linux-kernel - Re: [RFC][PATCH 7/8] memcg soft limit LRU reorder

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Message-Id: <20090331151929.3d958a95.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 31 Mar 2009 15:19:29 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC][PATCH 7/8] memcg soft limit LRU reorder

On Tue, 31 Mar 2009 11:36:07 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-31 09:00:23]:
> 
> > On Mon, 30 Mar 2009 13:22:46 +0530
> > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > 
> > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-27 14:12:25]:
> > > 
> > > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > > > 
> > > > This patch adds a function to change the LRU order of pages in global LRU
> > > > under control of memcg's victim of soft limit.
> > > > 
> > > > FILE and ANON victim is divided and LRU rotation will be done independently.
> > > > (memcg which only includes FILE cache or ANON can exists.)
> > > > 
> > > > The routine finds specfied number of pages from memcg's LRU and
> > > > move it to top of global LRU. They will be the first target of shrink_xxx_list.
> > > 
> > > This seems to be the core of the patch, but I don't like this very
> > > much. Moving LRU pages of the mem cgroup seems very subtle, why can't
> > > we directly use try_to_free_mem_cgroup_pages()?
> > > 
> > It ignores many things.
> 
> My concern is that such subtle modification to the global LRU 
> 
okay. maybe everyone's concern.

> 1. Can break the age property of elements in the LRU (we have mixed
> ages now in the LRU)

We have to break(change) some, anyway.
I think this kind of LRU-swapping/reorder technique is a popular technique to
give LRU a hint and reordering is one of the least invasive options.
It doesn't affect global LRU other than the order of pages and all statistics
are updated in sane way.


> 2. Can potentially impact lumpy reclaim, since we've mix LRU pages
> from the memory controlelr into the global LRU?
> 

I can't catch what you ask...but I think no influence to lumpty reclaim.
It gathers vicitm pages from neiborhood of a page which should be removed.
Hmm ?


Thanks,
-Kame

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