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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

* Chris Friesen (cfriesen@nortel.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