[PATCH 03/11] writeback: replace redirty_tail() on more-pages-to-sync

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

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Replace redirty_tail() with requeue_io()/requeue_io_wait() when
there are more pages to sync. There won't be starvation.

Cc: Michael Rubin <mrubin@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 fs/fs-writeback.c |   43 ++++++++-----------------------------------
 1 file changed, 8 insertions(+), 35 deletions(-)

--- linux-2.6.24-rc6-mm1.orig/fs/fs-writeback.c
+++ linux-2.6.24-rc6-mm1/fs/fs-writeback.c
@@ -273,46 +273,19 @@ __sync_single_inode(struct inode *inode,
 	if (!(inode->i_state & I_FREEING)) {
 		if (!(inode->i_state & I_DIRTY) &&
 		    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
 			/*
 			 * We didn't write back all the pages.  nfs_writepages()
-			 * sometimes bales out without doing anything. Redirty
-			 * the inode; Move it from s_io onto s_more_io/s_dirty.
+			 * sometimes bales out without doing anything.
 			 */
-			/*
-			 * akpm: if the caller was the kupdate function we put
-			 * this inode at the head of s_dirty so it gets first
-			 * consideration.  Otherwise, move it to the tail, for
-			 * the reasons described there.  I'm not really sure
-			 * how much sense this makes.  Presumably I had a good
-			 * reasons for doing it this way, and I'd rather not
-			 * muck with it at present.
-			 */
-			if (wbc->for_kupdate) {
-				/*
-				 * For the kupdate function we move the inode
-				 * to s_more_io so it will get more writeout as
-				 * soon as the queue becomes uncongested.
-				 */
-				inode->i_state |= I_DIRTY_PAGES;
-				if (wbc->nr_to_write > 0)
-					/* somehow blocked: wait and retry */
-					requeue_io_wait(inode);
-				else
-					/* slice used up: queue for next turn */
-					requeue_io(inode);
-			} else {
-				/*
-				 * Otherwise fully redirty the inode so that
-				 * other inodes on this superblock will get some
-				 * writeout.  Otherwise heavy writing to one
-				 * file would indefinitely suspend writeout of
-				 * all the other files.
-				 */
-				inode->i_state |= I_DIRTY_PAGES;
-				redirty_tail(inode);
-			}
+			inode->i_state |= I_DIRTY_PAGES;
+			if (wbc->nr_to_write > 0)
+				/* somehow blocked: wait and retry */
+				requeue_io_wait(inode);
+			else
+				/* slice used up: queue for next turn */
+				requeue_io(inode);
 		} else if (inode->i_state & I_DIRTY) {
 			/*
 			 * Someone redirtied the inode while were writing back
 			 * the pages.
 			 */

--