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

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Date:   Tue, 21 Sep 2021 15:44:14 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     "yukuai (C)" <yukuai3@...wei.com>,
        Khazhy Kumykov <khazhy@...gle.com>
Cc:     tj@...nel.org, axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [RFC PATCH] blk-throttle: enable io throttle for root in cgroup
 v2

On Sun, Sep 19, 2021 at 06:31:38PM +0800, "yukuai (C)" <yukuai3@...wei.com> wrote:
> Our use case is similair to this, a host can provide several remote
> devices to difierent client. If one client is under high io pressure,
> other client might be affected. Thus we want to limit the overall
> iops/bps from the client.

I see where are you coming from now. (Perhaps I'd suggest
allocating/prioritizing the allowances on the hosting side. If simply
wrapping "everything" into a non-root cgroup is not enough.)

On 2021/09/18 3:58, Khazhy Kumykov wrote:
> (This does also bring up: if this is a useful thing, would it make
> sense to tie to the device, vs. requiring cgroup. We happen to use
> cgroups so that requirement doesn't affect us).

Good point, That's IMO a better idea, it'd be more consistent with other
resources for which there exist global (cgroup independent) kernel
constraints (e.g. threads-max sysctl, mem= cmdline, cpu hotplug) that
double the root cgroup contraint role.

OTOH, this also deepens the precedent of init NS root cgroup being
special (more special than a container's root cgroup).

My .02€,
Michal