[patch 040/127] mm,oom_reaper: do not attempt to reap a task twice

[patch 040/127] mm,oom_reaper: do not attempt to reap a task twice

[akpm]

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: mm,oom_reaper: do not attempt to reap a task twice

"mm, oom_reaper: do not attempt to reap a task twice" tried to give the
OOM reaper one more chance to retry using MMF_OOM_NOT_REAPABLE flag.  But
the usefulness of the flag is rather limited and actually never shown in
practice.  If the flag is set, it means that the holder of mm->mmap_sem
cannot call up_write() due to presumably being blocked at unkillable wait
waiting for other thread's memory allocation.  But since one of threads
sharing that mm will queue that mm immediately via task_will_free_mem()
shortcut (otherwise, oom_badness() will select the same mm again due to
oom_score_adj value unchanged), retrying MMF_OOM_NOT_REAPABLE mm is
unlikely helpful.

Let's always set MMF_OOM_REAPED.

Link: http://lkml.kernel.org/r/1472119394-11342-3-git-send-email-mhocko@kernel.org
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/sched.h |    1 -
 mm/oom_kill.c         |   15 +++------------
 2 files changed, 3 insertions(+), 13 deletions(-)

diff -puN include/linux/sched.h~mmoom_reaper-do-not-attempt-to-reap-a-task-twice include/linux/sched.h
--- a/include/linux/sched.h~mmoom_reaper-do-not-attempt-to-reap-a-task-twice
+++ a/include/linux/sched.h
@@ -525,7 +525,6 @@ static inline int get_dumpable(struct mm
 #define MMF_HAS_UPROBES		19	/* has uprobes */
 #define MMF_RECALC_UPROBES	20	/* MMF_HAS_UPROBES can be wrong */
 #define MMF_OOM_REAPED		21	/* mm has been already reaped */
-#define MMF_OOM_NOT_REAPABLE	22	/* mm couldn't be reaped */
 
 #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)
 
diff -puN mm/oom_kill.c~mmoom_reaper-do-not-attempt-to-reap-a-task-twice mm/oom_kill.c
--- a/mm/oom_kill.c~mmoom_reaper-do-not-attempt-to-reap-a-task-twice
+++ a/mm/oom_kill.c
@@ -578,20 +578,11 @@ static void oom_reap_task(struct task_st
 	if (attempts <= MAX_OOM_REAP_RETRIES)
 		goto done;
 
+	/* Ignore this mm because somebody can't call up_write(mmap_sem). */
+	set_bit(MMF_OOM_REAPED, &mm->flags);
+
 	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
 		task_pid_nr(tsk), tsk->comm);