linux-kernel - Re: [PATCH 1/2] mm: implement remap_pfn_range with apply_to_page

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Date:	Mon, 17 Nov 2008 14:03:04 +1100
From:	Peter Chubb <peterc@...ato.unsw.edu.au>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Subject: Re: [PATCH 1/2] mm: implement remap_pfn_range with apply_to_page_range

>>>>> "Nick" == Nick Piggin <nickpiggin@...oo.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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