Date: Thu, 1 Nov 2018 18:08:09 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Andy Lutomirski <luto@...capital.net> Cc: Matthew Wilcox <willy@...radead.org>, Igor Stoppa <igor.stoppa@...il.com>, Tycho Andersen <tycho@...ho.ws>, Kees Cook <keescook@...omium.org>, Mimi Zohar <zohar@...ux.vnet.ibm.com>, Dave Chinner <david@...morbit.com>, James Morris <jmorris@...ei.org>, Michal Hocko <mhocko@...nel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-integrity <linux-integrity@...r.kernel.org>, LSM List <linux-security-module@...r.kernel.org>, Igor Stoppa <igor.stoppa@...wei.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Jonathan Corbet <corbet@....net>, Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Mike Rapoport <rppt@...ux.vnet.ibm.com>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 10/17] prmem: documentation On Wed, Oct 31, 2018 at 03:57:21PM -0700, Andy Lutomirski wrote: > > On Oct 31, 2018, at 2:00 PM, Peter Zijlstra <peterz@...radead.org> 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.
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