From mboxrd@z Thu Jan  1 00:00:00 1970
From: Robin Holt <holt@sgi.com>
Subject: [ofa-general] Re: [PATCH 08 of 11] anon-vma-rwsem
Date: Tue, 13 May 2008 10:32:38 -0500
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Cc: Avi Kivity <avi@qumranet.com>, linux-mm@kvack.org,
	Hugh Dickins <hugh@veritas.com>, Nick Piggin <npiggin@suse.de>,
	kvm-devel@lists.sourceforge.net, Roland Dreier <rdreier@cisco.com>,
	Eric Dumazet <dada1@cosmosbay.com>, general@lists.openfabrics.org,
	Christoph Lameter <clameter@sgi.com>, Jack Steiner <steiner@sgi.com>,
	Andrea Arcangeli <andrea@qumranet.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Rusty Russell <rusty@rustcorp.com.au>, Chris Wright <chrisw@redhat.com>,
	Anthony Liguori <aliguori@us.ibm.com>, Marcelo Tosatti <marcelo@kvack.org>,
	Kanoj Sarcar <kanojsarcar@yahoo.com>, linux-kernel@vger.kernel.org,
	"Paul E. McKenney" <paulmck@us.ibm.com>, Robin Holt <holt@sgi.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
To: Nick Piggin <nickpiggin@yahoo.com.au>
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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