Eric Lee / smarc-ti-linux-kernel

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Commit 6a6d151242e4ae6b4988ff3fd10d808363f78784

Authored by Mel Gorman
Committed by Greg Kroah-Hartman
1 parent e1ca6f43c3
Exists in smarc-ti-linux-3.14.y and in 1 other branch processor-sdk-linux-01.00.00

mm: page_alloc: take the ALLOC_NO_WATERMARK check out of the fast path 

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

Showing 1 changed file with 5 additions and 3 deletions Side-by-side Diff

... ... @@ -1959,9 +1959,6 @@
1959 1959 (alloc_flags & ALLOC_CPUSET) &&
1960 1960 !cpuset_zone_allowed_softwall(zone, gfp_mask))
1961 1961 continue;
1962   - BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
1963   - if (unlikely(alloc_flags & ALLOC_NO_WATERMARKS))
1964   - goto try_this_zone;
1965 1962 /*
1966 1963 * Distribute pages in proportion to the individual
1967 1964 * zone size to ensure fair page aging. The zone a
... ... @@ -2007,6 +2004,11 @@
2007 2004 if (!zone_watermark_ok(zone, order, mark,
2008 2005 classzone_idx, alloc_flags)) {
2009 2006 int ret;
  2007 +
  2008 + /* Checked here to keep the fast path fast */
  2009 + BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
  2010 + if (alloc_flags & ALLOC_NO_WATERMARKS)
  2011 + goto try_this_zone;
2010 2012  
2011 2013 if (IS_ENABLED(CONFIG_NUMA) &&
2012 2014 !did_zlc_setup && nr_online_nodes > 1) {