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SubjectRe: [Bug #10961] 2.6.26-rc: nfsd hangs for a few sec
On (01/07/08 18:04), Alexander Beregalov didst pronounce:
> 2008/7/1 Mel Gorman <>:
> > I still have no useful reaction to this. According to Christoph Hellwig,
> > this lockup has been appearing since lockdep was introduced but for some
> > reason is easier to trigger now. It bisected to the two-zonelist changes
> > but it still looks like a red herring as I cannot see how reclaim has
> > changed significantly as a result of that patch.
> Do you wait reaction from me? Can I help?
> As I mentioned, the lockup does not happen when lockdep is disabled.

Sorry for the slow response Alexander.

This bug is likely fixed by commit 494de90098784b8e2797598cefdd34188884ec2e
which will be visible publicly later when maintenance on
finishes. I included it below for convenience.
The lockdep warning still exists but it is a false positive and should be
relatively hard to trigger again. It would be nice to have confirmation
of this.

commit 494de90098784b8e2797598cefdd34188884ec2e
Author: Mel Gorman <>
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 <>
Tested-by: Dan Williams <>
[ Simplified patch a bit ]
Signed-off-by: Linus Torvalds <>
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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