linux-kernel - [PATCH 04/18] mm: numa: Do not clear PMD during PTE update scan

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Message-Id: <1386690695-27380-5-git-send-email-mgorman@suse.de>
Date:	Tue, 10 Dec 2013 15:51:22 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alex Thorlton <athorlton@....com>, Rik van Riel <riel@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 04/18] mm: numa: Do not clear PMD during PTE update scan

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.

Cc: stable@...r.kernel.org
Signed-off-by: Mel Gorman <mgorman@...e.de>
Reviewed-by: Rik van Riel <riel@...hat.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 deae592..5a5da50 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1529,7 +1529,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 			 */
 			if (!is_huge_zero_page(page) &&
 			    !pmd_numa(*pmd)) {
-				entry = pmdp_get_and_clear(mm, addr, pmd);
+				entry = *pmd;
 				entry = pmd_mknuma(entry);
 				ret = HPAGE_PMD_NR;
 			}
-- 
1.8.4

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