linux-kernel - Re: [PATCH v2 1/2] mm: drop oom code from exit

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Date:   Mon, 16 May 2022 21:12:14 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc:     mhocko@...e.com, rientjes@...gle.com, willy@...radead.org,
        hannes@...xchg.org, guro@...com, minchan@...nel.org,
        kirill@...temov.name, aarcange@...hat.com, brauner@...nel.org,
        hch@...radead.org, oleg@...hat.com, david@...hat.com,
        jannh@...gle.com, shakeelb@...gle.com, peterx@...hat.com,
        jhubbard@...dia.com, shuah@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-team@...roid.com, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2 1/2] mm: drop oom code from exit_mmap

On 5/16/22 1:56 AM, Suren Baghdasaryan wrote:
> The primary reason to invoke the oom reaper from the exit_mmap path used
> to be a prevention of an excessive oom killing if the oom victim exit
> races with the oom reaper (see [1] for more details). The invocation has
> moved around since then because of the interaction with the munlock
> logic but the underlying reason has remained the same (see [2]).
> 
> Munlock code is no longer a problem since [3] and there shouldn't be
> any blocking operation before the memory is unmapped by exit_mmap so
> the oom reaper invocation can be dropped. The unmapping part can be done
> with the non-exclusive mmap_sem and the exclusive one is only required
> when page tables are freed.
> 
> Remove the oom_reaper from exit_mmap which will make the code easier to
> read. This is really unlikely to make any observable difference although
> some microbenchmarks could benefit from one less branch that needs to be
> evaluated even though it almost never is true.
> 
> [1] 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
> [2] 27ae357fa82b ("mm, oom: fix concurrent munlock and oom reaper unmap, v3")
> [3] a213e5cf71cb ("mm/munlock: delete munlock_vma_pages_all(), allow oomreap")
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> ---
Looks good to me.

Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>

thanks,
-- Shuah