From: Pavel Emelyanov <xemul@openvz.org>

This field is the maximal value of the usage one since the counter creation
(or since the latest reset).

To reset this to the usage value simply write anything to the appropriate
cgroup file.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/res_counter.h |   14 ++++++++++++++
 kernel/res_counter.c        |    4 ++++
 mm/memcontrol.c             |   17 +++++++++++++++++
 3 files changed, 35 insertions(+)

diff -puN include/linux/res_counter.h~memcgroup-add-the-max_usage-member-on-the-res_counter include/linux/res_counter.h
--- a/include/linux/res_counter.h~memcgroup-add-the-max_usage-member-on-the-res_counter
+++ a/include/linux/res_counter.h
@@ -25,6 +25,10 @@ struct res_counter {
 	 */
 	unsigned long long usage;
 	/*
+	 * the maximal value of the usage from the counter creation
+	 */
+	unsigned long long max_usage;
+	/*
 	 * the limit that usage cannot exceed
 	 */
 	unsigned long long limit;
@@ -67,6 +71,7 @@ ssize_t res_counter_write(struct res_cou
 
 enum {
 	RES_USAGE,
+	RES_MAX_USAGE,
 	RES_LIMIT,
 	RES_FAILCNT,
 };
@@ -127,4 +132,13 @@ static inline bool res_counter_check_und
 	return ret;
 }
 
+static inline void res_counter_reset_max(struct res_counter *cnt)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cnt->lock, flags);
+	cnt->max_usage = cnt->usage;
+	spin_unlock_irqrestore(&cnt->lock, flags);
+}
+
 #endif
diff -puN kernel/res_counter.c~memcgroup-add-the-max_usage-member-on-the-res_counter kernel/res_counter.c
--- a/kernel/res_counter.c~memcgroup-add-the-max_usage-member-on-the-res_counter
+++ a/kernel/res_counter.c
@@ -28,6 +28,8 @@ int res_counter_charge_locked(struct res
 	}
 
 	counter->usage += val;
+	if (counter->usage > counter->max_usage)
+		counter->max_usage = counter->usage;
 	return 0;
 }
 
@@ -66,6 +68,8 @@ res_counter_member(struct res_counter *c
 	switch (member) {
 	case RES_USAGE:
 		return &counter->usage;
+	case RES_MAX_USAGE:
+		return &counter->max_usage;
 	case RES_LIMIT:
 		return &counter->limit;
 	case RES_FAILCNT:
diff -puN mm/memcontrol.c~memcgroup-add-the-max_usage-member-on-the-res_counter mm/memcontrol.c
--- a/mm/memcontrol.c~memcgroup-add-the-max_usage-member-on-the-res_counter
+++ a/mm/memcontrol.c
@@ -868,6 +868,17 @@ static ssize_t mem_cgroup_write(struct c
 				mem_cgroup_write_strategy);
 }
 
+static ssize_t mem_cgroup_max_reset(struct cgroup *cont, struct cftype *cft,
+				struct file *file, const char __user *userbuf,
+				size_t nbytes, loff_t *ppos)
+{
+	struct mem_cgroup *mem;
+
+	mem = mem_cgroup_from_cont(cont);
+	res_counter_reset_max(&mem->res);
+	return nbytes;
+}
+
 static ssize_t mem_force_empty_write(struct cgroup *cont,
 				struct cftype *cft, struct file *file,
 				const char __user *userbuf,
@@ -923,6 +934,12 @@ static struct cftype mem_cgroup_files[] 
 		.read_u64 = mem_cgroup_read,
 	},
 	{
+		.name = "max_usage_in_bytes",
+		.private = RES_MAX_USAGE,
+		.write = mem_cgroup_max_reset,
+		.read_u64 = mem_cgroup_read,
+	},
+	{
 		.name = "limit_in_bytes",
 		.private = RES_LIMIT,
 		.write = mem_cgroup_write,
_