Filesystem cache improvement: reuse cache priority iterator

Why it matters

This enhancement optimizes cache management by allowing multiple threads to share the cache priority iterator, reducing overhead and improving concurrency when reserving cache space. It helps in better resource utilization and potentially increases performance by minimizing contention in cache operations.

How to use it

This improvement is integrated internally and does not require explicit user configuration. Users benefit automatically from enhanced filesystem cache behavior when upgrading to the version including this change.