On Thu 04-02-16 15:43:19, Michal Hocko wrote:

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

quoted

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.

OK, I was thinking about it some more and it seems you are right here.
oom_reaper as a kernel thread is not freezable automatically and so it
might interfere after all the processes/kernel threads are considered
frozen. Then it really might shut down TIF_MEMDIE too early and wake out
oom_killer_disable. wait_event_freezable is not sufficient because the
oom_reaper might running while the PM freezer is freezing tasks and it
will miss it because it doesn't see it.

So I think we might need this. I am heading to vacation today and will
be offline for the next week so I will prepare the full patch with the
proper changelog after I get back:

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ca61e6cfae52..7e9953a64489 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c

@@ -521,6 +521,8 @@ static void oom_reap_task(struct task_struct *tsk)
 
 static int oom_reaper(void *unused)
 {
+	set_freezable();
+
 	while (true) {
 		struct task_struct *tsk = NULL;
 

-- 
Michal Hocko
SUSE Labs

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