linux-kernel - Re: [patch 3/9] Guest page hinting: volatile page cache.

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Date:	Thu, 14 Sep 2006 02:23:38 -0700
From:	Zachary Amsden <zach@...are.com>
To:	schwidefsky@...ibm.com
Cc:	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	akpm@...l.org, nickpiggin@...oo.com.au, frankeh@...son.ibm.com,
	rhim@...gateh.edu
Subject: Re: [patch 3/9] Guest page hinting: volatile page cache.

Martin Schwidefsky wrote
> The discard fault happens on access to a volatile that has been
> discarded. An important property of the s390 architecture comes into
> play here: there are two page tables, a guest page table and a host page
> table. What the guest perceives as its "physical" memory is in virtual
> storage for the host. An address resolution has to walk two pages
> tables, if a pte is invalid in either table you get a fault. A guest
> fault if the invalid pte is in the guest table and a host fault if it is
>   

Yes, I'm familiar with that trick.  Wasn't sure if you had it in 
hardware or not.

> in the host table. That gives s390 a simple method to implement
> discarded pages: the hypervisor just unmaps the page from the host table
> and changes the state of the guest page. I can see that you will have a
> much harder time to implement this on i386.
>   

Nah, I think we'll do just fine.

Thanks for the info - based on this, I think we can probably use the 
volatile page / swap cache changes as well for VMware, also pretty much 
unchanged.  Sorry to take so long to look at these patches, BTW - I was 
on holiday for two weeks.

Zach
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