linux-kernel - Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg

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Date:   Fri, 6 Jan 2023 09:08:45 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Tejun Heo <tj@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     hch@...radead.org, josef@...icpanda.com, axboe@...nel.dk,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg

Hi,

在 2023/01/06 2:32, Tejun Heo 写道:
> On Thu, Jan 05, 2023 at 09:14:07AM +0800, Yu Kuai wrote:
>> 1) is related to blkg, while 2) is not, hence refcnting from blkg can't
>> fix the problem. refcnting from blkcg_policy_data should be ok, but I
>> see that bfq already has the similar refcnting, while other policy
>> doesn't require such refcnting.
> 
> Hmm... taking a step back, wouldn't this be solved by moving the first part
> of ioc_pd_free() to pd_offline_fn()? The ordering is strictly defined there,
> right?
> 

Moving first part to pd_offline_fn() has some requirements, like what I
did in the other thread:

iocg can be activated again after pd_offline_fn(), which is possible
because bio can be dispatched when cgroup is removed. I tried to avoid
that by:

1) dispatch all throttled bio io ioc_pd_offline()
2) don't throttle bio after ioc_pd_offline()

However, you already disagreed with that. 😔

Thanks,
Kuai

> Thanks.
> 
> --
> tejun
> .
>