linux-kernel - Re: [RFC patch] introduce sys_membarrier(): process-wide memory barrier (v9)

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Date:	Mon, 22 Feb 2010 16:23:21 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...e.hu,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [RFC patch] introduce sys_membarrier(): process-wide memory
	barrier (v9)

* Chris Friesen (cfriesen@...tel.com) wrote:
> On 02/12/2010 04:46 PM, Mathieu Desnoyers wrote:
> 
> > Editorial question: 
> > 
> > This synchronization only takes care of threads using the current process memory
> > map. It should not be used to synchronize accesses performed on memory maps
> > shared between different processes. Is that a limitation we can live with ?
> 
> It makes sense for an initial version.  It would be unfortunate if this
> were a permanent limitation, since using separate processes with
> explicit shared memory is a useful way to mitigate memory trampler issues.
> 
> If we were going to allow that, it might make sense to add an address
> range such that only those processes which have mapped that range would
> execute the barrier.  Come to think of it, it might be possible to use
> this somehow to avoid having to execute the barrier on *all* threads
> within a process.

The extensible system call mandatory and optional flags will allow this kind of
improvement later on if this appears to be needed. It will also allow user-space
to detect if later kernels support these new features or not. But meanwhile I
think it's good to start with this implementation that covers 99.99% of
use-cases I can currently think of (ok, well, maybe I'm just unimaginative) ;)

Thanks,

Mathieu

> 
> Chris
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