On Fri, Aug 12, 2011 at 12:21:44PM -0600, Bruce Guenter wrote:

On Thu, Aug 11, 2011 at 05:40:36PM -0700, Simon Kirby wrote:

quoted

By chance, does "vmstat 1" or top show a high system cpu% while this is
happening,

Absolutely, usually around 80-90%

...which is perhaps why you had difficult obtaining traces with sysrq-w,
since most of the time there were no D-state processes. Instead, sysrq-l
give a backtrace of each running CPU.

quoted

and if so, does cat /proc/<pid>/stack of the PIDs in R state
sometimes show things under btrfs_run_delayed_refs like
setup_cluster_no_bitmap() and rb_next()?

No, I am not seeing what you describe.  The stack traces are usually
showing what I originally quoted.  I don't know if I've seen
setup_cluster_no_bitmap or rb_* at all.

Ok, oh well. :)

Simon-