linux-kernel - Re: [PATCH] sbitmap: fix possible io hung due to lost wakeup

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Message-ID: <Yxjg2Xsb7WExRv2w@kbusch-mbp.dhcp.thefacebook.com>
Date:   Wed, 7 Sep 2022 12:20:09 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Jan Kara <jack@...e.cz>
Cc:     Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk, osandov@...com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yi.zhang@...wei.com
Subject: Re: [PATCH] sbitmap: fix possible io hung due to lost wakeup

On Wed, Sep 07, 2022 at 06:41:50PM +0200, Jan Kara wrote:
> On Wed 07-09-22 08:13:40, Keith Busch wrote:
> > 
> > I'm not sure about this part. We've already decremented, so the freed bit is
> > accounted for against the batch. Returning true here may double-count the freed
> > bit, right?
> 
> Yes, we may wake up waiters unnecessarily frequently. But that's a
> performance issue at worst and only if it happens frequently. So I don't
> think it matters in practice (famous last words ;).

Ok, let's go with that. Do you want to send the patch? I have a follow-up fix
for batched tagging that depends on this.