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

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Date:	Tue, 6 Apr 2010 09:25:36 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	"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.

Thanks,
Shaohua
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