linux-kernel - Re: [PATCH -next] blk-throttle: enable io throttle for root in cgroup v2

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Message-ID: <20230206150005.GA21332@blackbody.suse.cz>
Date:   Mon, 6 Feb 2023 16:00:05 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Ofir Gal <ofir.gal@...umez.com>
Cc:     ming.lei@...hat.com, axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        tj@...nel.org, yi.zhang@...wei.com, yukuai3@...wei.com,
        Ofir Gal <ofir@....software>
Subject: Re: [PATCH -next] blk-throttle: enable io throttle for root in
 cgroup v2

On Sun, Feb 05, 2023 at 05:55:41PM +0200, Ofir Gal <ofir.gal@...umez.com> wrote:
> I have tried to limit the SSD on Server #1, but it seems that the NVME
> target kworkers are not affected unless I use Yu Kuai's patch.
> 
> Can you elaborate on the issues with this patch or how the scenario
> described above can be done with cgroups v2?

The issue is that if there's a client that doesn't implement
self-throttling you cannot guarantee anything on the server side.
Hence the mechanism must exist on the server side.

The NVME target should charge IO to respective blkcg's (just a generic
advice, I'm not familiar with that interface; see also
kthread_associate_blkcg() use in loop device driver).

HTH,
Michal

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