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

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Message-ID: <alpine.LFD.1.10.0807030942440.18105@woody.linux-foundation.org>
Date:	Thu, 3 Jul 2008 09:44:27 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
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 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..

		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 */
--
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