From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:53505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S2NXf-0004G8-Kf for qemu-devel@nongnu.org; Tue, 28 Feb 2012 08:56:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S2NXa-0006AQ-Pb for qemu-devel@nongnu.org; Tue, 28 Feb 2012 08:56:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15376) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S2NXa-0006AD-HK for qemu-devel@nongnu.org; Tue, 28 Feb 2012 08:56:30 -0500 Message-ID: <4F4CDD05.5030003@redhat.com> Date: Tue, 28 Feb 2012 15:56:21 +0200 From: Avi Kivity MIME-Version: 1.0 References: <1333613dbb15f2b736394d77e795223e.squirrel@ssl.dlh.net> <2c2e4d6e-53f0-4698-8ad0-f4708b7987c6@email.android.com> <4F4CD3AF.7090709@redhat.com> <4F4CD494.5020909@dlh.net> In-Reply-To: <4F4CD494.5020909@dlh.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] linux guests and ksm performance List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, kvm@vger.kernel.org On 02/28/2012 03:20 PM, Peter Lieven wrote: > On 28.02.2012 14:16, Avi Kivity wrote: >> On 02/24/2012 08:41 AM, Stefan Hajnoczi wrote: >>>> I dont think that it is cpu intense. All user pages are zeroed >>>> anyway, but at allocation time it shouldnt be a big difference in >>>> terms of cpu power. >>> It's easy to find a scenario where eagerly zeroing pages is wasteful. >>> Imagine a process that uses all of physical memory. Once it >>> terminates the system is going to run processes that only use a small >>> set of pages. It's pointless zeroing all those pages if we're not >>> going to use them anymore. >> In the long term, we will use them, except if the guest is completely >> idle. >> >> The scenario in which zeroing is expensive is when the page is refilled >> through DMA. In that case the zeroing was wasted. This is a pretty >> common scenario in pagecache intensive workloads. >> > Avi, what do you think of the proposal to give the guest vm a hint > that the host is running ksm? In that case the administrator > has already chosen that saving physical memory is more important > than performance to him? It makes some sense. Perhaps through the balloon device, a flag that indicates that voluntary ballooning will be gratefully accepted. -- error compiling committee.c: too many arguments to function