linux-kernel - Re: [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while killing a process

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Date:   Fri, 13 Nov 2020 15:55:39 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     mhocko@...nel.org, rientjes@...gle.com, willy@...radead.org,
        hannes@...xchg.org, guro@...com, riel@...riel.com,
        minchan@...nel.org, christian@...uner.io, oleg@...hat.com,
        timmurray@...gle.com, linux-api@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while
 killing a process

On Fri, 13 Nov 2020 09:34:48 -0800 Suren Baghdasaryan <surenb@...gle.com> wrote:

> When a process is being killed it might be in an uninterruptible sleep
> which leads to an unpredictable delay in its memory reclaim. In low memory
> situations, when it's important to free up memory quickly, such delay is
> problematic. Kernel solves this problem with oom-reaper thread which
> performs memory reclaim even when the victim process is not runnable.
> Userspace currently lacks such mechanisms and the need and potential
> solutions were discussed before (see links below).
> This patch provides a mechanism to perform memory reclaim in the context
> of the process that sends SIGKILL signal. New SYNC_REAP_MM flag for
> pidfd_send_signal syscall can be used only when sending SIGKILL signal
> and will lead to the caller synchronously reclaiming the memory that
> belongs to the victim and can be easily reclaimed.

hm.

Seems to me that the ability to reap another process's memory is a
generally useful one, and that it should not be tied to delivering a
signal in this fashion.

And we do have the new process_madvise(MADV_PAGEOUT).  It may need a
few changes and tweaks, but can't that be used to solve this problem?