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Date:   Tue, 12 Jan 2021 14:53:06 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>,
        Michal Hocko <mhocko@...e.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: prevent starvation when writing
 memory.high

On Tue, Jan 12, 2021 at 10:59:58AM -0800, Shakeel Butt wrote:
> On Tue, Jan 12, 2021 at 9:12 AM Johannes Weiner <hannes@...xchg.org> wrote:
> >
> > When a value is written to a cgroup's memory.high control file, the
> > write() context first tries to reclaim the cgroup to size before
> > putting the limit in place for the workload. Concurrent charges from
> > the workload can keep such a write() looping in reclaim indefinitely.
> >
> 
> Is this observed on real workload?

Yes.

On several production hosts running a particularly aggressive
workload, we've observed writers to memory.high getting stuck for
minutes while consuming significant amount of CPU.

> Any particular reason to remove !reclaimed?

It's purpose so far was to allow successful reclaim to continue
indefinitely, while restricting no-progress loops to 'nr_retries'.

Without the first part, it doesn't really matter whether reclaim is
making progress or not: we do a maximum of 'nr_retries' loops until
the cgroup size meets the new limit, then exit one way or another.

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