[4.2.y-ckt stable] Patch "mm: memcontrol: reclaim when shrinking memory.high below usage" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    mm: memcontrol: reclaim when shrinking memory.high below usage

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt7.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From fbba56fd42359c73d69f4c05ba41eeb836511258 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes at cmpxchg.org>
Date: Thu, 17 Mar 2016 14:20:25 -0700
Subject: mm: memcontrol: reclaim when shrinking memory.high below usage

commit 588083bb37a3cea8533c392370a554417c8f29cb upstream.

When setting memory.high below usage, nothing happens until the next
charge comes along, and then it will only reclaim its own charge and not
the now potentially huge excess of the new memory.high.  This can cause
groups to stay in excess of their memory.high indefinitely.

To fix that, when shrinking memory.high, kick off a reclaim cycle that
goes after the delta.

Signed-off-by: Johannes Weiner <hannes at cmpxchg.org>
Acked-by: Michal Hocko <mhocko at suse.com>
Cc: Vladimir Davydov <vdavydov at virtuozzo.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/memcontrol.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 48540e5..1021069 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5422,6 +5422,7 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
 				 char *buf, size_t nbytes, loff_t off)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+	unsigned long nr_pages;
 	unsigned long high;
 	int err;

@@ -5432,6 +5433,11 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,

 	memcg->high = high;

+	nr_pages = page_counter_read(&memcg->memory);
+	if (nr_pages > high)
+		try_to_free_mem_cgroup_pages(memcg, nr_pages - high,
+					     GFP_KERNEL, true);
+
 	memcg_wb_domain_size_changed(memcg);
 	return nbytes;
 }
--
2.7.4