linux-kernel - Re: [PATCH] x86: 46 bit PAE support

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Message-ID: <20090507144904.GA2344@elte.hu>
Date:	Thu, 7 May 2009 16:49:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Pavel Machek <pavel@....cz>, Rik van Riel <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, mingo@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] x86: 46 bit PAE support


* H. Peter Anvin <hpa@...or.com> wrote:

> Ingo Molnar wrote:
> > 
> > Yes, struct page is ~64 bytes, and 64*64 == 4096.
> > 
> > Alas, it's not a problem: my suggestion wasnt to simulate 64 TB of 
> > RAM. My suggestion was to create a sparse physical memory map (in a 
> > virtual machine) that spreads ~1GB of RAM all around the 64 TB 
> > physical address space. That will test whether the kernel is able to 
> > map and work with such physical addresses. (which will cover most of 
> > the issues)
> > 
> > A good look at /debug/x86/dump_pagetables with such a system booted 
> > up would be nice as well - to make sure every virtual memory range 
> > is in its proper area, and that there's enough free space around 
> > them.
> > 
> 
> We're working on simulating this at Intel.  We should hopefully be 
> able to test this next week.

Wow, very nice!

It would be nice to do it on a KVM basis and submit the 
weird-memory-layout submission to the KVM tree. It would be helpful 
with the reproduction of weird, memory layout dependent bugs too for 
example. Plus we could create a test facility that randomizes the 
physical memory layout (with a given fragmentation level).

	Ingo
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