From: Mel Gorman <mgor...@suse.de> 3.12-stable review patch. If anyone has any objections, please let me know.
=============== commit 5dab29113ca56335c78be3f98bf5ddf2ef8eb6a6 upstream. 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 <mgor...@suse.de> Acked-by: Johannes Weiner <han...@cmpxchg.org> Reviewed-by: Rik van Riel <r...@redhat.com> Cc: Vlastimil Babka <vba...@suse.cz> Cc: Jan Kara <j...@suse.cz> Cc: Michal Hocko <mho...@suse.cz> Cc: Hugh Dickins <hu...@google.com> Cc: Dave Hansen <dave.han...@intel.com> Cc: Theodore Ts'o <ty...@mit.edu> Cc: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> Cc: Oleg Nesterov <o...@redhat.com> Cc: Peter Zijlstra <pet...@infradead.org> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Mel Gorman <mgor...@suse.de> Signed-off-by: Jiri Slaby <jsl...@suse.cz> --- mm/page_alloc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index cb4cadddfd97..332066b098b5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1934,9 +1934,6 @@ zonelist_scan: (alloc_flags & ALLOC_CPUSET) && !cpuset_zone_allowed_softwall(zone, gfp_mask)) continue; - BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK); - if (unlikely(alloc_flags & ALLOC_NO_WATERMARKS)) - goto try_this_zone; /* * Distribute pages in proportion to the individual * zone size to ensure fair page aging. The zone a @@ -1983,6 +1980,11 @@ zonelist_scan: classzone_idx, alloc_flags)) { int ret; + /* Checked here to keep the fast path fast */ + BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK); + if (alloc_flags & ALLOC_NO_WATERMARKS) + goto try_this_zone; + if (IS_ENABLED(CONFIG_NUMA) && !did_zlc_setup && nr_online_nodes > 1) { /* -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html