On Tue, Nov 21, 2023 at 09:06:18AM -0500, Mathieu Desnoyers wrote: > Task trace RCU fits a niche that has the following set of requirements/tradeoffs: > > - Allow page faults within RCU read-side (like SRCU), > - Has a low-overhead read lock-unlock (without the memory barrier overhead of SRCU), > - The tradeoff: Has a rather slow synchronize_rcu(), but tracers should not care about > that. Hence, this is not meant to be a generic replacement for SRCU. > > Based on my reading of https://lwn.net/Articles/253651/ , preemptible RCU is not a good > fit for the following reasons: > > - It disallows blocking within a RCU read-side on non-CONFIG_PREEMPT kernels, Your counter points are confused, we simply don't build preemptible RCU unless PREEMPT=y, but that could surely be fixed and exposed as a separate flavour. > - AFAIU the mmap_sem used within the page fault handler does not have priority inheritance. What's that got to do with anything? Still utterly confused about what task-tracing rcu is and how it is different from preemptible rcu.
