From 75f0190b8f4efe496097436fd8a159ae2b923480 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Wed, 14 May 2014 10:02:18 +1000
Subject: [PATCH] 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@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 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 d1fe1a761047..4d4b39ab2341 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 9f70e02111c6..f47fb38c4889 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);
-- 
2.39.5