Subject: Re: sparse, kernel-only crashdumps
To: David Young <dyoung@pobox.com>
From: Jason Thorpe <thorpej@shagadelic.org>
List: tech-kern
Date: 10/07/2004 09:16:29
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On Oct 6, 2004, at 11:39 PM, David Young wrote:

> It looks to me like it isn't too hard to make a sparse crashdump on x86
> that contains only the pages that are mapped into kernel virtual 
> memory,
> the page directory and page table pages (PDP and PTPs).  Does a 
> crashdump
> require any other pages?  I have a need for compact crashdumps, so I am
> going to work on this over the weekend.

If you want to make this generic, you need to figure out how to account 
for direct-mapped segments, like the ones MIPS, Alpha, VAX, and SH 
have, as well as the way BATs are used on PowerPC.  Those regions are 
used by the kernel, but not managed by the VM system.  They are often 
used for pool pages, and sometimes for other data structures used by 
low-level VM code (see the Alpha pmap, for example).  All of that stuff 
would need to be dumped, too.

I'm not inclined to support a solution that does not address the whole 
problem.

         -- Jason R. Thorpe <thorpej@shagadelic.org>


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