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

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Message-ID: <47989711.3070708@users.sourceforge.net>
Date:	Thu, 24 Jan 2008 14:48:01 +0100 (MET)
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Naveen Gupta <ngupta@...gle.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Paul Menage <menage@...gle.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH] cgroup: limit block I/O bandwidth

Pavel Emelyanov wrote:
> Andrea Righi wrote:
>> Balbir Singh wrote:
>>> * Andrea Righi <righiandr@...rs.sourceforge.net> [2008-01-23 16:23:59]:
>>>
>>>> Probably tracking who dirtied the pages would be the best approach, but
>>>> we want also to reduce the overhead of this tracking. So, we should find
>>>> a smart way to track which cgroup dirtied the pages and then only when
>>>> the i/o scheduler dispatches the write requests of those pages, account
>>>> the i/o operations to the opportune cgroup. In this way throttling could
>>>> be done probably in __set_page_dirty() as well.
>>>>
>>> I think the OpenVZ controller works that way.
>> Well... looking at the code it seems that OpenVZ doesn't use this
>> strategy, instead performs UBC-based I/O accounting looking at the
> 
> We do track the task (well - the beancounter) who made the page
> dirty and then use this context for async write scheduling.

Interesting... now I see that task_io_account_write() takes a
"struct page *" as argument and the "struct page" has the beancounter
pointer.

> 
>> __set_page_dirty*() for writes and submit_bio() for reads. Then,
>> independently from accounting data, it uses per-UBC i/o priority model
>> that is mapped directly on the CFQ i/o priority model.
> 
> Vasisly Tarasov (out I/O guru ;)) has already prepared an RFC patchset
> for Jens with group scheduler (for sync requests only) and is going to
> send it this or next week.
> 

Very good! I look forward for this patchset.

Thanks,
-Andrea
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