[LU-11000] Retain cached dentries under directory update lock

• Type: Improvement
• Resolution: Unresolved
• Priority: Major
• Assignee: WC Triage
• Reporter: Oleg Drokin

Description

In line with LU-10999 we should be able to retain directory entries in cache on the clients even without update locks assuming we have UPDATE lock on the parent directory.

Currently this mostly affects various opens that are routinely answered without any LOOKUP bit set.

We already have the code that iterates all the children when a directory UPDATE lock is canceled in search of negative dentries, so we can use that to also prune all such lockless dentries too.

Issue Links

• is related to: LU-17329 Relaxed POSIX Consistency for Lustre
• is related to: LU-3308 large readdir chunk size slows unlink/"rm -r" performance
• is related to: LU-10999 Use readdir cache for lookup when available