[PATCH 7/9] oom: make oom_reaper_list single linked

[Michal Hocko]

From: Vladimir Davydov <vdavy...@virtuozzo.com>

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 <vdavy...@virtuozzo.com>
Acked-by: Michal Hocko <mho...@suse.com>
---
 include/linux/sched.h |  2 +-
 mm/oom_kill.c         | 15 +++++++--------
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index acb480b581e3..d118445a332e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1841,7 +1841,7 @@ struct task_struct {
 #endif
        int pagefault_disabled;
 #ifdef CONFIG_MMU
-       struct list_head oom_reaper_list;
+       struct task_struct *oom_reaper_list;
 #endif
 /* CPU-specific state of this task */
        struct thread_struct thread;
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index b38a648558f9..af75260f32c3 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -417,7 +417,7 @@ 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);
 
 
@@ -527,13 +527,11 @@ 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);
 
@@ -552,7 +550,8 @@ 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);
 }
-- 
2.7.0