linux-kernel - Re: [PATCH 2/3] i/o bandwidth controller infrastructure

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Date:	Fri, 27 Jun 2008 12:53:28 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	balbir@...ux.vnet.ibm.com, menage@...gle.com, chlunde@...g.uio.no,
	axboe@...nel.dk, matt@...ehost.com, roberto@...it.it,
	randy.dunlap@...cle.com, dpshah@...gle.com,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] i/o bandwidth controller infrastructure

Andrew Morton wrote:
> On Fri, 27 Jun 2008 00:36:46 +0200
> Andrea Righi <righi.andrea@...il.com> wrote:
> 
>>> Does all this code treat /dev/sda1 as a separate device from /dev/sda2?
>>>  If so, that would be broken.
>> Yes, all the partitions are treated as separate devices with
>> (potentially) different limiting rules, but I don't understand why it
>> would be broken... dev_t has both minor and major numbers, so it would
>> be possible to select single partitions as well.
> 
> Well it's functionally broken, isn't it?  A physical disk has a fixed
> IO bandwidth and when the administrator wants to partition that
> bandwidth amongst control groups he will need to consider the entire
> device when doing so?
> 
> I mean, the whole point of this feature and of control groups as a
> whole is isolation.  But /dev/sda1 and /dev/sda2 are very much _not_
> isolated.  Whereas /dev/sda and /dev/sdb are (to a large degree)
> isolated.

well... yes, sounds reasonable. In this case we could just ignore the
minor number and consider only major number as the key to identify a
specific block device (both for userspace<->kernel interface and when
accounting/throttling i/o requests).

-Andrea
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