From: Thomas Fjellstrom <tfjellstrom@shaw.ca>
Subject: Re: Memory under KVM?
Date: Wed, 16 Dec 2009 02:58:43 -0700
Message-ID: <200912160258.43761.tfjellstrom@shaw.ca>
References: <4B22BCE5.7040208@binaryfreedom.info> <200912151621.19082.tfjellstrom@shaw.ca> <4B28AE8D.6080600@redhat.com>
Reply-To: tfjellstrom@shaw.ca
Mime-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Cc: kvm@vger.kernel.org
To: Avi Kivity <avi@redhat.com>
In-Reply-To: <4B28AE8D.6080600@redhat.com>
Sender: kvm-owner@vger.kernel.org

On Wed December 16 2009, Avi Kivity wrote:
> On 12/16/2009 01:21 AM, Thomas Fjellstrom wrote:
> >>> The problem is it should be automatic. The balloon driver itself or
> >>> some other mechanism should be capable of noticing when it can free
> >>> up a bunch of guest memory. I can't be bothered to manually sit
> >>> around and monitor memory usage on my host so I can then go into
> >>> virt-manager to reduce memory to each guest.
> >>
> >> That should be pretty easy though it will have an effect on guest
> >> performance.
> >
> > As long as its only done after an appropriately long idle period (ie:
> > theres been X MB's free for a long time, give it back), I can't see it
> > harming performance too much. At least not more than setting ram too
> > low when manually (de)ballooning memory.
> 
> It depends on what your expectations are.  If you have a lot of memory
> you might be surprised when you access an idle guest and have to wait
> for it to page itself back from disk.
> 

Why would it be swaping in that case? Only unused/free/cache memory should 
be returned to the host.

-- 
Thomas Fjellstrom
tfjellstrom@shaw.ca