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

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Date: Tue, 2 Jul 2024 16:25:13 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Li Lingfeng <lilingfeng@...weicloud.com>
Cc: Tejun Heo <tj@...nel.org>, josef@...icpanda.com, hch@....de, 
	axboe@...nel.dk, 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

On Fri, Jun 28, 2024 at 10:04:20AM GMT, Li Lingfeng <lilingfeng@...weicloud.com> wrote:
> 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.

I'm not that familiar with this part -- can this also happen for IOs
submitted by an exited task? (In contrast to a running task migrated
elsewhere.)

> 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.

It makes some sense, it's not unlike reparenting of memcg objects, IIRC
flushed bios would actually be passed to a parent throtl_grp, right?

Thanks,
Michal

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