Re: [kvm-devel] [PATCH 08 of 11] anon-vma-rwsem

[Robin H. <ho...@sg...>]

On Tue, May 13, 2008 at 10:06:44PM +1000, Nick Piggin wrote:
> On Thursday 08 May 2008 10:38, Robin Holt wrote:
> > In order to invalidate the remote page table entries, we need to message
> > (uses XPC) to the remote side.  The remote side needs to acquire the
> > importing process's mmap_sem and call zap_page_range().  Between the
> > messaging and the acquiring a sleeping lock, I would argue this will
> > require sleeping locks in the path prior to the mmu_notifier invalidate_*
> > callouts().
> 
> Why do you need to take mmap_sem in order to shoot down pagetables of
> the process? It would be nice if this can just be done without
> sleeping.

We are trying to shoot down page tables of a different process running
on a different instance of Linux running on Numa-link connected portions
of the same machine.

The messaging is clearly going to require sleeping.  Are you suggesting
we need to rework XPC communications to not require sleeping?  I think
that is going to be impossible since the transfer engine requires a
sleeping context.

Additionally, the call to zap_page_range expects to have the mmap_sem
held.  I suppose we could use something other than zap_page_range and
atomically clear the process page tables.  Doing that will not alleviate
the need to sleep for the messaging to the other partitions.

Thanks,
Robin