linux-kernel - Re: [patch] mm, oom: prevent additional oom kills before memory is freed

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Message-Id: <201706160400.v5G40ADv033862@www262.sakura.ne.jp>
Date:   Fri, 16 Jun 2017 13:00:10 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [patch] mm, oom: prevent additional oom kills before memory is freed

Tetsuo Handa wrote:
> and clarify in your patch that there is no possibility
> of waiting for direct/indirect memory allocation inside free_pgtables(),
> in addition to fixing the bug above.

Oops, this part was wrong, for __oom_reap_task_mm() will give up after
waiting for one second because down_read_trylock(&mm->mmap_sem) continues
failing due to down_write(&mm->mmap_sem) by exit_mmap().
# This is after all moving the location of "give up by timeout", isn't it? ;-)

Thus, clarify in your patch that there is no possibility of waiting for
direct/indirect memory allocation outside down_write()/up_write() (e.g.
i_mmap_lock_write() inside unmap_vmas(&tlb, vma, 0, -1) just before
down_write()).