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Message-ID: <20181101170809.GG3178@hirez.programming.kicks-ass.net>
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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