high load and xfsaild in d

[Dave Chinner]

On Thu, Nov 22, 2012 at 06:13:48PM -0800, Keith Keller wrote:
> Hello all,
> 
> I recently deployed a new CentOS 6.3 file server, and soon after I
> noticed that the load was consistenly at around 4, even with no obvious
> activity.  After checking around a bit, the only unusual thing I could
> find is that the xfsaild threads are all consistently in D state:
> 
> root      1744  0.0  0.0      0     0 ?        D    Nov16   7:46 [xfsaild/dm-2]
> root      1756  0.0  0.0      0     0 ?        D    Nov16   7:44 [xfsaild/dm-1]
> root      1759  0.0  0.0      0     0 ?        D    Nov16   7:57 [xfsaild/dm-3]
> root      1762  0.0  0.0      0     0 ?        D    Nov16   5:59 [xfsaild/dm-0]

That's a side effect of a minimal set of bug fixes that were needed
to avoid a load related log space hang. Those fixes disabled the
aild idling logic so the aild acts as a watchdog, so they wake up
every 50ms to check if there's anything to do. You'll find that
3.0.x stable kernels have the same behaviour.

The aild idling logic was re-enabled in mainstream kernels after the
root cause of the log space hangs was diagnosed and fixed, but I
can't see it ever being re-enabled in a CentOS 6.3 kernel....

Cheers,

Dave
-- 
Dave Chinner
david at fromorbit.com