Re: [PATCH v2 00/35] Speculative page faults

[Michel Lespinasse]

On Tue, Feb 01, 2022 at 02:20:39AM +0000, Matthew Wilcox wrote:
> On Mon, Jan 31, 2022 at 05:14:34PM -0800, Andrew Morton wrote:
> > On Fri, 28 Jan 2022 05:09:31 -0800 Michel Lespinasse <michel@xxxxxxxxxxxxxx> wrote:
> > > The next step is to walk down the existing page table tree to find the
> > > current pte entry. This is done with interrupts disabled to avoid
> > > races with munmap().
> > 
> > Sebastian, could you please comment on this from the CONFIG_PREEMPT_RT
> > point of view?
> 
> I am not a fan of this approach.  For other reasons, I think we want to
> switch to RCU-freed page tables, and then we can walk the page tables
> with the RCU lock held.  Some architectures already RCU-free the page
> tables, so I think it's just a matter of converting the rest.

Note - I have no problem with switching to RCU-freed page tables
everywhere when and if we end up needing to. I just don't see that
this need comes from the SPF patchset, so I don't think this should
be introduced as an artificial dependency.

--
Michel "walken" Lespinasse