page allocator: check only once if the zonelist is suitable for the a…

…llocation

It is possible with __GFP_THISNODE that no zones are suitable.  This patch
makes sure the check is only made once.

Signed-off-by: Mel Gorman <[email protected]>
Reviewed-by: Christoph Lameter <[email protected]>
Reviewed-by: KOSAKI Motohiro <[email protected]>
Reviewed-by: Pekka Enberg <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Lee Schermerhorn <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/page_alloc.c

@@ -1483,9 +1483,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	if (should_fail_alloc_page(gfp_mask, order))
 		return NULL;
 
-restart:
-	z = zonelist->_zonerefs;  /* the list of zones suitable for gfp_mask */
-
+	/* the list of zones suitable for gfp_mask */
+	z = zonelist->_zonerefs;
 	if (unlikely(!z->zone)) {
 		/*
 		 * Happens if we have an empty zonelist as a result of
@@ -1494,6 +1493,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 		return NULL;
 	}
 
+restart:
 	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
 			zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET);
 	if (page)