[PATCH] Swap Migration V5: Add CONFIG_MIGRATION for page migration support

Include page migration if the system is NUMA or having a memory model that
allows distinct areas of memory (SPARSEMEM, DISCONTIGMEM).

And:
- Only include lru_add_drain_per_cpu if building for an SMP system.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/swap.h

@@ -178,7 +178,9 @@ extern int vm_swappiness;
 extern int isolate_lru_page(struct page *p);
 extern int putback_lru_pages(struct list_head *l);
 
+#ifdef CONFIG_MIGRATION
 extern int migrate_pages(struct list_head *l, struct list_head *t);
+#endif
 
 #ifdef CONFIG_MMU
 /* linux/mm/shmem.c */

mm/Kconfig

@@ -132,3 +132,10 @@ config SPLIT_PTLOCK_CPUS
 	default "4096" if ARM && !CPU_CACHE_VIPT
 	default "4096" if PARISC && !PA20
 	default "4"
+
+#
+# support for page migration
+#
+config MIGRATION
+	def_bool y if NUMA || SPARSEMEM || DISCONTIGMEM
+	depends on SWAP

mm/vmscan.c

@@ -568,6 +568,7 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
 	return reclaimed;
 }
 
+#ifdef CONFIG_MIGRATION
 /*
  * swapout a single page
  * page is locked upon entry, unlocked on exit
@@ -656,8 +657,9 @@ int migrate_pages(struct list_head *l, struct list_head *t)
 
 		/*
 		 * Skip locked pages during the first two passes to give the
-		 * functions holding the lock time to release the page. Later we use
-		 * lock_page to have a higher chance of acquiring the lock.
+		 * functions holding the lock time to release the page. Later we
+		 * use lock_page() to have a higher chance of acquiring the
+		 * lock.
 		 */
 		if (pass > 2)
 			lock_page(page);
@@ -669,15 +671,15 @@ int migrate_pages(struct list_head *l, struct list_head *t)
 		 * Only wait on writeback if we have already done a pass where
 		 * we we may have triggered writeouts for lots of pages.
 		 */
-		if (pass > 0)
+		if (pass > 0) {
 			wait_on_page_writeback(page);
-		else
+		} else {
 			if (PageWriteback(page)) {
 				unlock_page(page);
 				goto retry_later;
 			}
+		}
 
-#ifdef CONFIG_SWAP
 		if (PageAnon(page) && !PageSwapCache(page)) {
 			if (!add_to_swap(page)) {
 				unlock_page(page);
@@ -686,16 +688,15 @@ int migrate_pages(struct list_head *l, struct list_head *t)
 				continue;
 			}
 		}
-#endif /* CONFIG_SWAP */
 
 		/*
 		 * Page is properly locked and writeback is complete.
 		 * Try to migrate the page.
 		 */
-		if (swap_page(page)) {
+		if (!swap_page(page))
+			continue;
 retry_later:
-			retry++;
-		}
+		retry++;
 	}
 	if (retry && pass++ < 10)
 		goto redo;
@@ -708,6 +709,7 @@ int migrate_pages(struct list_head *l, struct list_head *t)
 
 	return nr_failed + retry;
 }
+#endif
 
 /*
  * zone->lru_lock is heavily contended.  Some of the functions that