Re: [PATCH RFC] mm: Implement balance_dirty_pages() through waiting for flusher thread

[Jan Kara <jack@suse.cz>]

On Tue 22-06-10 10:31:24, Christoph Hellwig wrote:
> On Tue, Jun 22, 2010 at 09:52:34PM +0800, Wu Fengguang wrote:
> > 2) most writeback will be submitted by one per-bdi-flusher, so no worry
> >    of cache bouncing (this also means the per CPU counter error is
> >    normally bounded by the batch size)
> 
> What counter are we talking about exactly?  Once balanance_dirty_pages
  The new per-bdi counter I'd like to introduce.

> stops submitting I/O the per-bdi flusher thread will in fact be
> the only thing submitting writeback, unless you count direct invocations
> of writeback_single_inode.
  Yes, I agree that the per-bdi flusher thread should be the only thread
submitting lots of IO (there is direct reclaim or kswapd if we change
direct reclaim but those should be negligible). So does this mean that
also I/O completions will be local to the CPU running per-bdi flusher
thread? Because the counter is incremented from the I/O completion
callback.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR