linux-kernel - Re: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v7)

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Message-ID: <20100317133407.GA9198@redhat.com>
Date:	Wed, 17 Mar 2010 09:34:07 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Andrea Righi <arighi@...eler.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Peter Zijlstra <peterz@...radead.org>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v7)

On Wed, Mar 17, 2010 at 05:24:28PM +0530, Balbir Singh wrote:
> * Vivek Goyal <vgoyal@...hat.com> [2010-03-15 13:19:21]:
> 
> > On Mon, Mar 15, 2010 at 01:12:09PM -0400, Vivek Goyal wrote:
> > > On Mon, Mar 15, 2010 at 12:26:37AM +0100, Andrea Righi wrote:
> > > > Control the maximum amount of dirty pages a cgroup can have at any given time.
> > > > 
> > > > Per cgroup dirty limit is like fixing the max amount of dirty (hard to reclaim)
> > > > page cache used by any cgroup. So, in case of multiple cgroup writers, they
> > > > will not be able to consume more than their designated share of dirty pages and
> > > > will be forced to perform write-out if they cross that limit.
> > > > 
> > > 
> > > For me even with this version I see that group with 100M limit is getting
> > > much more BW.
> > > 
> > > root cgroup
> > > ==========
> > > #time dd if=/dev/zero of=/root/zerofile bs=4K count=1M
> > > 4294967296 bytes (4.3 GB) copied, 55.7979 s, 77.0 MB/s
> > > 
> > > real	0m56.209s
> > > 
> > > test1 cgroup with memory limit of 100M
> > > ======================================
> > > # time dd if=/dev/zero of=/root/zerofile1 bs=4K count=1M
> > > 4294967296 bytes (4.3 GB) copied, 20.9252 s, 205 MB/s
> > > 
> > > real	0m21.096s
> > > 
> > > Note, these two jobs are not running in parallel. These are running one
> > > after the other.
> > > 
> > 
> > Ok, here is the strange part. I am seeing similar behavior even without
> > your patches applied.
> > 
> > root cgroup
> > ==========
> > #time dd if=/dev/zero of=/root/zerofile bs=4K count=1M
> > 4294967296 bytes (4.3 GB) copied, 56.098 s, 76.6 MB/s
> > 
> > real	0m56.614s
> > 
> > test1 cgroup with memory limit 100M
> > ===================================
> > # time dd if=/dev/zero of=/root/zerofile1 bs=4K count=1M
> > 4294967296 bytes (4.3 GB) copied, 19.8097 s, 217 MB/s
> > 
> > real	0m19.992s
> > 
> 
> This is strange, did you flish the cache between the two runs?
> NOTE: Since the files are same, we reuse page cache from the
> other cgroup.

Files are different. Note suffix "1".

Vivek
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