On Tue, Apr 06, 2021 at 06:44:59PM -0700, Michel Lespinasse wrote: > Performance tuning: as single threaded userspace does not use > speculative page faults, it does not require rcu safe vma freeing. > Turn this off to avoid the related (small) extra overheads. > > For multi threaded userspace, we often see a performance benefit from > the rcu safe vma freeing - even in tests that do not have any frequent > concurrent page faults ! This is because rcu safe vma freeing prevents > recently released vmas from being immediately reused in a new thread.
Why does that provide a performance benefit? Recently released VMAs are cache-hot, and NUMA-local. I'd expect the RCU delay to be performance-negative.
