Re: [PATCH 1/3] writeback: simplify the write back thread queue

[Christoph Hellwig <hch@lst.de>]

On Sun, Jun 20, 2010 at 11:40:58AM +0300, Artem Bityutskiy wrote:
> Christoph, thanks for simplifying this. I wonder also, why do we need
> the bdi_pending_list - for me it looks redundant.
> 
> Also, do we need the forker task? It hurts because it wakes up every 5
> sec jut to check whether it has to fork something and to waste the
> battery energy. Do we really need to bdi threads to kill themselves
> after 5 minutes of inactivity?

I don't like the design very much either.  I think the problem is that
we currently don't have an interface to tell whether a bdi is actually
used for a filesystem.  We only need the flusher thread any filesystem
is using a bdi currently.  I've started looking a this, but it's not
that easy.  First I need to sort out the current bdi_init/register/
unregister/destroy interface which has grown organicly and currenly
isn't exacly symmetric.  After that I can look into a new interface
to start/stop the thread on an otherwise fully set up bdi, which should
allow getting rid of the forker and it's complications.