Date: Mon, 17 Nov 2008 14:03:04 +1100
Message-ID: <87skpryryv.wl%peter@chubb.wattle.id.au>
From: Peter Chubb <peterc@gelato.unsw.edu.au>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Memory Management List <linux-mm@kvack.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
In-Reply-To: <200811141835.17073.nickpiggin@yahoo.com.au>
References: <491C61B1.10005@goop.org>
	<200811141417.35724.nickpiggin@yahoo.com.au>
	<491D0B2F.7050900@goop.org>
	<200811141835.17073.nickpiggin@yahoo.com.au>
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Subject: Re: [PATCH 1/2] mm: implement remap_pfn_range with apply_to_page_range
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>>>>> "Nick" == Nick Piggin <nickpiggin@yahoo.com.au> writes:


Nick> It's not meant to be pluggable. Actually this came up last I
Nick> think when the UNSW wanted to add page table accessors to
Nick> abstract this.  They came up with a good set of things, but in
Nick> the end you can't justify slowing things down in these paths
Nick> unless you actually have a replacement page table structure that
Nick> gets you a *net win*. So far, I haven't heard from them again.

We tried hard.  The slowdown wasn't all that much on system
benchmarks, but you could see it on the microbenchmarks.  And it made
stuff a LOT cleaner.

We wanted it to put super-page friendly pagetables in for
architectures not wedded to the 3/4 level x86 pagetable hardware
format. 

The people I had working on this left (finished a masters,
finished a PhD, contract ran out and no more money), and I haven't had
the manpower to maintain the patchset, especially after the negative
responses we got from linux-MM.

--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia

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