Re: [PATCH 2/7] writeback: switch to per-bdi threads for flushing data

[Christoph Hellwig <hch@infradead.org>]

On Mon, Mar 16, 2009 at 08:33:21AM +0100, Jens Axboe wrote:
> This is very useful feedback, thanks Dave. So on the filesystem vs bdi
> side, XFS could register a bdi per allocation group. Then set the proper
> inode->mapping->backing_dev_info from sb->s_op->alloc_inode and
> __mark_inode_dirty() should get the placement right. For private
> traverse and flush, provide some address_space op to override
> generic_sync_bdi_inodes().
> 
> It sounds like I should move the bdi flushing bits separate from the bdi
> itself. Embed one in the bdi, but allow outside registration of others.
> Will fit better with the need for more than one flusher per backing
> device.

Yes, having a separate flushing container is a good idea.  Either way
I'm not sure how much use all this is for XFS.  We're working on using
our own flushing code as we want to iterate the inodes using the
knowledge about their placement on disk.  Due to that we don't use
the dirty inode list anymore (already in mainline since 2.6.29-rc) but
the per-ag radix-tree.  The finer granularity pdflush management might
come in handy, but we'll hand off to some XFS-specific code at a pretty
high level in there.