Re: [PATCH 10/17] prmem: documentation

[Peter Zijlstra]

On Wed, Oct 31, 2018 at 03:57:21PM -0700, Andy Lutomirski wrote:
> > On Oct 31, 2018, at 2:00 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >> On Wed, Oct 31, 2018 at 01:36:48PM -0700, Andy Lutomirski wrote:

> >> This stuff is called *rare* write for a reason. Do we really want to
> >> allow atomics beyond just store-release?  Taking a big lock and then
> >> writing in the right order should cover everything, no?
> > 
> > Ah, so no. That naming is very misleading.
> > 
> > We modify page-tables a _lot_. The point is that only a few sanctioned
> > sites are allowed writing to it, not everybody.
> > 
> > I _think_ the use-case for atomics is updating the reference counts of
> > objects that are in this write-rare domain. But I'm not entirely clear
> > on that myself either. I just really want to avoid duplicating that
> > stuff.
> 
> Sounds nuts. Doing a rare-write is many hundreds of cycles at best.

Yes, which is why I'm somewhat sceptical of the whole endeavour.