[PATCH] Fix nfs writepage behaviour

From: Nick Piggin <nickpiggin@yahoo.com.au>

nfs_writepage() refuses to write back mapped pages at all on the page
reclaim path, causing systems to get locked up when there's a lot of dirty
mmapped data around.  The patch changes NFS so that it will start I/O
against these pages.

The code as it stands is designed to defer writeout to pdflush which can do
larger, more efficient I/Os.  But there shouldn't be much traffic by this
path, and going slow is better than not going at all.

Patch originally from Trond.
Signed-off-by: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/nfs/write.c

@@ -314,7 +314,7 @@ int nfs_writepage(struct page *page, struct writeback_control *wbc)
 		if (err >= 0) {
 			err = 0;
 			if (wbc->for_reclaim)
-				err = WRITEPAGE_ACTIVATE;
+				nfs_flush_inode(inode, 0, 0, FLUSH_STABLE);
 		}
 	} else {
 		err = nfs_writepage_sync(NULL, inode, page, 0,
@@ -327,8 +327,7 @@ int nfs_writepage(struct page *page, struct writeback_control *wbc)
 	}
 	unlock_kernel();
 out:
-	if (err != WRITEPAGE_ACTIVATE)
-		unlock_page(page);
+	unlock_page(page);
 	if (inode_referenced)
 		iput(inode);
 	return err;