[PATCH] remove PG_launder

Removal of PG_launder.

It's not obvious (to me) why this ever existed.  If it's to prevent
deadlocks then I'd like to know who was performing __GFP_FS allocations
while holding a page lock?

But in 2.5, the only memory allocations which are performed when the
caller holds PG_writeback against an unsubmitted page are those which
occur inside submit_bh().  There will be no __GFS_FS allocations in
that call chain.

Removing PG_launder means that memory allocators can block on any
PageWriteback() page at all, which reduces the risk of very long list
walks inside pagemap_lru_lock in shrink_cache().

include/linux/page-flags.h

@@ -62,9 +62,8 @@
 #define PG_arch_1		10
 #define PG_reserved		11
 
-#define PG_launder		12	/* written out by VM pressure.. */
-#define PG_private		13	/* Has something at ->private */
-#define PG_writeback		14	/* Page is under writeback */
+#define PG_private		12	/* Has something at ->private */
+#define PG_writeback		13	/* Page is under writeback */
 
 /*
  * Global page accounting.  One instance per CPU.
@@ -172,10 +171,6 @@ extern void get_page_state(struct page_state *ret);
 #define SetPageReserved(page)	set_bit(PG_reserved, &(page)->flags)
 #define ClearPageReserved(page)	clear_bit(PG_reserved, &(page)->flags)
 
-#define PageLaunder(page)	test_bit(PG_launder, &(page)->flags)
-#define SetPageLaunder(page)	set_bit(PG_launder, &(page)->flags)
-#define ClearPageLaunder(page)	clear_bit(PG_launder, &(page)->flags)
-
 #define SetPagePrivate(page)	set_bit(PG_private, &(page)->flags)
 #define ClearPagePrivate(page)	clear_bit(PG_private, &(page)->flags)
 #define PagePrivate(page)	test_bit(PG_private, &(page)->flags)

mm/filemap.c

@@ -432,7 +432,7 @@ void invalidate_inode_pages2(struct address_space * mapping)
 int fail_writepage(struct page *page)
 {
 	/* Only activate on memory-pressure, not fsync.. */
-	if (PageLaunder(page)) {
+	if (current->flags & PF_MEMALLOC) {
 		activate_page(page);
 		SetPageReferenced(page);
 	}
@@ -652,7 +652,6 @@ void unlock_page(struct page *page)
 void end_page_writeback(struct page *page)
 {
 	wait_queue_head_t *waitqueue = page_waitqueue(page);
-	ClearPageLaunder(page);
 	smp_mb__before_clear_bit();
 	if (!TestClearPageWriteback(page))
 		BUG();

mm/page-writeback.c

@@ -373,8 +373,6 @@ int generic_writeback_mapping(struct address_space *mapping, int *nr_to_write)
 				}
 				spin_unlock(&pagemap_lru_lock);
 			}
-			if (current->flags & PF_MEMALLOC)
-				SetPageLaunder(page);
 			err = writepage(page);
 			if (!ret)
 				ret = err;

mm/shmem.c

@@ -438,7 +438,8 @@ static int shmem_writepage(struct page * page)
 
 	if (!PageLocked(page))
 		BUG();
-	if (!PageLaunder(page))
+
+	if (!(current->flags & PF_MEMALLOC))
 		return fail_writepage(page);
 
 	mapping = page->mapping;

mm/vmscan.c

@@ -424,11 +424,10 @@ static int shrink_cache(int nr_pages, zone_t * classzone, unsigned int gfp_mask,
 			goto page_mapped;
 
 		/*
-		 * The page is locked. IO in progress?
-		 * Move it to the back of the list.
+		 * IO in progress? Leave it at the back of the list.
 		 */
 		if (unlikely(PageWriteback(page))) {
-			if (PageLaunder(page) && (gfp_mask & __GFP_FS)) {
+			if (gfp_mask & __GFP_FS) {
 				page_cache_get(page);
 				spin_unlock(&pagemap_lru_lock);
 				wait_on_page_writeback(page);