linux-kernel - Re: [PATCH v3] block: flush all throttled bios when deleting the cgroup

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Message-ID: <028f4d78-ebf6-c9cf-a8d8-718779cbe419@huaweicloud.com>
Date: Tue, 20 Aug 2024 15:13:37 +0800
From: Li Lingfeng <lilingfeng@...weicloud.com>
To: Tejun Heo <tj@...nel.org>
Cc: josef@...icpanda.com, hch@....de, mkoutny@...e.com, axboe@...nel.dk,
 cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yukuai1@...weicloud.com, houtao1@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, yukuai3@...wei.com,
 lilingfeng3@...wei.com
Subject: Re: [PATCH v3] block: flush all throttled bios when deleting the
 cgroup


在 2024/8/20 5:24, Tejun Heo 写道:
> Hello,
>
> On Sat, Aug 17, 2024 at 03:11:08PM +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 still don't see why this behavior is better. Wouldn't this make it easy to
> escape IO limits by creating cgroups, doing a bunch of IOs and then deleting
> them?
>
> Thanks.
Yes, this actually would make it easy to escape IO limits.

As described by Yu Kuai in v2, I changed this to prevent IO hang.
And I think it may be more appropriate to remove the limits in this
scenario since the limits were set by cgroup and the cgroup has been
deleted.

Thanks.