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

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Message-ID: <20201215020957.GK3913616@dread.disaster.area>
Date:   Tue, 15 Dec 2020 13:09:57 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     guro@...com, ktkhai@...tuozzo.com, shakeelb@...gle.com,
        hannes@...xchg.org, mhocko@...e.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH 2/9] mm: memcontrol: use shrinker_rwsem to protect
 shrinker_maps allocation

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.

I'm not sure this is a good idea. This couples the shrinker
infrastructure to internal details of how cgroups are initialised
and managed. Sure, certain operations might be done in certain
shrinker lock contexts, but that doesn't mean we should share global
locks across otherwise independent subsystems....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com