linux-kernel - Re: [PATCH] mm: memcontrol: don't count limit-setting reclaim as memory pressure

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Date:   Tue, 28 Jul 2020 08:03:56 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH] mm: memcontrol: don't count limit-setting reclaim as
 memory pressure

On Tue, Jul 28, 2020 at 6:53 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> When an outside process lowers one of the memory limits of a cgroup
> (or uses the force_empty knob in cgroup1), direct reclaim is performed
> in the context of the write(), in order to directly enforce the new
> limit and have it being met by the time the write() returns.
>
> Currently, this reclaim activity is accounted as memory pressure in
> the cgroup that the writer(!) belongs to. This is unexpected.

Indeed this is unexpected.

> It
> specifically causes problems for senpai
> (https://github.com/facebookincubator/senpai), which is an agent that
> routinely adjusts the memory limits and performs associated reclaim
> work in tens or even hundreds of cgroups running on the host. The
> cgroup that senpai is running in itself will report elevated levels of
> memory pressure, even though it itself is under no memory shortage or
> any sort of distress.
>
> Move the psi annotation from the central cgroup reclaim function to
> callsites in the allocation context, and thereby no longer count any
> limit-setting reclaim as memory pressure. If the newly set limit
> causes the workload inside the cgroup into direct reclaim, that of
> course will continue to count as memory pressure.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>