linux-kernel - [PATCH 14/19] mm: shmem: Avoid atomic operation during shmem_getpage

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Message-Id: <1399974350-11089-15-git-send-email-mgorman@suse.de>
Date:	Tue, 13 May 2014 10:45:45 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>
Subject: [PATCH 14/19] mm: shmem: Avoid atomic operation during shmem_getpage_gfp

shmem_getpage_gfp uses an atomic operation to set the SwapBacked field
before it's even added to the LRU or visible. This is unnecessary as what
could it possible race against?  Use an unlocked variant.

Signed-off-by: Mel Gorman <mgorman@...e.de>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Rik van Riel <riel@...hat.com>
---
 include/linux/page-flags.h | 1 +
 mm/shmem.c                 | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d1fe1a7..4d4b39a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -208,6 +208,7 @@ PAGEFLAG(Pinned, pinned) TESTSCFLAG(Pinned, pinned)	/* Xen */
 PAGEFLAG(SavePinned, savepinned);			/* Xen */
 PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
 PAGEFLAG(SwapBacked, swapbacked) __CLEARPAGEFLAG(SwapBacked, swapbacked)
+	__SETPAGEFLAG(SwapBacked, swapbacked)
 
 __PAGEFLAG(SlobFree, slob_free)
 
diff --git a/mm/shmem.c b/mm/shmem.c
index 9f70e02..f47fb38 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1132,7 +1132,7 @@ repeat:
 			goto decused;
 		}
 
-		SetPageSwapBacked(page);
+		__SetPageSwapBacked(page);
 		__set_page_locked(page);
 		error = mem_cgroup_charge_file(page, current->mm,
 						gfp & GFP_RECLAIM_MASK);
-- 
1.8.4.5

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