linux-kernel - Re: cgroup memory, blkio and the lovely swapping

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Message-Id: <20110304165455.d438342a.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 4 Mar 2011 16:54:55 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	linux-kernel@...r.kernel.org
Cc:	Daniel Poelzleithner <poelzi@...lzi.org>, linux-mm@...ck.org,
	containers@...ts.linux-foundation.org
Subject: Re: cgroup memory, blkio and the lovely swapping

On Fri, 4 Mar 2011 08:39:44 +0100
Daniel Poelzleithner <poelzi@...lzi.org> wrote:

> Hi,
> 
> currently when one process causes heavy swapping, the responsiveness of
> the hole system suffers greatly. With the small memleak [1] test tool I
> wrote, the effect can be experienced very easily, depending on the
> delay the lag can become quite large. If I ensure that 10% of the RAM
> stay free for free memory and cache, the system never swaps to death.
> That works very well, but if accesses to the swap are very heavy, the
> system still lags on all other processes, not only the swapping one.
> Putting the swapping process into a blkio cgroup with little weight does
> not affect the io or swap io from other processes with larger weight in
> their group.
> 
> Maybe I'm mistaken, but wouldn't it be the easiest way to get fair
> swapping and control to let the pagein respect the blkio.weight value
> or even better add a second weight value for swapping io ?
> 

Now, blkio cgroup does work only with synchronous I/O(direct I/O)
and never work with swap I/O. And I don't think swap-i/o limit
is a blkio matter.

Memory cgroup is now developping dirty_ratio for memory cgroup.
By that, you can control the number of pages in writeback, in memory cgroup.
I think it will work for you.

Thanks,
-Kame

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