commit 29c696e1c6eceb5db6b21f0c89495fcfcd40c0eb
author Vladimir Davydov <vdavydov@virtuozzo.com> Fri Mar 25 14:20:39 2016 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Fri Mar 25 16:37:42 2016 -0700
tree fe5a096de3c34d3fef0fcc40dd3fbc03a99599a1
parent 855b018325737f7691f9b7d86339df40aa4e47c3

oom: make oom_reaper_list single linked

Entries are only added/removed from oom_reaper_list at head so we can
use a single linked list and hence save a word in task_struct.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1a21819..a49638f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -419,7 +419,7 @@
  */
 static struct task_struct *oom_reaper_th;
 static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
-static LIST_HEAD(oom_reaper_list);
+static struct task_struct *oom_reaper_list;
 static DEFINE_SPINLOCK(oom_reaper_lock);
 
 
@@ -528,13 +528,11 @@
 	while (true) {
 		struct task_struct *tsk = NULL;
 
-		wait_event_freezable(oom_reaper_wait,
-				     (!list_empty(&oom_reaper_list)));
+		wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
 		spin_lock(&oom_reaper_lock);
-		if (!list_empty(&oom_reaper_list)) {
-			tsk = list_first_entry(&oom_reaper_list,
-					struct task_struct, oom_reaper_list);
-			list_del(&tsk->oom_reaper_list);
+		if (oom_reaper_list != NULL) {
+			tsk = oom_reaper_list;
+			oom_reaper_list = tsk->oom_reaper_list;
 		}
 		spin_unlock(&oom_reaper_lock);
 
@@ -553,7 +551,8 @@
 	get_task_struct(tsk);
 
 	spin_lock(&oom_reaper_lock);
-	list_add(&tsk->oom_reaper_list, &oom_reaper_list);
+	tsk->oom_reaper_list = oom_reaper_list;
+	oom_reaper_list = tsk;
 	spin_unlock(&oom_reaper_lock);
 	wake_up(&oom_reaper_wait);
 }