linux-kernel - Re: [PATCH] mm/vmscan.c: avoid recording the original scan targets in shrink

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Message-ID: <1402359051.22759.7.camel@debian>
Date:	Tue, 10 Jun 2014 08:10:51 +0800
From:	Chen Yucong <slaoub@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	mgorman@...e.de, mhocko@...e.cz, hannes@...xchg.org,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmscan.c: avoid recording the original scan targets
 in shrink_lruvec()

On Tue, 2014-06-10 at 08:24 +0900, Minchan Kim wrote:
> Hello,
> 
> On Mon, Jun 09, 2014 at 09:27:16PM +0800, Chen Yucong wrote:
> > Via https://lkml.org/lkml/2013/4/10/334 , we can find that recording the
> > original scan targets introduces extra 40 bytes on the stack. This patch
> > is able to avoid this situation and the call to memcpy(). At the same time,
> > it does not change the relative design idea.
> > 
> > ratio = original_nr_file / original_nr_anon;
> > 
> > If (nr_file > nr_anon), then ratio = (nr_file - x) / nr_anon.
> >  x = nr_file - ratio * nr_anon;
> > 
> > if (nr_file <= nr_anon), then ratio = nr_file / (nr_anon - x).
> >  x = nr_anon - nr_file / ratio;
> 
> Nice cleanup!
> 
> Below one nitpick.
> 

> 
> If both nr_file and nr_anon are zero, then the nr_anon could be zero
> if HugePage are reclaimed so that it could pass the below check
> 
>         if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
> 
> 
The Mel Gorman's patch has already handled this situation you're
describing. It's called:
 
mm: vmscan: use proportional scanning during direct reclaim and full
scan at DEF_PRIORITY

thx!
cyc

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