From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f180.google.com (mail-pf0-f180.google.com [209.85.192.180]) by kanga.kvack.org (Postfix) with ESMTP id 889AF6B0253 for ; Mon, 7 Mar 2016 00:34:58 -0500 (EST) Received: by mail-pf0-f180.google.com with SMTP id 63so73064517pfe.3 for ; Sun, 06 Mar 2016 21:34:58 -0800 (PST) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTP id 195si26359362pfc.32.2016.03.06.21.34.57 for ; Sun, 06 Mar 2016 21:34:57 -0800 (PST) From: "Li, Liang Z" Subject: RE: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization Date: Mon, 7 Mar 2016 05:34:54 +0000 Message-ID: References: <1457001868-15949-1-git-send-email-liang.z.li@intel.com> <20160303174615.GF2115@work-vm> <20160304081411.GD9100@rkaganb.sw.ru> <20160304102346.GB2479@rkaganb.sw.ru> <56D9B6C2.3070708@redhat.com> <20160304185120.GB2588@work-vm> In-Reply-To: <20160304185120.GB2588@work-vm> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: "Dr. David Alan Gilbert" , Paolo Bonzini Cc: Roman Kagan , "ehabkost@redhat.com" , "kvm@vger.kernel.org" , "mst@redhat.com" , "quintela@redhat.com" , "linux-kernel@vger.kernel.org" , "qemu-devel@nongnu.org" , "linux-mm@kvack.org" , "amit.shah@redhat.com" , "akpm@linux-foundation.org" , "virtualization@lists.linux-foundation.org" , "rth@twiddle.net" > > On 04/03/2016 15:26, Li, Liang Z wrote: > > >> > > > >> > The memory usage will keep increasing due to ever growing caches, > > >> > etc, so you'll be left with very little free memory fairly soon. > > >> > > > > I don't think so. > > > > > > > Roman is right. For example, here I am looking at a 64 GB (physical) > > machine which was booted about 30 minutes ago, and which is running > > disk-heavy workloads (installing VMs). > > > > Since I have started writing this email (2 minutes?), the amount of > > free memory has already gone down from 37 GB to 33 GB. I expect that > > by the time I have finished running the workload, in two hours, it > > will not have any free memory. >=20 > But what about a VM sitting idle, or that just has more RAM assigned to i= t > than is currently using. > I've got a host here that's been up for 46 days and has been doing some > heavy VM debugging a few days ago, but today: >=20 > # free -m > total used free shared buff/cache ava= ilable > Mem: 96536 1146 44834 184 50555 = 94735 >=20 > I very rarely use all it's RAM, so it's got a big chunk of free RAM, and = yes it's > got a big chunk of cache as well. >=20 > Dave >=20 > > > > Paolo I begin to realize Roman's opinions. The PV solution can't handle the cache= memory while inflating balloon could. Inflating balloon so as to skipping the cache memory is no good for guest's= performance. How much of the free memory in the guest depends on the workload in the VM = and the time VM has already run before live migration. Even the memory usage will keep increasing due to ev= er growing caches, but we don't know when the live migration will happen, assuming there are no or very little f= ree pages in the guest is not quite right. The advantage of the pv solution is the smaller performance impact, compari= ng with inflating the balloon. Liang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org