linux-kernel - Re: [PATCH v2 1/5] sched, timer: Remove usages of ACCESS

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Message-ID: <20150429131532.15443d08@gandalf.local.home>
Date:	Wed, 29 Apr 2015 13:15:32 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Waiman Long <waiman.long@...com>
Cc:	Jason Low <jason.low2@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v2 1/5] sched, timer: Remove usages of ACCESS_ONCE in
 the scheduler

On Wed, 29 Apr 2015 13:05:55 -0400
Waiman Long <waiman.long@...com> wrote:

> >   		goto no_join;
> > @@ -2107,7 +2107,7 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
> >
> >   static void reset_ptenuma_scan(struct task_struct *p)
> >   {
> > -	ACCESS_ONCE(p->mm->numa_scan_seq)++;
> > +	WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
> >   	p->mm->numa_scan_offset = 0;
> >   }
> >
> >
> 
> Generally, I am for replacing ACCESS_ONCE() with the more descriptive 
> READ_ONCE() and WRITE_ONCE() except the above case where it makes the 
> code harder to read without any real advantage.
> 
> Other than that,
> 
> Acked-by: Waiman Long <Waiman.Long@...com>
> 

I agree, but I believe this code needs to be updated anyway. Making it
uglier may encourage that to happen.

-- Steve
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