mm, page_alloc: remove field from alloc_context

The classzone_idx can be inferred from preferred_zoneref so remove the
unnecessary field and save stack space.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dba8cfd..9da66e7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2771,7 +2771,7 @@
 
 		mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
 		if (!zone_watermark_fast(zone, order, mark,
-				       ac->classzone_idx, alloc_flags)) {
+				       ac_classzone_idx(ac), alloc_flags)) {
 			int ret;
 
 			/* Checked here to keep the fast path fast */
@@ -2794,7 +2794,7 @@
 			default:
 				/* did we reclaim enough */
 				if (zone_watermark_ok(zone, order, mark,
-						ac->classzone_idx, alloc_flags))
+						ac_classzone_idx(ac), alloc_flags))
 					goto try_this_zone;
 
 				continue;
@@ -3114,7 +3114,7 @@
 
 	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
 						ac->high_zoneidx, ac->nodemask)
-		wakeup_kswapd(zone, order, zonelist_zone_idx(ac->preferred_zoneref));
+		wakeup_kswapd(zone, order, ac_classzone_idx(ac));
 }
 
 static inline unsigned int
@@ -3422,8 +3422,6 @@
 		goto no_zone;
 	}
 
-	ac.classzone_idx = zonelist_zone_idx(ac.preferred_zoneref);
-
 	/* First allocation attempt */
 	page = get_page_from_freelist(alloc_mask, order, alloc_flags, &ac);
 	if (likely(page))