[LU-8047] optimize ll_md_blocking_ast() for a failed lock

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.13.0, Lustre 2.12.3
• Affects Version/s: Lustre 2.9.0
• Labels: patch
• Severity: 3
• Assignee: Andrew Perepechko
• Reporter: Andrew Perepechko

Description

When investigating performance issues with LU-4398, we've found that if the MDS does not return a lock for an open request, ll_md_blocking_ast() will be called for a failed UPDATE lock on the corresponding directory. ll_invalidate_negative_children() will process the whole cache associated with the directory in order to find negative entries and invalidate them.

If a directory has millions of cached dentries, ll_invalidate_negative_children() spends several scheduler ticks just to process the list. There is clearly some room for ll_invalidate_negative_children() optimization, but we'd like to optimize at least ll_md_blocking_ast() to avoid processing for not granted locks.

A patch will be uploaded shortly.