Re: [RFC PATCH 00/10] RCU: Enable callbacks to benefit from expedited grace periods

[Puranjay Mohan]

Hi Frederic,

Thanks a lot for the detailed feedback on all patches, I will send the
next version soon with requested changes.


On Thu, May 28, 2026 at 1:14 PM Frederic Weisbecker <frederic@xxxxxxxxxx> wrote:
>
> Hi,
>
> Le Fri, Apr 17, 2026 at 04:11:48PM -0700, Puranjay Mohan a écrit :
> > RCU callbacks only track normal grace period sequence numbers. This
> > means callbacks must wait for normal GPs even when expedited GPs have
> > already elapsed.
> >
> > This series tracks both normal and expedited GP sequences in the
> > callback infrastructure using struct rcu_gp_oldstate, so callbacks
> > advance when either GP type completes.
>
> What is the motivation behind this? When most callbacks don't have much latency
> requirements between queue and invocation?

Right now there's an asymmetry: synchronize_rcu_expedited() callers
get fast object freeing, but call_rcu() callers never benefit from
those same grace periods even though they prove the exact same thing.
This series closes that gap, the callback infrastructure treats a
grace period as a grace period regardless of how it was driven. The
practical effect is faster memory reclaim: objects that could already
be safely freed stop sitting around waiting for the next normal GP.
I'll make this motivation clearer in the next version.

Thanks,
Puranjay