[dm-devel] Re: fastfail operation and retries

[Tim Pepper]

On 4/27/05, Lars Marowsky-Bree <lmb at suse.de> wrote:
> User-space needs to take action and tell us when to stop queuing.

Is there any risk of priority inversion?  I can't think of a specific
issue beyond the userspace daemon process simply not existing that
wouldn't hopefully settle out over time and I haven't looked closely
at this aspect of 2.6, but it used to be easy to get/keep the cpu busy
enough on flushing IO to disk to hurt userspace response times (fibre
pulls during heavy buffered, filesystem IO effectively DoSing the
machine for a long period).  If that sort of thing is still possible,
it seems risky relying on a userspace application for
timely/meaningful recovery of the resources consumed by the IO.