Re: [PATCH 1/3] xfs: implement per-inode writeback completion queues

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Apr 22, 2019 at 11:34:21PM -0700, Christoph Hellwig wrote:
> I'm a little late to the game, sorry..
> 
> But:
> 
> > +
> > +	spin_lock_irqsave(&ip->i_iodone_lock, flags);
> > +	list_replace_init(&ip->i_iodone_list, &completion_list);
> > +	spin_unlock_irqrestore(&ip->i_iodone_lock, flags);
> 
> I really don't like this new per-inode lock, and the irq disabling at
> all.  Especially as the pattern perfectly fits the lockless lists (llists).
> Can you check if these work here?

They certainly look promising, though the singly-linked list nature
means it can't be a direct replacement for xfs_ioend.io_list because we
still need to be able to sort and merge completions.  However, adding
another pointer to xfs_ioend won't change the objects per slab ratio, so
avoiding the spinlock heartburn might be worth it...

--D