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Date:   Fri, 18 Dec 2020 12:09:28 +1100
From:   Dave Chinner <>
To:     Yang Shi <>
Cc:     Roman Gushchin <>, Kirill Tkhai <>,
        Shakeel Butt <>,
        Johannes Weiner <>,
        Michal Hocko <>,
        Andrew Morton <>,
        Linux MM <>,
        Linux FS-devel Mailing List <>,
        Linux Kernel Mailing List <>
Subject: Re: [v2 PATCH 7/9] mm: vmscan: don't need allocate
 shrinker->nr_deferred for memcg aware shrinkers

On Thu, Dec 17, 2020 at 04:56:48PM -0800, Yang Shi wrote:
> On Tue, Dec 15, 2020 at 3:07 PM Yang Shi <> wrote:
> > > This guarantees that only the shrinker instances taht have a
> > > correctly set up memcg attached to them will have the
> > > SHRINKER_MEMCG_AWARE flag set. Hence in all the rest of the shrinker
> > > code, we only ever need to check for SHRINKER_MEMCG_AWARE to
> > > determine what we should do....
> >
> > Thanks. I see your point. We could move the memcg specific details
> > into prealloc_memcg_shrinker().
> >
> > It seems we have to acquire shrinker_rwsem before we check and modify
> > SHIRNKER_MEMCG_AWARE bit if we may clear it.
> Hi Dave,
> Is it possible that shrinker register races with shrinker unregister?
> It seems impossible to me by a quick visual code inspection. But I'm
> not a VFS expert so I'm not quite sure.

Uh, if you have a shrinker racing to register and unregister, you've
got a major bug in your object initialisation/teardown code. i.e.
calling reagister/unregister at the same time for the same shrinker
is a bug, pure and simple.


Dave Chinner

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