linux-kernel - [PATCH 3.14 58/77] mm: shmem: avoid atomic operation during shmem_getpage

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Message-Id: <20150128012747.707647324@linuxfoundation.org>
Date:	Tue, 27 Jan 2015 17:27:36 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Theodore Tso <tytso@....edu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.14 58/77] mm: shmem: avoid atomic operation during shmem_getpage_gfp

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mel Gorman <mgorman@...e.de>

commit 07a427884348d38a6fd56fa4d78249c407196650 upstream.

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>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Jan Kara <jack@...e.cz>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Theodore Ts'o <tytso@....edu>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/page-flags.h |    1 +
 mm/shmem.c                 |    2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -208,6 +208,7 @@ PAGEFLAG(Pinned, pinned) TESTSCFLAG(Pinn
 PAGEFLAG(SavePinned, savepinned);			/* Xen */
 PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
 PAGEFLAG(SwapBacked, swapbacked) __CLEARPAGEFLAG(SwapBacked, swapbacked)
+	__SETPAGEFLAG(SwapBacked, swapbacked)

 __PAGEFLAG(SlobFree, slob_free)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1140,7 +1140,7 @@ repeat:
 			goto decused;
 		}

-		SetPageSwapBacked(page);
+		__SetPageSwapBacked(page);
 		__set_page_locked(page);
 		error = mem_cgroup_cache_charge(page, current->mm,
 						gfp & GFP_RECLAIM_MASK);

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