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

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Message-ID: <k56cnz7q5hxzh6hqmw4gnxobr2wlo6xryf4jqlky3mylcs4px4@zrhciaca2asy>
Date: Tue, 20 Aug 2024 12:00:53 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Tejun Heo <tj@...nel.org>
Cc: Li Lingfeng <lilingfeng@...weicloud.com>, josef@...icpanda.com, 
	hch@....de, 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

On Mon, Aug 19, 2024 at 11:24:18AM GMT, Tejun Heo <tj@...nel.org> wrote:
> 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?

IIUC, bios are flushed to parent throttl group, so if there's an
ancestral limit, it should be honored. (I find this similar to memcg
reparenting.)

Mere create + set limit + delete falls under the same delegation scope,
so if that limit is bypassed, it is only self-shooting in the leg.
Shortening the lifetime of offlined structures is benefitial, no?

Michal

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