Re: [PATCH] memcg, thp: do not invoke oom killer on thp charges

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Mar 21, 2018 at 09:59:28PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> David has noticed that THP memcg charge can trigger the oom killer
> since 2516035499b9 ("mm, thp: remove __GFP_NORETRY from khugepaged and
> madvised allocations"). We have used an explicit __GFP_NORETRY
> previously which ruled the OOM killer automagically.
> 
> Memcg charge path should be semantically compliant with the allocation
> path and that means that if we do not trigger the OOM killer for costly
> orders which should do the same in the memcg charge path as well.
> Otherwise we are forcing callers to distinguish the two and use
> different gfp masks which is both non-intuitive and bug prone. Not to
> mention the maintenance burden.
> 
> Teach mem_cgroup_oom to bail out on costly order requests to fix the THP
> issue as well as any other costly OOM eligible allocations to be added
> in future.
> 
> Fixes: 2516035499b9 ("mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations")
> Reported-by: David Rientjes <rientjes@google.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

I also prefer this fix over having separate OOM behaviors (which is
user-visible, and not just about technical ability to satisfy the
allocation) between the allocator and memcg.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>