linux-kernel - Re: [v2.6.26] what's brewing in x86.git for v2.6.26

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Date:	Thu, 17 Apr 2008 20:47:06 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [v2.6.26] what's brewing in x86.git for v2.6.26

On Thu, Apr 17, 2008 at 11:36 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Thu, 17 Apr 2008 11:30:25 +0200 Ingo Molnar <mingo@...e.hu> wrote:
>  > you mean kmemcheck? Yes, that's planned. We've been working 4 months
>  > non-stop on kmemcheck to make it mergeable and usable, it's at version 7
>  > right now, and it caught a handful of real bugs already (such as
>  > 63a7138671c - unfortunately not credited in the log to kmemcheck). But
>  > because it touches SLUB (because it has to - and they are acked by
>  > Pekka) i never had the chance to move it into the for-akpm branch.
>
>  Does it really really really need to consume one of our few remaining page
>  flags?  We'll be in a mess when we run out.

Actually it doesn't. I attach a patch which gets rid of the page flag,
and we rely instead on the PTE flag for page-trackedness.

The reason we didn't do this at once is that the making of kmemcheck
has been pretty much my first introduction to SLUB, x86, page flags,
etc., and the actual semantics of the various introduced flags have
varied since the first version of kmemcheck. At this point, the struct
page flags weren't actually needed anymore, but they were convenient.

My apologies for not inlining the patch -- I don't have a mail client
that won't mess up whitespace. It can also be downloaded at:
http://folk.uio.no/vegardno/linux/0001-kmemcheck-remove-use-of-tracked-page-flag.patch

The patch has received minimal amount of testing, but I've
double-checked the logic. It boots fine on my laptop, boot log at:
http://folk.uio.no/vegardno/linux/kmemcheck-20080417.txt

Ingo, will you take this for some additional testing?

Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036

View attachment "0001-kmemcheck-remove-use-of-tracked-page-flag.patch" of type "text/x-patch" (7036 bytes)