[LU-12092] Reduce round trip for PFL component instantiation

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Assignee: Patrick Farrell (Inactive)
• Reporter: Patrick Farrell (Inactive)

Description

Currently, when a client sends a write intent to the server to instantiate a new layout component, the server handles the write intent and grants an EX lock on the layout to the client.  The client restarts its i/o and then calls ll_refresh_layout to get the updated layout.  Refresh layout does not look for EX locks, so the client requests a new lock from the server, which cancels its own EX lock before granting the new lock, generating multiple extra round trips.

This is unnecessary - the client can use the EX lock to refresh the layout.  The lock will be cancelled by another client when needed.

A tiny local benchmark of writing 1K in to a new PFL component suggests this reduces the time to instantiate by 50% (comparison is already instantiated file vs PFL instantiation vs PFL instantiation + patch), and overall time for this 1K write by ~10%.