On Thu 04-02-16 23:22:18, Tetsuo Handa wrote:

Michal Hocko wrote:

quoted

From: Michal Hocko <mhocko@suse.com>

When oom_reaper manages to unmap all the eligible vmas there shouldn't
be much of the freable memory held by the oom victim left anymore so it
makes sense to clear the TIF_MEMDIE flag for the victim and allow the
OOM killer to select another task.

Just a confirmation. Is it safe to clear TIF_MEMDIE without reaching do_exit()
with regard to freezing_slow_path()? Since clearing TIF_MEMDIE from the OOM
reaper confuses

    wait_event(oom_victims_wait, !atomic_read(&oom_victims));

in oom_killer_disable(), I'm worrying that the freezing operation continues
before the OOM victim which escaped the __refrigerator() actually releases
memory. Does this cause consistency problem?

This is a good question! At first sight it seems this is not safe and we
might need to make the oom_reaper freezable so that it doesn't wake up
during suspend and interfere. Let me think about that.

quoted

+	/*
+	 * Clear TIF_MEMDIE because the task shouldn't be sitting on a
+	 * reasonably reclaimable memory anymore. OOM killer can continue
+	 * by selecting other victim if unmapping hasn't led to any
+	 * improvements. This also means that selecting this task doesn't
+	 * make any sense.
+	 */
+	tsk->signal->oom_score_adj = OOM_SCORE_ADJ_MIN;
+	exit_oom_victim(tsk);

I noticed that updating only one thread group's oom_score_adj disables
further wake_oom_reaper() calls due to rough-grained can_oom_reap check at

  p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN

in oom_kill_process(). I think we need to either update all thread groups'
oom_score_adj using the reaped mm equally or use more fine-grained can_oom_reap
check which ignores OOM_SCORE_ADJ_MIN if all threads in that thread group are
dying or exiting.

I do not understand. Why would you want to reap the mm again when
this has been done already? The mm is shared, right?
-- 
Michal Hocko
SUSE Labs

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