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Subject[PATCH 04/13] writeback: dont redirty tail an inode with dirty pages
This extends commit b3af9468ae (writeback: don't delay inodes redirtied
by a fast dirtier) to the !kupdate case.

It also simplifies logic. Note that the I_DIRTY_PAGES test/handling is
merged into the PAGECACHE_TAG_DIRTY case. I_DIRTY_PAGES (at the line
removed by this patch) means there are _new_ pages get dirtied during
writeback, while PAGECACHE_TAG_DIRTY means there are dirty pages. In
this sense, the PAGECACHE_TAG_DIRTY test covers the I_DIRTY_PAGES case.

In *_set_page_dirty*(), PAGECACHE_TAG_DIRTY is set racelessly, while
I_DIRTY_PAGES might be set on the inode for a page just truncated. It
has no real impact on this patch -- it's actually slightly better now.

afs_fsync() always set I_DIRTY_PAGES after calling afs_writepages(),
maybe to keep the inode in the dirty list. That's a different code path,
so won't impact the requeue-vs-redirty timing here permenantly.

CC: David Howells <dhowells@redhat.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Christoph Hellwig <hch@infradead.org>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/fs-writeback.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)
--- linux-next.orig/fs/fs-writeback.c 2010-07-11 09:13:30.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2010-07-12 23:26:06.000000000 +0800
@@ -367,18 +367,7 @@ writeback_single_inode(struct inode *ino
spin_lock(&inode_lock);
inode->i_state &= ~I_SYNC;
if (!(inode->i_state & I_FREEING)) {
- if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) {
- /*
- * More pages get dirtied by a fast dirtier.
- */
- goto select_queue;
- } else if (inode->i_state & I_DIRTY) {
- /*
- * At least XFS will redirty the inode during the
- * writeback (delalloc) and on io completion (isize).
- */
- redirty_tail(inode);
- } else if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
+ if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
/*
* We didn't write back all the pages. nfs_writepages()
* sometimes bales out without doing anything. Redirty
@@ -400,7 +389,6 @@ writeback_single_inode(struct inode *ino
* soon as the queue becomes uncongested.
*/
inode->i_state |= I_DIRTY_PAGES;
-select_queue:
if (wbc->nr_to_write <= 0) {
/*
* slice used up: queue for next turn
@@ -423,6 +411,14 @@ select_queue:
inode->i_state |= I_DIRTY_PAGES;
redirty_tail(inode);
}
+ } else if (inode->i_state & I_DIRTY) {
+ /*
+ * Filesystems can dirty the inode during writeback
+ * operations, such as delayed allocation during
+ * submission or metadata updates after data IO
+ * completion.
+ */
+ redirty_tail(inode);
} else if (atomic_read(&inode->i_count)) {
/*
* The inode is clean, inuse



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