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

[Ingo Molnar <mingo@elte.hu>]

* 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.

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