Messages in this thread | | | Date | Wed, 4 Dec 2013 15:51:57 -0800 (PST) | From | David Rientjes <> | Subject | Re: [patch 2/2] mm: memcg: do not allow task about to OOM kill to bypass the limit |
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On Wed, 4 Dec 2013, Johannes Weiner wrote:
> 4942642080ea ("mm: memcg: handle non-error OOM situations more > gracefully") allowed tasks that already entered a memcg OOM condition > to bypass the memcg limit on subsequent allocation attempts hoping > this would expedite finishing the page fault and executing the kill. > > David Rientjes is worried that this breaks memcg isolation guarantees > and since there is no evidence that the bypass actually speeds up > fault processing just change it so that these subsequent charge > attempts fail outright. The notable exception being __GFP_NOFAIL > charges which are required to bypass the limit regardless. > > Reported-by: David Rientjes <rientjes@google.com> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: David Rientjes <rientjes@google.com>
Thanks!
I think we should consider marking this for stable@vger.kernel.org for 3.12 since the original patch went into 3.12-rc6. Depending on the number of allocators in the oom memcg, the amount of memory bypassed can become quite large.
For example, in a memcg with a limit of 128MB, if you start 10 concurrent processes that simply allocate a lot of memory you can get quite a bit of memory bypassed. If I start 10 membench processes, which would cause a 128MB memcg to oom even if only one such process were running, we get:
# grep RSS /proc/1092[0-9]/status VmRSS: 15724 kB VmRSS: 15064 kB VmRSS: 13224 kB VmRSS: 14520 kB VmRSS: 14472 kB VmRSS: 13016 kB VmRSS: 13024 kB VmRSS: 14560 kB VmRSS: 14864 kB VmRSS: 14772 kB
And all of those total ~140MB of memory while bound to a memcg with a 128MB limit, about 10% of memory is bypassed.
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