linux-kernel - Re: [RFC PATCH 11/15] memremap: Add zone device access protection

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Message-ID: <20200714194031.GI5523@worktop.programming.kicks-ass.net>
Date:   Tue, 14 Jul 2020 21:40:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 11/15] memremap: Add zone device access protection

On Tue, Jul 14, 2020 at 12:10:47PM -0700, Ira Weiny wrote:
> On Tue, Jul 14, 2020 at 10:40:57AM +0200, Peter Zijlstra wrote:

> > That's an anti-pattern vs static_keys, I'm thinking you actually want
> > static_key_slow_{inc,dec}() instead of {enable,disable}().
> 
> Thanks.  I'll go read the doc for those as I'm not familiar with them.

Look for static_branch_{inc,dec} in include/linux/jump_label.h, it
basically does the refcount thing you need and does the actual
transition on the 0->1 and 1->0 transitions.