[PATCH] SwapMig: add_to_swap() avoid atomic allocations

Add gfp_mask to add_to_swap

add_to_swap does allocations with GFP_ATOMIC in order not to interfere with
swapping.  During migration we may have use add_to_swap extensively which may
lead to out of memory errors.

This patch makes add_to_swap take a parameter that specifies the gfp mask.
The page migration code can then make add_to_swap use GFP_KERNEL.

Signed-off-by: Hirokazu Takahashi <taka@valinux.co.jp>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
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

@@ -198,7 +198,7 @@ extern int rw_swap_page_sync(int, swp_entry_t, struct page *);
 extern struct address_space swapper_space;
 #define total_swapcache_pages  swapper_space.nrpages
 extern void show_swap_cache_info(void);
-extern int add_to_swap(struct page *);
+extern int add_to_swap(struct page *, gfp_t);
 extern void __delete_from_swap_cache(struct page *);
 extern void delete_from_swap_cache(struct page *);
 extern int move_to_swap_cache(struct page *, swp_entry_t);

mm/swap_state.c

@@ -141,7 +141,7 @@ void __delete_from_swap_cache(struct page *page)
  * Allocate swap space for the page and add the page to the
  * swap cache.  Caller needs to hold the page lock. 
  */
-int add_to_swap(struct page * page)
+int add_to_swap(struct page * page, gfp_t gfp_mask)
 {
 	swp_entry_t entry;
 	int err;
@@ -166,7 +166,7 @@ int add_to_swap(struct page * page)
 		 * Add it to the swap cache and mark it dirty
 		 */
 		err = __add_to_swap_cache(page, entry,
-				GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN);
+				gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
 
 		switch (err) {
 		case 0:				/* Success */

mm/vmscan.c

@@ -458,7 +458,7 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
 		 * Try to allocate it some swap space here.
 		 */
 		if (PageAnon(page) && !PageSwapCache(page)) {
-			if (!add_to_swap(page))
+			if (!add_to_swap(page, GFP_ATOMIC))
 				goto activate_locked;
 		}
 #endif /* CONFIG_SWAP */
@@ -715,7 +715,7 @@ redo:
 		}
 
 		if (PageAnon(page) && !PageSwapCache(page)) {
-			if (!add_to_swap(page)) {
+			if (!add_to_swap(page, GFP_KERNEL)) {
 				unlock_page(page);
 				list_move(&page->lru, &failed);
 				nr_failed++;