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

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Message-ID: <20080417094606.GA19607@elte.hu>
Date:	Thu, 17 Apr 2008 11:46:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	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

* Andrew Morton <akpm@...ux-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.

well AFAICS the shortage really mostly affects 32-bit platforms. And 
there we've got 19 bits used, out of 23 available, right?

whether we track a page or not is rather fundamental to kmemcheck, i 
dont see any easy way to get rid of that usage. (and since kmemcheck is 
a transparent add-on, i dont see any obvious other candidate like 
page->private either - all those fields might be utilized)

if we run out of that in the future: the high bits get used by sparse 
section and numa node ID bits, worst-case we could live with restricting 
the max number of NUMA nodes on 32-bit from 64 to 32? [NUMA on 32-bit is 
an afterthought anyway.] Or we could do a CONFIG_KMEMCHECK=y only 
page->flags_debug.

	Ingo
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