linux-kernel - Re: [PATCH] Do not clobber pgdat->nr_zones during memory initialisation

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Message-ID: <20080703171610.GG18055@csn.ul.ie>
Date:	Thu, 3 Jul 2008 18:16:10 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Andy Whitcroft <apw@...dowen.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, NeilBrown <neilb@...e.de>,
	babydr@...y-dragons.com, lee.schermerhorn@...com,
	a.beregalov@...il.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] Do not clobber pgdat->nr_zones during memory initialisation

On (03/07/08 09:44), Linus Torvalds didst pronounce:
> 
> 
> On Thu, 3 Jul 2008, Mel Gorman wrote:
> > 
> > Subject: [PATCH] Do not clobber pgdat->nr_zones during memory initialisation
> 
> Heh. I already applied it as ObviouslyCorrect(tm), but did the 
> simplification I already pointed out (and which your second version 
> already had) and rewrote your commit message a bit. So it's now committed 
> as follows..
> 

Perfect. The log even looks like it was written by a sane person. Thanks
for that.

> 		Linus
> 
> ---
> commit 494de90098784b8e2797598cefdd34188884ec2e
> Author: Mel Gorman <mel@....ul.ie>
> Date:   Thu Jul 3 05:27:51 2008 +0100
> 
>     Do not overwrite nr_zones on !NUMA when initialising zlcache_ptr
>     
>     The non-NUMA case of build_zonelist_cache() would initialize the
>     zlcache_ptr for both node_zonelists[] to NULL.
>     
>     Which is problematic, since non-NUMA only has a single node_zonelists[]
>     entry, and trying to zero the non-existent second one just overwrote the
>     nr_zones field instead.
>     
>     As kswapd uses this value to determine what reclaim work is necessary,
>     the result is that kswapd never reclaims.  This causes processes to
>     stall frequently in low-memory situations as they always direct reclaim.
>     This patch initialises zlcache_ptr correctly.
>     
>     Signed-off-by: Mel Gorman <mel@....ul.ie>
>     Tested-by: Dan Williams <dan.j.williams@...el.com>
>     [ Simplified patch a bit ]
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> ---
>  mm/page_alloc.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2f55295..f32fae3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2328,7 +2328,6 @@ static void build_zonelists(pg_data_t *pgdat)
>  static void build_zonelist_cache(pg_data_t *pgdat)
>  {
>  	pgdat->node_zonelists[0].zlcache_ptr = NULL;
> -	pgdat->node_zonelists[1].zlcache_ptr = NULL;
>  }
>  
>  #endif	/* CONFIG_NUMA */
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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