linux-kernel - Re: [patch] my mmu notifiers

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Message-ID: <20080220024602.GA11364@sgi.com>
Date:	Tue, 19 Feb 2008 20:46:03 -0600
From:	Robin Holt <holt@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Nick Piggin <npiggin@...e.de>, Jack Steiner <steiner@....com>,
	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>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Christoph Lameter <clameter@....com>
Subject: Re: [patch] my mmu notifiers

On Wed, Feb 20, 2008 at 01:52:06AM +0100, Andrea Arcangeli wrote:
> On Wed, Feb 20, 2008 at 12:04:27AM +0100, Nick Piggin wrote:
> > OK (thanks to Robin as well). Now I understand why you are using it,
> > but I don't understand why you don't defer new TLBs after the point
> > where the linux pte changes. If you can do that, then you look and
> > act much more like a TLB from the point of view of the Linux vm.
> 
> Christoph was forced to put the invalidate_range callback _after_
> dropping the PT lock because xpmem has to wait I/O there. But
> invalidate_range is called after freeing the VM reference on the pages
> so then GRU needed a _range_begin too because GRU has to flush the tlb
> before the VM reference on the page is released (xpmem and KVM pin the
> pages mapped by the secondary mmu, GRU doesn't). So then
> invalidate_range was renamed to invalidate_range_end.

Currently, xpmem blocks faults for the range specified at the _begin
callout, then shoots down remote TLBs and does the put_page for all the
pages in the specified range.  The _end callout merely removes the block.
We do not do any wait for I/O.  By the time we return from the _begin
callout, all activity by the remotes is stopped, pages are dereferenced,
and future faults are blocked until released by the _end callout.

Thanks,
Robin
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