mm: shmem: avoid atomic operation during shmem_getpage_gfp

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@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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index ca71a1d347a0870666faad2f76cbf55230bbe2e4..cffeaa9aea21559e48a0a5d9f5fcffef9cf6daf4 100644 (file)
--- 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 0f1447563f1753c8aa867fc985b38f7fa2a464af..706331e9ee0ae473f87e245e63f77d6ac1a9851a 100644 (file)
--- 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);