linux-kernel - Re: [PATCH v2] block: flush all throttled bios when deleting the cgroup

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Date: Fri, 28 Jun 2024 10:04:20 +0800
From: Li Lingfeng <lilingfeng@...weicloud.com>
To: Tejun Heo <tj@...nel.org>
Cc: josef@...icpanda.com, hch@....de, axboe@...nel.dk, mkoutny@...e.com,
 cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yangerkun@...wei.com, yukuai1@...weicloud.com,
 houtao1@...wei.com, yi.zhang@...wei.com, lilingfeng3@...wei.com
Subject: Re: [PATCH v2] block: flush all throttled bios when deleting the
 cgroup


在 2024/6/28 4:43, Tejun Heo 写道:
> Hello, Li.
>
> On Thu, Jun 27, 2024 at 10:26:06PM +0800, Li Lingfeng wrote:
>> From: Li Lingfeng <lilingfeng3@...wei.com>
>>
>> When a process migrates to another cgroup and the original cgroup is deleted,
>> the restrictions of throttled bios cannot be removed. If the restrictions
>> are set too low, it will take a long time to complete these bios.
>>
>> Refer to the process of deleting a disk to remove the restrictions and
>> issue bios when deleting the cgroup.
>>
>> This makes difference on the behavior of throttled bios:
>> Before: the limit of the throttled bios can't be changed and the bios will
>> complete under this limit;
>> Now: the limit will be canceled and the throttled bios will be flushed
>> immediately.
> I'm not necessarily against this but the description doesn't explain why
> this is better either. Can you please detail why this behavior is better?
I think it may be more appropriate to remove the limit of bios after the
cgroup is deleted, rather than let the bios continue to be throttled by a
non-existent cgroup.

If the limit is set too low, and the original cgourp has been deleted, we
now have no way to make the bios complete immediately, but to wait for the
bios to slowly complete under the limit.

Thanks.

>
> Thanks.
>