Re: [PATCH 04/21] fs: Implement lazy LRU updates for inodes

Christoph Hellwig
2010-10-21T12:22:29Z

On Thu, Oct 21, 2010 at 09:07:06PM +1100, Nick Piggin wrote:
> On Thu, Oct 21, 2010 at 11:49:29AM +1100, Dave Chinner wrote:
> > } else {
> > /*
> > - * The inode is clean, unused
> > + * The inode is clean. If it is unused, then make sure
> > + * that it is put on the LRU correctly as iput_final()
> > + * does not move dirty inodes to the LRU and dirty
> > + * inodes are removed from the LRU during scanning.
> > */
> > - list_move(&inode->i_list, &inode_unused);
> > + list_del_init(&inode->i_list);
> > + if (!atomic_read(&inode->i_count))
> > + inode_lru_list_add(inode);
>
> This "optimisation" is surely wrong. How could we have no reference
> on the inode at this point?

Good question. iput_final does so for unlinked inodes or umount,
and that should be about it as it's the only place setting I_WILL_FREE
and we require that for a 0 refcount at the beginning of
writeback_single_inode. But adding it to the LRU case for that
is rather pointless as we will remove it a little bit later.

So I think the assignment can be safely removed, but I'd rather do in
a separate, properly documented patch rather than hiding it somewhere
unrelated. That patch could however go towards the beggining of the
series to make things easier.