linux-kernel - Re: [PATCH]vmscan: handle underflow for get_scan

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Message-Id: <20100406103500.7E2D.A69D9226@jp.fujitsu.com>
Date:	Tue,  6 Apr 2010 10:36:32 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Wu, Fengguang" <fengguang.wu@...el.com>
Subject: Re: [PATCH]vmscan: handle underflow for get_scan_ratio

> On Sun, Apr 04, 2010 at 10:19:06PM +0800, KOSAKI Motohiro wrote:
> > > On Fri, Apr 02, 2010 at 05:14:38PM +0800, KOSAKI Motohiro wrote:
> > > > > > > This patch makes a lot of sense than previous. however I think <1% anon ratio
> > > > > > > shouldn't happen anyway because file lru doesn't have reclaimable pages.
> > > > > > > <1% seems no good reclaim rate.
> > > > > > 
> > > > > > Oops, the above mention is wrong. sorry. only 1 page is still too big.
> > > > > > because under streaming io workload, the number of scanning anon pages should
> > > > > > be zero. this is very strong requirement. if not, backup operation will makes
> > > > > > a lot of swapping out.
> > > > > Sounds there is no big impact for the workload which you mentioned with the patch.
> > > > > please see below descriptions.
> > > > > I updated the description of the patch as fengguang suggested.
> > > > 
> > > > Umm.. sorry, no.
> > > > 
> > > > "one fix but introduce another one bug" is not good deal. instead, 
> > > > I'll revert the guilty commit at first as akpm mentioned.
> > > Even we revert the commit, the patch still has its benefit, as it increases
> > > calculation precision, right?
> > 
> > no, you shouldn't ignore the regression case.
> I don't think this is serious. In my calculation, there is only 1 page swapped out
> for 6G anonmous memory. 1 page should haven't any performance impact.

there is. I had received exactly opposite claim. because shrink_zone()
is not called only once. it is called very much time.




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