroup_force_empty_write,
+		.write = mem_cgroup_force_empty_write,
 	},
 	{
 		.name = "use_hierarchy",
@@ -6001,7 +6009,7 @@
 	},
 	{
 		.name = "cgroup.event_control",		/* XXX: for compat */
-		.write_string = memcg_write_event_control,
+		.write = memcg_write_event_control,
 		.flags = CFTYPE_NO_PREFIX,
 		.mode = S_IWUGO,
 	},
@@ -6034,7 +6042,7 @@
 	{
 		.name = "kmem.limit_in_bytes",
 		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
-		.write_string = mem_cgroup_write,
+		.write = mem_cgroup_write,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
@@ -6045,13 +6053,13 @@
 	{
 		.name = "kmem.failcnt",
 		.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
-		.trigger = mem_cgroup_reset,
+		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
 		.name = "kmem.max_usage_in_bytes",
 		.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
-		.trigger = mem_cgroup_reset,
+		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 #ifdef CONFIG_SLABINFO
@@ -6074,19 +6082,19 @@
 	{
 		.name = "memsw.max_usage_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEMSWAP, RES_MAX_USAGE),
-		.trigger = mem_cgroup_reset,
+		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
 		.name = "memsw.limit_in_bytes",
 		.private = MEMFILE_PRIVATE(_MEMSWAP, RES_LIMIT),
-		.write_string = mem_cgroup_write,
+		.write = mem_cgroup_write,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{
 		.name = "memsw.failcnt",
 		.private = MEMFILE_PRIVATE(_MEMSWAP, RES_FAILCNT),
-		.trigger = mem_cgroup_reset,
+		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
 	{ },	/* terminate */
@@ -6264,9 +6272,9 @@
 mem_cgroup_css_online(struct cgroup_subsys_state *css)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
-	struct mem_cgroup *parent = mem_cgroup_from_css(css_parent(css));
+	struct mem_cgroup *parent = mem_cgroup_from_css(css->parent);
 
-	if (css->cgroup->id > MEM_CGROUP_ID_MAX)
+	if (css->id > MEM_CGROUP_ID_MAX)
 		return -ENOSPC;
 
 	if (!parent)
@@ -6361,7 +6369,7 @@
 	/*
 	 * XXX: css_offline() would be where we should reparent all
 	 * memory to prepare the cgroup for destruction.  However,
-	 * memcg does not do css_tryget() and res_counter charging
+	 * memcg does not do css_tryget_online() and res_counter charging
 	 * under the same RCU lock region, which means that charging
 	 * could race with offlining.  Offlining only happens to
 	 * cgroups with no tasks in them but charges can show up
@@ -6375,9 +6383,9 @@
 	 *                           lookup_swap_cgroup_id()
 	 *                           rcu_read_lock()
 	 *                           mem_cgroup_lookup()
-	 *                           css_tryget()
+	 *                           css_tryget_online()
 	 *                           rcu_read_unlock()
-	 * disable css_tryget()
+	 * disable css_tryget_online()
 	 * call_rcu()
 	 *   offline_css()
 	 *     reparent_charges()