mm/page_alloc.c: use list_{first,last}_entry instead of list_entry

To make the intention clearer, use list_{first,last}_entry instead of
list_entry.
Signed-off-by: Geliang Tang <geliangtang@163.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -805,7 +805,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 		do {
 			int mt;	/* migratetype of the to-be-freed page */
 
-			page = list_entry(list->prev, struct page, lru);
+			page = list_last_entry(list, struct page, lru);
 			/* must delete as __free_one_page list manipulates */
 			list_del(&page->lru);
 
@@ -1410,11 +1410,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 	/* Find a page of the appropriate size in the preferred list */
 	for (current_order = order; current_order < MAX_ORDER; ++current_order) {
 		area = &(zone->free_area[current_order]);
-		if (list_empty(&area->free_list[migratetype]))
-			continue;
-
-		page = list_entry(area->free_list[migratetype].next,
+		page = list_first_entry_or_null(&area->free_list[migratetype],
 							struct page, lru);
+		if (!page)
+			continue;
 		list_del(&page->lru);
 		rmv_page_order(page);
 		area->nr_free--;
@@ -1693,11 +1692,11 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
 		for (order = 0; order < MAX_ORDER; order++) {
 			struct free_area *area = &(zone->free_area[order]);
 
-			if (list_empty(&area->free_list[MIGRATE_HIGHATOMIC]))
-				continue;
-
-			page = list_entry(area->free_list[MIGRATE_HIGHATOMIC].next,
+			page = list_first_entry_or_null(
+					&area->free_list[MIGRATE_HIGHATOMIC],
 					struct page, lru);
+			if (!page)
+				continue;
 
 			/*
 			 * It should never happen but changes to locking could
@@ -1746,7 +1745,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
 		if (fallback_mt == -1)
 			continue;
 
-		page = list_entry(area->free_list[fallback_mt].next,
+		page = list_first_entry(&area->free_list[fallback_mt],
 						struct page, lru);
 		if (can_steal)
 			steal_suitable_fallback(zone, page, start_migratetype);
@@ -2205,9 +2204,9 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
 		}
 
 		if (cold)
-			page = list_entry(list->prev, struct page, lru);
+			page = list_last_entry(list, struct page, lru);
 		else
-			page = list_entry(list->next, struct page, lru);
+			page = list_first_entry(list, struct page, lru);
 
 		list_del(&page->lru);
 		pcp->count--;