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
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