mm: page_alloc: take the ALLOC_NO_WATERMARK check out of the fast path
authorMel Gorman <mgorman@suse.de>
Wed, 4 Jun 2014 23:10:14 +0000 (16:10 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 4 Jun 2014 23:54:09 +0000 (16:54 -0700)
commit5dab29113ca56335c78be3f98bf5ddf2ef8eb6a6
tree337e4f57205a98200e1c34675aa404f5301b6736
parenta6e21b14f22041382e832d30deda6f26f37b1097
mm: page_alloc: take the ALLOC_NO_WATERMARK check out of the fast path

ALLOC_NO_WATERMARK is set in a few cases.  Always by kswapd, always for
__GFP_MEMALLOC, sometimes for swap-over-nfs, tasks etc.  Each of these
cases are relatively rare events but the ALLOC_NO_WATERMARK check is an
unlikely branch in the fast path.  This patch moves the check out of the
fast path and after it has been determined that the watermarks have not
been met.  This helps the common fast path at the cost of making the slow
path slower and hitting kswapd with a performance cost.  It's a reasonable
tradeoff.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-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>
mm/page_alloc.c