linux-kernel - Re: [v2 PATCH 2/9] mm: memcontrol: use shrinker_rwsem to protect shrinker

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Message-ID: <CAHbLzkpVk3uHO+g=iQLavRJ1c96FuaKTKVz0pUUHSk1L2rJcfQ@mail.gmail.com>
Date:   Tue, 15 Dec 2020 12:32:52 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Roman Gushchin <guro@...com>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Dave Chinner <david@...morbit.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH 2/9] mm: memcontrol: use shrinker_rwsem to protect
 shrinker_maps allocation

On Tue, Dec 15, 2020 at 6:10 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Mon, Dec 14, 2020 at 02:37:15PM -0800, Yang Shi wrote:
> > Since memcg_shrinker_map_size just can be changd under holding shrinker_rwsem
> > exclusively, the read side can be protected by holding read lock, so it sounds
> > superfluous to have a dedicated mutex.  This should not exacerbate the contention
> > to shrinker_rwsem since just one read side critical section is added.
> >
> > Signed-off-by: Yang Shi <shy828301@...il.com>
>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
>
> Thanks Yang, this is a step in the right direction. It would still be
> nice to also drop memcg_shrinker_map_size and (trivially) derive that
> value from shrinker_nr_max where necessary. It is duplicate state.

Thanks! I will take a further look at it.