linux-kernel - Re: [PATCH 0/5] x86: another attempt at x86 pagetable unification

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Message-ID: <20071220213906.GB11897@elte.hu>
Date:	Thu, 20 Dec 2007 22:39:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	Jan Beulich <jbeulich@...ell.com>
Subject: Re: [PATCH 0/5] x86: another attempt at x86 pagetable unification

* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> > found a couple of bugs.
> >
> > firstly, 64-bit wasnt so lucky, you broke 
> > iounmap()/change_page_attr()
> > :-)
> 
> Crap.  Worked for me.  I'll look into it.

well, there's an easy solution for unification patches: the resulting 
object files must have _exactly the same_ content as without the 
unification patches. (Modulo strings as WARN_ON()s referring to 
include-file names.)

If they differ then the unification did something wrong. With your 
patchset and the config i sent, the difference is visible in the image 
size already:

   text     data   bss     dec              hex    filename
   7763766  967330 5812328 14543424         ddea40 vmlinux.after
   7763811  967330 5812328 14543469         ddea6d vmlinux.before

also, reducing the size and scope of changes helps as well - because 
that way it can be bisected down to specific changes. Mistakes 
inevitably happen, especially if you do not enforce a rigid 
byte-for-byte correctness along the way. You did 5 rather large patches, 
and it's not testable because your unification steps were too coarse.

In other words: you were asking for trouble and you got it :-)

	Ingo
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