linux-kernel - Re: [PATCH] cgroup: limit block I/O bandwidth

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Message-ID: <47936BC1.9060805@users.sourceforge.net>
Date:	Sun, 20 Jan 2008 16:41:54 +0100 (MET)
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Naveen Gupta <ngupta@...gle.com>, Paul Menage <menage@...gle.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cgroup: limit block I/O bandwidth

Jens Axboe wrote:
> Your approach is totally flawed, imho. For instance, you don't want a
> process to be able to dirty memory at foo mb/sec but only actually
> write them out at bar mb/sec.

Right. Actually my problem here is that the processes that write out
blocks are different respect to the processes that write bytes in
memory, and I would be able to add limits on those processes that are
dirtying memory.

> The noop-iosched changes are also very buggy. The queue back pointer
> breaks reference counting and the task pointer storage assumes the task
> will also always be around. That's of course not the case.

Yes, this really need a lot of fixes. I simply posted the patch to know
if such approach (in general) could have sense or not.

> IOW, you are doing this at the wrong level.
> 
> What problem are you trying to solve?

Limiting block I/O bandwidth for tasks that belong to a generic cgroup,
in order to provide a sort of a QoS on block I/O.

Anyway, I'm quite new in the wonderful land of the I/O scheduling, so
any help is appreciated.

Thanks,
-Andrea
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