Re: Problem with delayed allocation

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On Mon, Aug 04, 2008 at 08:22:49PM +0530, Aneesh Kumar K.V wrote:
> On Sat, Aug 02, 2008 at 04:07:19PM -0400, Theodore Ts'o wrote:
> > 
> > Apparently __fsync_super(), which is called right before remounting a
> > filesystem read-only, isn't working correctly.  To reproduce, create a
> > script which does this:
> > 
> > #!/bin/sh
> > DEVICE=/dev/closure/test
> > mke2fs -t ext4dev /dev/closure/test
> > mount $DEVICE /mnt
> > cd /mnt
> > tar xfj /var/tmp/linux-2.6.26.tar.gz  <----- or some really big file
> > du -s
> > cd ..
> > mount -o remount,ro /mnt
> > sync
> > dmesg > /tmp/dmesg.out  <----- note all of the ext4_da_writepages error messages
> > umount /mnt
> > du -s /mnt
> > sync
> > mount $DEVICE /mnt
> > du -s /mnt    <---  note that size of the unpacked hierarcy is much smaller
> > 
> > This doesn't happen if the ext4 filesystem is mounted with nodelalloc,
> > so I assume the problem is in ext4_da_writepages().
> > 
> 
> Can you try this patch and see if it makes any difference ?
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 25adfc3..5a8a2d3 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -518,6 +518,7 @@ void generic_sync_sb_inodes(struct super_block *sb,
>  		spin_lock(&inode_lock);
>  		if (wbc->nr_to_write <= 0) {
>  			wbc->more_io = 1;
> +			printk(KERN_CRIT "Breaking from the %s loop\n", __func__);
>  			break;
>  		}
>  		if (!list_empty(&sb->s_more_io))
> @@ -611,6 +612,8 @@ void sync_inodes_sb(struct super_block *sb, int wait)
>  			(inodes_stat.nr_inodes - inodes_stat.nr_unused) +
>  			nr_dirty + nr_unstable;
>  	wbc.nr_to_write += wbc.nr_to_write / 2;		/* Bit more for luck */
> +	wbc.nr_to_write =  LONG_MAX;
> +
>  	sync_sb_inodes(sb, &wbc);
>  }
>  


I guess this could be the reason. I am not hitting the error during
remount, ro with this change. But I have other changes also accumulated
as a part of rewrite.


diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4a50445..ecabe77 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2225,8 +2288,10 @@ static int ext4_da_writepages(struct address_space *mapping,
 	if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
 		return 0;
 
+#if 0
 	if (wbc->nr_to_write > mapping->nrpages)
 		wbc->nr_to_write = mapping->nrpages;
+#endif
 
 
 	if (!wbc->range_cyclic) {