[PATCH 3.8 086/166] mm: numa: do not clear PMD during PTE update scan

Kamal Mostafa
2014-01-15T21:51:40Z

From: Mel Gorman <mgorman@suse.de>

commit 5a6dac3ec5f583cc8ee7bc53b5500a207c4ca433 upstream.

If the PMD is flushed then a parallel fault in handle_mm_fault() will
enter the pmd_none and do_huge_pmd_anonymous_page() path where it'll
attempt to insert a huge zero page. This is wasteful so the patch
avoids clearing the PMD when setting pmd_numa.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
mm/huge_memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a72d5ca..5d7dc7c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1506,7 +1506,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
/* only check non-shared pages */
if (page_mapcount(page) == 1 &&
!pmd_numa(*pmd)) {
- entry = pmdp_get_and_clear(mm, addr, pmd);
+ entry = *pmd;
entry = pmd_mknuma(entry);
ret = HPAGE_PMD_NR;
}
--
1.8.3.2