Ok, so that means we need an equivalent fix in xfs_start_page_writeback()

as it will skip pages with clean buffers just like this. Something like

this (untested)?
---

 fs/xfs/linux-2.6/xfs_aops.c |    5 ++---

 1 file changed, 2 insertions(+), 3 deletions(-)
Index: 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_aops.c

===================================================================

--- 2.6.x-xfs-new.orig/fs/xfs/linux-2.6/xfs_aops.c	2007-10-02 16:12:56.000000000 +1000

+++ 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_aops.c	2007-10-03 07:53:27.866602431 +1000

@@ -420,10 +420,9 @@ xfs_start_page_writeback(

 		clear_page_dirty_for_io(page);

 	set_page_writeback(page);

 	unlock_page(page);

-	if (!buffers) {

+	/* If no buffers on the page are to be written, finish it here */

+	if (!buffers)

 		end_page_writeback(page);

-		wbc->pages_skipped++;	/* We didn't write this page */

-	}

 }
 static inline int bio_add_buffer(struct bio *bio, struct buffer_head *bh)
--

Dave Chinner

Principal Engineer

SGI Australian Software Group
-

Sure OK - as long as it is 'no write because of clean buffer'.

The only user of pages_skipped is obviously using that semantics.
Andrew, here is the expanded patch:

---

writeback: remove pages_skipped accounting in __block_write_full_page()
It can be produced by the following test scheme:
# cat bin/test-writeback.sh

grep nr_dirty /proc/vmstat

echo 1 > /proc/sys/fs/inode_debug

dd if=/dev/zero of=/var/x bs=1K count=204800&

while true; do grep nr_dirty /proc/vmstat; sleep 1; done
# bin/test-writeback.sh

nr_dirty 19207

nr_dirty 19207

nr_dirty 30924

204800+0 records in

204800+0 records out

209715200 bytes (210 MB) copied, 1.58363 seconds, 132 MB/s

nr_dirty 47150

nr_dirty 47141

nr_dirty 47142

nr_dirty 47142

nr_dirty 47142

nr_dirty 47142

nr_dirty 47205

nr_dirty 47214

nr_dirty 47214

nr_dirty 47214

nr_dirty 47214

nr_dirty 47214

nr_dirty 47215

nr_dirty 47216

nr_dirty 47216

nr_dirty 47216

nr_dirty 47154

nr_dirty 47143

nr_dirty 47143

nr_dirty 47143

nr_dirty 47143

nr_dirty 47143

nr_dirty 47142

nr_dirty 47142

nr_dirty 47142

nr_dirty 47142

nr_dirty 47134

nr_dirty 47134

nr_dirty 47135

nr_dirty 47135

nr_dirty 47135

nr_dirty 46097 <== -1038

nr_dirty 46098

nr_dirty 46098

nr_dirty 46098

[...]

nr_dirty 46091

nr_dirty 46092

nr_dirty 46092

nr_dirty 45069 <== -1023

nr_dirty 45056

nr_dirty 45056

nr_dirty 45056

[...]

nr_dirty 37822

nr_dirty 36799 <== -1023

[...]

nr_dirty 36781

nr_dirty 35758 <== -1023

[...]

nr_dirty 34708

nr_dirty 33672 <== -1024

[...]

nr_dirty 33692

nr_dirty 32669 <== -1023
% ls -li /var/x

847824 -rw-r--r-- 1 root root 200M 2007-08-12 04:12 /var/x
% dmesg|grep 847824  # generated by a debug printk

[  529.263184] redirtied inode 847824 line 548

[  564.250872] redirtied inode 847824 line 548

[  594.272797] redirtied inode 847824 line 548

[  629.231330] redirtied inode 847824 line 548

[  659.224674] redirtied inode 847824 line 548

[  689.219890] redirtied inode 847824 line 548

[  724.226655] redirtie...
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