From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH] KVM simplified virtio balloon driver Date: Thu, 17 Jan 2008 16:59:15 +1100 Message-ID: <200801171659.16370.rusty@rustcorp.com.au> References: <20080114200357.GA18354@dmt> <200801171429.32888.rusty@rustcorp.com.au> <478ED32A.1060803@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm-devel , virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Anthony Liguori Return-path: In-Reply-To: <478ED32A.1060803-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Thursday 17 January 2008 15:01:46 Anthony Liguori wrote: > Rusty Russell wrote: > > OTOH it's currently pretty obvious (and usually fatal) if the guest has > > trouble meeting the balloon requirements. A serious host needs a way of > > detecting stress in the guest anyway, which this doesn't offer until it's > > too late... > > The question I'm interested in answering though is not if but when. I > would like to know when the guest has reached it's target. I'm saying that it will be v. quickly in all but "too much squeeze" case. > And while we do get the madvise call outs, it's possible that pages have > been faulted in since then. But that's exactly what the balloon number *doesn't* tell you. It can tell you that it's released pages back to be used by the OS, but not whether the OS has used them. I think this number is good for debugging the balloon driver, but for anything else it's a false friend. Rusty. PS. Please cut down mails when you reply. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/