linux-kernel - Re: [PATCH] VMware Balloon driver

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Date:	Mon, 5 Apr 2010 16:11:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	Avi Kivity <avi@...hat.com>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Dmitry Torokhov <dtor@...are.com>,
	linux-kernel@...r.kernel.org, pv-drivers@...are.com
Subject: Re: [PATCH] VMware Balloon driver

On Mon, 5 Apr 2010 16:03:48 -0700 (PDT)
Dan Magenheimer <dan.magenheimer@...cle.com> wrote:

> > > On 04/06/2010 01:17 AM, Andrew Morton wrote:
> > > >> The basic idea of the driver is to allow a guest system to give up
> > > >> memory it isn't using so it can be reused by other virtual
> > machines (or
> > > >> the host itself).
> > > >>
> > > > So...  does this differ in any fundamental way from what
> > hibernation
> > > > does, via shrink_all_memory()?
> > > >
> > >
> > > Just the _all_ bit, and the fact that we need to report the freed
> > page
> > > numbers to the hypervisor.
> > >
> > 
> > So...  why not tweak that, rather than implementing some parallel
> > thing?
> 
> I think Avi was being facetious ("_all_").  Hibernation assumes
> everything in the machine is going to stop for awhile.  Ballooning
> assumes that the machine has lower memory need for awhile, but
> is otherwise fully operational.

shrink_all_memory() doesn't require that processes be stopped.

If the existing code doesn't exactly match virtualisation's
requirements, it can be changed.

>  Think of it as hot-plug memory
> at a page granularity.

hotplug is different because it targets particular physical pages.  For
this requirement any old page will do.  Preferably one which won't be
needed soon, yes?

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