[PATCH 3/3] mm,oom: Remove oom_lock serialization from the OOM reaper.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Since "mm,oom: Move last second allocation to inside the OOM killer."
changed to do last second allocation attempt after confirming that there
is no OOM victim's mm without MMF_OOM_SKIP set, we no longer need to
block the OOM reaper using oom_lock. This patch should allow start
reclaiming earlier than now.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 mm/oom_kill.c | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 348ec5a..3b0d0fe 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -491,22 +491,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 	struct vm_area_struct *vma;
 	bool ret = true;
 
-	/*
-	 * We have to make sure to not race with the victim exit path
-	 * and cause premature new oom victim selection:
-	 * __oom_reap_task_mm		exit_mm
-	 *   mmget_not_zero
-	 *				  mmput
-	 *				    atomic_dec_and_test
-	 *				  exit_oom_victim
-	 *				[...]
-	 *				out_of_memory
-	 *				  select_bad_process
-	 *				    # no TIF_MEMDIE task selects new victim
-	 *  unmap_page_range # frees some memory
-	 */
-	mutex_lock(&oom_lock);
-
 	if (!down_read_trylock(&mm->mmap_sem)) {
 		ret = false;
 		trace_skip_task_reaping(tsk->pid);
@@ -580,7 +564,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 
 	trace_finish_task_reaping(tsk->pid);
 unlock_oom:
-	mutex_unlock(&oom_lock);
 	return ret;
 }
 
-- 
1.8.3.1

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