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>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d1fe1a761047683e555a9544dd5c668d5ae6752b..4d4b39ab2341ee182331dce062ab2fc2e90efe82 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 9f70e02111c6adcd090d8372ae0405b0f22b9abc..f47fb38c488994c062e9becc845e71ba6d9f80fe 100644 (file)
--- 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);