[PATCH] Fix PG_launder

Set PG_launder against pages which are under VM writeback.  So page
allocators will throttle against them.

fs/fs-writeback.c

@@ -17,6 +17,7 @@
 #include <linux/spinlock.h>
 #include <linux/sched.h>
 #include <linux/fs.h>
+#include <linux/mm.h>
 #include <linux/writeback.h>
 
 /**
@@ -135,7 +136,7 @@ static void __sync_single_inode(struct inode *inode, int wait, int *nr_to_write)
 	if (mapping->a_ops->writeback_mapping)
 		mapping->a_ops->writeback_mapping(mapping, nr_to_write);
 	else
-		filemap_fdatawrite(mapping);
+		generic_writeback_mapping(mapping, NULL);
 
 	/* Don't write the inode if only I_DIRTY_PAGES was set */
 	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC))

include/linux/page-flags.h

@@ -174,6 +174,7 @@ extern void get_page_state(struct page_state *ret);
 
 #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)

mm/filemap.c

@@ -659,7 +659,6 @@ EXPORT_SYMBOL(wait_on_page_writeback);
 void unlock_page(struct page *page)
 {
 	wait_queue_head_t *waitqueue = page_waitqueue(page);
-	clear_bit(PG_launder, &(page)->flags);
 	smp_mb__before_clear_bit();
 	if (!TestClearPageLocked(page))
 		BUG();
@@ -674,7 +673,7 @@ void unlock_page(struct page *page)
 void end_page_writeback(struct page *page)
 {
 	wait_queue_head_t *waitqueue = page_waitqueue(page);
-	clear_bit(PG_launder, &(page)->flags);
+	ClearPageLaunder(page);
 	smp_mb__before_clear_bit();
 	if (!TestClearPageWriteback(page))
 		BUG();

mm/page-writeback.c

@@ -354,6 +354,8 @@ int generic_writeback_mapping(struct address_space *mapping, int *nr_to_write)
 		lock_page(page);
 
 		if (TestClearPageDirty(page)) {
+			if (current->flags & PF_MEMALLOC)
+				SetPageLaunder(page);
 			err = writepage(page);
 			if (!ret)
 				ret = err;