From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2] Driver for Inter-VM shared memory device for KVM supporting interrupts. Date: Wed, 20 May 2009 11:45:50 +0300 Message-ID: <4A13C33E.3090705@redhat.com> References: <1241713567-17256-1-git-send-email-cam@cs.ualberta.ca> <4A12E37C.700@cs.ualberta.ca> <200905201228.38718.rusty@rustcorp.com.au> <200905200933.01736.borntraeger@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Rusty Russell , Cam Macdonell , kvm@vger.kernel.org, Christian Ehrhardt , Anthony Liguori To: =?UTF-8?B?Q2hyaXN0aWFuIEJvcm50csOkZ2Vy?= Return-path: Received: from mx2.redhat.com ([66.187.237.31]:44763 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755658AbZETIqD (ORCPT ); Wed, 20 May 2009 04:46:03 -0400 In-Reply-To: <200905200933.01736.borntraeger@de.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Christian Borntr=C3=A4ger wrote: > o shared guest kernels: The CMS operating system is build as a bootab= le DCSS > (called named-saved-segments NSS). All guests have the same host pa= ges for > the read-only parts of the CMS kernel. The local data is stored in > exclusive-write parts of the same NSS. Linux on System z is also ca= pable of > using this feature (CONFIG_SHARED_KERNEL). The kernel linkage is ch= anged in > a way to separate the read-only text segment from the other parts w= ith > segment size alignment > =20 How does patching (smp, kprobes/jprobes, markers/ftrace) work with this= ? > o execute-in-place: This is a Linux feature to exploit the DCSS techn= ology. > The goal is to shared identical guest pages without the additional = overhead > of KSM etc. We have a block device driver for DCSS. This block devi= ce driver > supports the direct_access function and therefore allows to use the= xip > option of ext2. The idea is to put binaries into an read-only ext2 > filesystem. Whenever an mmap is made on this file system, the page = is not > mapped into the page cache. The ptes point into the DCSS memory ins= tead. > Since the DCSS is demand-paged by the host no memory is wasted for = unused > parts of the binaries. In case of COW the page is copied as usual. = It turned > out that installations with many similar guests (lets say 400 guest= s) will > profit in terms of memory saving and quicker application startups (= not the > first guest of course). There is a downside: this requires a skille= d > administrator to setup. ksm might be easier to admin, at the cost of some cpu time. --=20 error compiling committee.c: too many arguments to function