This makes tmpfs more scalable but I want to point out something larger.
This demonstrates a highly scalable pattern that could be applied to all memory resident I/O. It has long been my intention to relegate the buffer cache to an increasingly narrow set of uses due to the legacy design and the scalability issues with lockmgr and exclusive buf locks.
After the introduction of a stronger busy guarantee and lockfree lookup, we can permit file I/O that only contends at the page level. You could eventually even avoid the shared vnode lock when reading cached data.