Re: [PATCH] mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> > We don't need to give up task_will_free_mem(current) without trying
> > allocation from memory reserves. We will need to select next OOM victim
> > only when allocation from memory reserves did not help.
> > 
> > Thus, this patch allows task_will_free_mem(current) to ignore MMF_OOM_SKIP
> > for once so that task_will_free_mem(current) will not start selecting next
> > OOM victim without trying allocation from memory reserves.
> 
> As I've already said this is an ugly hack and once we have
> http://lkml.kernel.org/r/20170727090357.3205-2-mhocko@kernel.org merged
> then it even shouldn't be needed because _all_ threads of the oom victim
> will have an instant access to memory reserves.
> 
> So I do not think we want to merge this.
> 

No, we still want to merge this, for 4.8+ kernels which won't get your patch
backported will need this. Even after your patch is merged, there is a race
window where allocating threads are between after gfp_pfmemalloc_allowed() and
before mutex_trylock(&oom_lock) in __alloc_pages_may_oom() which means that
some threads could call out_of_memory() and hit this task_will_free_mem(current)
test. Ignoring MMF_OOM_SKIP for once is still useful.

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