[dm-devel] RFC for multipath queue_if_no_path timeout.

[Alasdair G Kergon]

But this still dodges the fundamental problem:

  What is the right value to use for the timeout?
  - How long should you wait for a path to (re)appear?
    - In the current model, reinstating a path is a userspace 
      responsibility.

The timeout, as proposed, is being used in two conflicting ways:
  - How long to wait for path recovery when all paths went down
  - How long to wait when the system locks without enough free
    memory even to reinstate a path (because of broken userspace
    code) before having multipath fail queued I/O in a desperate
    attempt at releasing memory to assist recovery
 
The second case should point to a very short timeout.
The first case probably wants a longer one.

In my view the correct approach for the case Frank is discussing is to
use a different trigger to detect the (approaching?) locking up of the
system.   E.g.  should something related to the handling of an out
of memory condition have a hook to instruct multipath to release such
queued I/O?

Alasdair