linux-kernel - Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig

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Date:	Mon, 7 Aug 2006 19:41:59 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Andi Kleen <ak@...e.de>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Randy.Dunlap" <rdunlap@...otime.net>,
	"Protasevich, Natalie" <Natalie.Protasevich@...sys.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: Make NR_IRQS configurable in Kconfig

On Tue, 8 Aug 2006 04:17:59 +0200
Andi Kleen <ak@...e.de> wrote:

> 
> > 
> > And it's a pretty nasty one because it can get people into the situation
> > where the kernel worked fine for those who released it, but users who
> > happen to load more modules (or the right combination of them) will
> > experience per-cpu memory exhaustion.
> 
> Yes, and a high value will waste a lot of memory for normal users.
>  
> > So shouldn't we being scaling the per-cpu memory as well?
> 
> If we move it into vmalloc space it would be easy to extend at runtime - just the
> virtual address space would need to be prereserved, but then more pages
> could be mapped. Maybe we should just do that instead of continuing to kludge around?

Sounds sane.

otoh, we need something for 2.6.19.

> Drawback would be some more TLB misses.

yup.  On some (important) architectures - I'm not sure which architectures
do the bigpage-for-kernel trick.
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