linux-kernel - Re: [PATCH v5] mm: vmpressure: don't count proactive reclaim in vmpressure

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Message-ID: <539ddf30-160b-848d-5249-770963cba5ab@google.com>
Date:   Thu, 28 Jul 2022 14:45:24 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Miaohe Lin <linmiaohe@...wei.com>, NeilBrown <neilb@...e.de>,
        Alistair Popple <apopple@...dia.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5] mm: vmpressure: don't count proactive reclaim in
 vmpressure

On Thu, 21 Jul 2022, Yosry Ahmed wrote:

> memory.reclaim is a cgroup v2 interface that allows users to
> proactively reclaim memory from a memcg, without real memory pressure.
> Reclaim operations invoke vmpressure, which is used:
> (a) To notify userspace of reclaim efficiency in cgroup v1, and
> (b) As a signal for a memcg being under memory pressure for networking
> (see mem_cgroup_under_socket_pressure()).
> 
> For (a), vmpressure notifications in v1 are not affected by this change
> since memory.reclaim is a v2 feature.
> 
> For (b), the effects of the vmpressure signal (according to Shakeel [1])
> are as follows:
> 1. Reducing send and receive buffers of the current socket.
> 2. May drop packets on the rx path.
> 3. May throttle current thread on the tx path.
> 
> Since proactive reclaim is invoked directly by userspace, not by
> memory pressure, it makes sense not to throttle networking. Hence,
> this change makes sure that proactive reclaim caused by memory.reclaim
> does not trigger vmpressure.
> 
> [1] https://lore.kernel.org/lkml/CALvZod68WdrXEmBpOkadhB5GPYmCXaDZzXH=yyGOCAjFRn4NDQ@mail.gmail.com/
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

Acked-by: David Rientjes <rientjes@...gle.com>