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

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Message-ID: <20100317115427.GR18054@balbir.in.ibm.com>
Date:	Wed, 17 Mar 2010 17:24:28 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.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)

* 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.

-- 
	Three Cheers,
	Balbir
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