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Date: Thu, 17 Apr 2008 03:33:33 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Pekka Enberg" <penberg@cs.helsinki.fi>
Cc: "Ingo Molnar" <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       "Linus Torvalds" <torvalds@linux-foundation.org>,
       "Thomas Gleixner" <tglx@linutronix.de>,
       "H. Peter Anvin" <hpa@zytor.com>,
       "Vegard Nossum" <vegard.nossum@gmail.com>
Subject: Re: [v2.6.26] what's brewing in x86.git for v2.6.26
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On Thu, 17 Apr 2008 13:19:32 +0300 "Pekka Enberg" <penberg@cs.helsinki.fi> wrote:

> On Thu, Apr 17, 2008 at 12:36 PM, Andrew Morton
> <akpm@linux-foundation.org> 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.
> 
> FYI, the initial version of kmemcheck didn't have a separate page flag
> (it abused SLUB internals) but it got really hairy and I think I
> finally convinced Vegard to switch over to page flags after some
> hair-pulling when we hit a bug. So yes, from SLUB maintainer point of
> view, we _really, really_ want to use a page flag here.

Thank you whoever wrote kmemcheck.txt

How come slub uses one byte to track the status of each byte when it could
use a single bit?

We (still!) have not made the decision whether to proceed with slab or
slub.  How hard would it be to port kmemcheck into slab?