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>

1 files changed, 7 insertions, 8 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1a21819a8e5e..a49638f41e45 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -419,7 +419,7 @@ bool oom_killer_disabled __read_mostly;
  */
 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 @@ static int oom_reaper(void *unused)
         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 @@ static void wake_oom_reaper(struct task_struct *tsk)
         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);
 }