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

From: Tejun Heo <tj@kernel.org>
To: "yukuai (C)" <yukuai3@huawei.com>
Cc: axboe@kernel.dk, cgroups@vger.kernel.org,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	yi.zhang@huawei.com
Subject: Re: [PATCH -next] blk-throttle: enable io throttle for root in cgroup v2
Date: Tue, 1 Feb 2022 07:20:32 -1000	[thread overview]
Message-ID: <Yflr4FzUTWsiLTC/@slm.duckdns.org> (raw)
In-Reply-To: <235b0757-d322-2b6e-3ab6-ecc8c82f8f1e@huawei.com>

Hello,

On Thu, Jan 27, 2022 at 10:36:38AM +0800, yukuai (C) wrote:
> In our case, the disk is provided by server, and such disk can be shared
> by multipul clients. Thus for the client side, the server is a higher
> level parent.
> 
> Theoretically, limit the io from server for each client is feasible,
> however, the main reason we don't want to do this is the following
> shortcoming:
> 
> client can still send io to server unlimited, we can just limit the
> amount of io that can complete from server, which might cause too much
> pressure on the server side.

I don't quite follow the "send io to server unlimited" part. Doesn't that
get limited by available number of requests? ie. if the server throttles,
the in-flight requests will take longer to complete which exhausts the
available requests and thus slows down the client. That's how it's supposed
to work on the local machine too.

Thanks.

-- 
tejun