[ofa-general] Re: [patch 5/6] mmu_notifier: Support for drivers with revers maps (f.e. for XPmem)

Robin Holt
2008-02-20T09:00:36Z

On Wed, Feb 20, 2008 at 02:51:45PM +1100, Nick Piggin wrote:
> On Wednesday 20 February 2008 14:12, Robin Holt wrote:
> > For XPMEM, we do not currently allow file backed
> > mapping pages from being exported so we should never reach this condition.
> > It has been an issue since day 1. We have operated with that assumption
> > for 6 years and have not had issues with that assumption. The user of
> > xpmem is MPT and it controls the communication buffers so it is reasonable
> > to expect this type of behavior.
>
> OK, that makes things simpler.
>
> So why can't you export a device from your xpmem driver, which
> can be mmap()ed to give out "anonymous" memory pages to be used
> for these communication buffers?

Because we need to have heap and stack available as well. MPT does
not control all the communication buffer areas. I haven't checked, but
this is the same problem that IB will have. I believe they are actually
allowing any memory region be accessible, but I am not sure of that.

Thanks,
Robin