[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>

3 files changed, 20 insertions, 9 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 893096e67bdb..117add066f00 100644
--- a/include/linux/swap.h
+++ b/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 */
diff --git a/mm/Kconfig b/mm/Kconfig
index b3db11f137e0..a9cb80ae6409 100644
--- a/mm/Kconfig
+++ b/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
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a537a7f16357..58270aea669a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -568,6 +568,7 @@ keep:
         return reclaimed;
 }
 
+#ifdef CONFIG_MIGRATION
 /*
  * swapout a single page
  * page is locked upon entry, unlocked on exit
@@ -656,8 +657,9 @@ redo:
 
                 /*
                  * 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 @@ redo:
                  * 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 @@ redo:
                                 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 @@ retry_later:
 
         return nr_failed + retry;
 }
+#endif
 
 /*
  * zone->lru_lock is heavily contended.  Some of the functions that