linux-kernel - [v3 1/6] mm, oom: use oom_victims counter to synchronize oom victim selection

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Date:   Wed, 21 Jun 2017 22:19:11 +0100
From:   Roman Gushchin <guro@...com>
To:     <linux-mm@...ck.org>
CC:     Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        <kernel-team@...com>, <cgroups@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [v3 1/6] mm, oom: use oom_victims counter to synchronize oom victim selection

Oom killer should avoid unnecessary kills. To prevent them, during
the tasks list traverse we check for task which was previously
selected as oom victims. If there is such a task, new victim
is not selected.

This approach is sub-optimal (we're doing costly iteration over the task
list every time) and will not work for the cgroup-aware oom killer.

We already have oom_victims counter, which can be effectively used
for the task.

If there are victims in flight, don't do anything; if the counter
falls to 0, there are no more oom victims left.
So, it's a good time to start looking for a new victim.

Signed-off-by: Roman Gushchin <guro@...com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: kernel-team@...com
Cc: cgroups@...r.kernel.org
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
---
 mm/oom_kill.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 0e2c925..e3aaf5c8 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -992,6 +992,13 @@ bool out_of_memory(struct oom_control *oc)
 	if (oom_killer_disabled)
 		return false;
 
+	/*
+	 * If there are oom victims in flight, we don't need to select
+	 * a new victim.
+	 */
+	if (atomic_read(&oom_victims) > 0)
+		return true;
+
 	if (!is_memcg_oom(oc)) {
 		blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
 		if (freed > 0)
-- 
2.7.4