linux-kernel - Re: [PATCH -next] block, bfq: cleanup 'bfqg->online'

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Date:   Thu, 2 Feb 2023 09:16:52 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Jan Kara <jack@...e.cz>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
        paolo.valente@...aro.org, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next] block, bfq: cleanup 'bfqg->online'

Hi, Jan!

在 2023/02/01 21:10, Jan Kara 写道:
> On Wed 01-02-23 20:06:09, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> After commit dfd6200a0954 ("blk-cgroup: support to track if policy is
>> online"), there is no need to do this again in bfq.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> 
> So I agree this is nice to do but it isn't so simple. BFQ relies on the
> fact that 'online' is cleared under bfqd->lock so we cannot associate bio
> in bfq_bio_bfqg() with a bfqg that has already its bfq_pd_offline()
> function run.
> 
> Maybe if you set 'online' to false before calling ->pd_offline() things
> would work fine for BFQ.

Yes, you're right. Thanks for the explanation.

Kuai