linux-kernel - Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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Message-ID: <20080229131302.GT8091@v2.random>
Date:	Fri, 29 Feb 2008 14:13:02 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, akpm@...ux-foundation.org,
	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address
	ranges

On Thu, Feb 28, 2008 at 04:59:59PM -0800, Christoph Lameter wrote:
> And thus the device driver may stop receiving data on a UP system? It will 
> never get the ack.

Not sure to follow, sorry.

My idea was:

   post the invalidate in the mmio region of the device
   smp_call_function()
   while (mmio device wait-bitflag is on);

Instead of the current:

   smp_call_function()
   post the invalidate in the mmio region of the device
   while (mmio device wait-bitflag is on);

To decrease the wait loop time.

> invalidate_page_before/end could be realized as an 
> invalidate_range_begin/end on a page sized range?

If we go this route, once you add support to xpmem, you'll have to
make the anon_vma lock a mutex too, that would be fine with me
though. The main reason invalidate_page exists, is to allow you to
leave it as non-sleep-capable even after you make invalidate_range
sleep capable, and to implement the mmu_rmap_notifiers sleep capable
in all the paths that invalidate_page would be called. That was the
strategy you had in your patch. I'll try to drop invalidate_page. I
wonder if then you won't need the mmu_rmap_notifiers anymore.
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