Re: bdi forker

[Christoph Hellwig <hch@infradead.org>]

> I was looking at the code and and found it to bee more complex that it
> has to be. I'd suggest to:
> 
> 1. Stop exiting per-bdi flushers after 5 minutes of inactivity.
> 2. Kill the forker thread and make the default bdi us the same flusher
> thread as every other bdi uses.
> 
> This will simplify many things, I believe. Various lists and locks and
> will go away, the code will become more readable.

They do.  I've actually implemented this and it simplifies the code a
lot.  But there's one big downside:  We now create a thread for every
block device, even if it's not used.  For a normal systems that's fine,
but on a system connected to a larger SAN this migh be quite a bit of
overhead.  Then again systems connected to a large SAN can usually deal
with the overhead.  I'm planning into just activating the thread if
a filesystems in mounted on the BDI, which should be just as a good as
the lazy startup/teardown.

I'll send out the preliminary series this week so that you can take a
look.