[PATCH] vmscan: add lru_to_page() helper

From: Nick Piggin <piggin@cyberone.com.au>

Add a little helper macro for a common list extraction operation in vmscan.c

mm/vmscan.c

@@ -43,14 +43,15 @@
 int vm_swappiness = 60;
 static long total_memory;
 
+#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
+
 #ifdef ARCH_HAS_PREFETCH
 #define prefetch_prev_lru_page(_page, _base, _field)			\
 	do {								\
 		if ((_page)->lru.prev != _base) {			\
 			struct page *prev;				\
 									\
-			prev = list_entry(_page->lru.prev,		\
-					struct page, lru);		\
+			prev = lru_to_page(&(_page->lru));		\
 			prefetch(&prev->_field);			\
 		}							\
 	} while (0)
@@ -64,8 +65,7 @@ static long total_memory;
 		if ((_page)->lru.prev != _base) {			\
 			struct page *prev;				\
 									\
-			prev = list_entry(_page->lru.prev,		\
-					struct page, lru);		\
+			prev = lru_to_page(&(_page->lru));			\
 			prefetchw(&prev->_field);			\
 		}							\
 	} while (0)
@@ -260,7 +260,7 @@ shrink_list(struct list_head *page_list, unsigned int gfp_mask, int *nr_scanned)
 		int may_enter_fs;
 		int referenced;
 
-		page = list_entry(page_list->prev, struct page, lru);
+		page = lru_to_page(page_list);
 		list_del(&page->lru);
 
 		if (TestSetPageLocked(page))
@@ -494,8 +494,7 @@ shrink_cache(struct zone *zone, unsigned int gfp_mask,
 
 		while (nr_scan++ < SWAP_CLUSTER_MAX &&
 				!list_empty(&zone->inactive_list)) {
-			page = list_entry(zone->inactive_list.prev,
-						struct page, lru);
+			page = lru_to_page(&zone->inactive_list);
 
 			prefetchw_prev_lru_page(page,
 						&zone->inactive_list, flags);
@@ -540,7 +539,7 @@ shrink_cache(struct zone *zone, unsigned int gfp_mask,
 		 * Put back any unfreeable pages.
 		 */
 		while (!list_empty(&page_list)) {
-			page = list_entry(page_list.prev, struct page, lru);
+			page = lru_to_page(&page_list);
 			if (TestSetPageLRU(page))
 				BUG();
 			list_del(&page->lru);
@@ -599,7 +598,7 @@ refill_inactive_zone(struct zone *zone, const int nr_pages_in,
 	pgmoved = 0;
 	spin_lock_irq(&zone->lru_lock);
 	while (nr_pages && !list_empty(&zone->active_list)) {
-		page = list_entry(zone->active_list.prev, struct page, lru);
+		page = lru_to_page(&zone->active_list);
 		prefetchw_prev_lru_page(page, &zone->active_list, flags);
 		if (!TestClearPageLRU(page))
 			BUG();
@@ -650,7 +649,7 @@ refill_inactive_zone(struct zone *zone, const int nr_pages_in,
 		reclaim_mapped = 1;
 
 	while (!list_empty(&l_hold)) {
-		page = list_entry(l_hold.prev, struct page, lru);
+		page = lru_to_page(&l_hold);
 		list_del(&page->lru);
 		if (page_mapped(page)) {
 			if (!reclaim_mapped) {
@@ -681,7 +680,7 @@ refill_inactive_zone(struct zone *zone, const int nr_pages_in,
 	pgmoved = 0;
 	spin_lock_irq(&zone->lru_lock);
 	while (!list_empty(&l_inactive)) {
-		page = list_entry(l_inactive.prev, struct page, lru);
+		page = lru_to_page(&l_inactive);
 		prefetchw_prev_lru_page(page, &l_inactive, flags);
 		if (TestSetPageLRU(page))
 			BUG();
@@ -710,7 +709,7 @@ refill_inactive_zone(struct zone *zone, const int nr_pages_in,
 
 	pgmoved = 0;
 	while (!list_empty(&l_active)) {
-		page = list_entry(l_active.prev, struct page, lru);
+		page = lru_to_page(&l_active);
 		prefetchw_prev_lru_page(page, &l_active, flags);
 		if (TestSetPageLRU(page))
 			BUG();