[sheepdog] [PATCH] sheep: introduce 'short thread' to worker threads

[Christoph Hellwig]

Sorry for being late to the discussion, but creating a new thread for
every queued work item is a massive scalability problem.  I don't mind
growing / shrinking the pool dynamically, but having to create a thread
for every single request is going to hit the kernel really hard.

We'll at least need to keep a pool of available threads around.