linux-kernel - Re: [PATCH -mmotm 0/5] memcg: per cgroup dirty limit (v6)

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Date:	Thu, 11 Mar 2010 10:14:25 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Vivek Goyal <vgoyal@...hat.com>,
	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 (v6)

On Thu, 2010-03-11 at 10:17 +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 11 Mar 2010 09:39:13 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > > The performance overhead is not so huge in both solutions, but the impact on
> > > performance is even more reduced using a complicated solution...
> > > 
> > > Maybe we can go ahead with the simplest implementation for now and start to
> > > think to an alternative implementation of the page_cgroup locking and
> > > charge/uncharge of pages.

FWIW bit spinlocks suck massive.

> > 
> > maybe. But in this 2 years, one of our biggest concerns was the performance.
> > So, we do something complex in memcg. But complex-locking is , yes, complex.
> > Hmm..I don't want to bet we can fix locking scheme without something complex.
> > 
> But overall patch set seems good (to me.) And dirty_ratio and dirty_background_ratio
> will give us much benefit (of performance) than we lose by small overheads.

Well, the !cgroup or root case should really have no performance impact.

> IIUC, this series affects trgger for background-write-out.

Not sure though, while this does the accounting the actual writeout is
still !cgroup aware and can definately impact performance negatively by
shrinking too much.
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