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

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Date:	Thu, 21 Oct 2010 08:22:22 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Nick Piggin <npiggin@...nel.dk>
Cc:	Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/21] fs: Implement lazy LRU updates for inodes

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.
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