On Wed 29-06-11 16:12:34, Christoph Hellwig wrote:
> On Wed, Jun 29, 2011 at 09:15:18PM +0200, Jan Kara wrote:
> > True but writeback_single_inode() has in it:
> > if (wbc->sync_mode == WB_SYNC_ALL) {
> > int err = filemap_fdatawait(mapping);
> > if (ret == 0)
> > ret = err;
> > }
> > So we end up waiting much earlier. Probably we should remove this wait
> > but that will need some audit I guess.
>
> Uhh, indeed. We'll need this wait for things like sync_inode, though.
Yes. Actually, specifically for filesystems like XFS which update inode
after IO completion we would need more passes to be efficient and correct:
for all inodes
fdatawrite
for all inodes
fdatawait
for all inodes
write_inode
for all inodes
wait for inode IO
But maybe this could be handled by having new WB_SYNC_ mode indicating
that writeback_single_inode() should not bother waiting (thus we'd really
end up waiting in sync_inodes_sb()) and then XFS and other filesystems that
need it would writeout inodes in their sync_fs() implementation (possibly
using a generic helper)?
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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