On Tue 01-08-17 13:42:38, Roman Gushchin wrote:

On Tue, Aug 01, 2017 at 02:29:05PM +0200, Michal Hocko wrote:

quoted

On Tue 01-08-17 13:23:44, Roman Gushchin wrote:

quoted

On Tue, Aug 01, 2017 at 02:16:44PM +0200, Michal Hocko wrote:

quoted

On Thu 27-07-17 11:03:55, Michal Hocko wrote:

quoted

Hi,
this is a part of a larger series I posted back in Oct last year [1]. I
have dropped patch 3 because it was incorrect and patch 4 is not
applicable without it.

The primary reason to apply patch 1 is to remove a risk of the complete
memory depletion by oom victims. While this is a theoretical risk right
now there is a demand for memcg aware oom killer which might kill all
processes inside a memcg which can be a lot of tasks. That would make
the risk quite real.

This issue is addressed by limiting access to memory reserves. We no
longer use TIF_MEMDIE to grant the access and use tsk_is_oom_victim
instead. See Patch 1 for more details. Patch 2 is a trivial follow up
cleanup.

Any comments, concerns? Can we merge it?

I've rebased the cgroup-aware OOM killer and ran some tests.
Everything works well.

Thanks for your testing. Can I assume your Tested-by?

Sure.

Thanks!

I wonder if we can get rid of TIF_MEMDIE completely,
if we will count OOM victims on per-oom-victim-signal-struct rather than
on per-thread basis? Say, assign oom_mm using cmpxchg, and call
exit_oom_victim() from __exit_signal()? __thaw_task() can be called from
mark_oom_victim() unconditionally.

Do you see any problems with this approach?

Ohh, I wish we could do that. All my previous attempts failed though. I
have always hit the problem to tell that the last thread of the process
is exiting to know when to call exit_oom_victim and release the oom
disable barrier. Maybe things have changed somehow since I've tried the
last time but this is a tricky code. I will certainly get back to it
some day but not likely anytime soon.

-- 
Michal Hocko
SUSE Labs

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