Re: Hot rb_next, setup_cluster_no_bitmap

Chris Mason
2011-08-04T01:13:26Z

Excerpts from Simon Kirby''s message of 2011-08-03 19:10:59
-0400:
> On Wed, Aug 03, 2011 at 03:39:49PM -0700, Simon Kirby wrote:
>
> > On Wed, Aug 03, 2011 at 03:06:55PM -0700, Simon Kirby wrote:
> >
> > > I see Josef''s 86d4a77ba3dc4ace238a0556541a41df2bd71d49
introduced the
> > > bitmaps list. I could try temporarily reverting this (some fixups
needed)
> > > if anybody thinks my cache bouncing idea might be slightly
possible.
> >
> > I''ll try the attached and see how the profile changes.
>
> Hmm, I bound the SMP affinity of all of the btrfs processes to one CPU,
> and the page dirtying rate got slower, so I suspect the writes
aren''t
> really a big deal, and the problem is just that there is way too much
> walking going on after rsync has ran for a while and loads everything
> into memory.
>
> Any ideas?

The current for-linus branch gets rid of all the bottlenecks in the
metadata blocks.  So now we''re stuck with the bottlenecks in the
allocator.

There are a few simple things we can do here but Josef has a patch that
fixes delalloc reservations for inline extents that might help as a
first step.

-chris