linux-kernel - Re: [kvm-devel] [RFC 0/8]KVM: swap out guest pages

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Date:	Tue, 24 Jul 2007 09:10:18 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Avi Kivity <avi@...ranet.com>
Cc:	Shaohua Li <shaohua.li@...el.com>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [kvm-devel] [RFC 0/8]KVM: swap out guest pages

On Mon, 2007-07-23 at 13:27 +0300, Avi Kivity wrote:
> Having an address_space (like your patch does) is remarkably simple, and 
> requires few hooks from the current vm.  However using existing vmas 
> mapped by the user has many advantages:
> 
> - compatible with s390 requirements
> - allows the user to use hugetlbfs pages, which have a performance 
> advantage using ept/npt (but which are unswappable)
> - allows the user to map a file (which can be regarded as way to specify 
> the swap device)
> - better ingration with the rest of the vm

You don't need to expose the vmas.  You just have userspace point out
the start+len of each region of memory it wants the guest to be able to
access, and the address it wants it to appear in the guest.

This is a slight superset of what lguest does in two ways:

1) my guest address == user address, but I'm looking at adding an offset
so I don't have to link the launcher binary specially.
2) I have only one contiguous region of guest-physical memory, since I
can place device memory immediately above "normal" mem.

But the result is pretty sweet, and doesn't require any new symbols to
be exported.

Cheers,
Rusty.

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