linux-kernel - Re: [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing

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Message-ID: <20190821160430.GL2263813@devbig004.ftw2.facebook.com>
Date:   Wed, 21 Aug 2019 09:04:30 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Jan Kara <jack@...e.cz>
Cc:     axboe@...nel.dk, hannes@...xchg.org, mhocko@...nel.org,
        vdavydov.dev@...il.com, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, guro@...com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH 5/5] writeback, memcg: Implement foreign dirty flushing

On Wed, Aug 21, 2019 at 09:00:37AM -0700, Tejun Heo wrote:
> > 2) When you invalidate frn entry here by writing 0 to 'at', it's likely to get
> > reused soon. Possibly while the writeback is still running. And then you
> > won't start any writeback for the new entry because of the
> > atomic_read(&frn->done.cnt) == 1 check. This seems like it could happen
> > pretty frequently?
> 
> Hmm... yeah, the clearing might not make sense.  I'll remove that.

Oh, the reuse logic checks whether done.cnt == 1 and only reuse if no
writeback is still in flight, so this one should be fine.

Thanks.

-- 
tejun