[PATCH] mm, page_alloc: Restore the original nodemask if the fast path allocation failed

(Andrew, this is on top of the pagealloc optimisation series in mmotm. It
 could be classed as a fix-up but it's subtle enough that it deserves its
 own changelog. "Clever" fixes had other consequences.)

The page allocator fast path uses either the requested nodemask or
cpuset_current_mems_allowed if cpusets are enabled. If the allocation
context allows watermarks to be ignored then it can also ignore memory
policies. However, on entering the allocator slowpath the nodemask may
still be cpuset_current_mems_allowed and the policies are enforced.
This patch resets the nodemask appropriately before entering the slowpath.

Signed-off-by: Vlastimil Babka <redacted>
Signed-off-by: Mel Gorman <redacted>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 79100583b9de..ec5155ab1482 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -3637,6 +3637,12 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	alloc_mask = memalloc_noio_flags(gfp_mask);
 	ac.spread_dirty_pages = false;
 
+	/*
+	 * Restore the original nodemask if it was potentially replaced with
+	 * &cpuset_current_mems_allowed to optimize the fast-path attempt.
+	 */
+	if (cpusets_enabled())
+		ac.nodemask = nodemask;
 	page = __alloc_pages_slowpath(alloc_mask, order, &ac);
 
 no_zone:

-- 
Mel Gorman
SUSE Labs

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