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SubjectRe: [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@csn.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@csn.ul.ie>
Tested-by: Dan Williams <dan.j.williams@intel.com>
[ Simplified patch a bit ]
Signed-off-by: Linus Torvalds <torvalds@linux-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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