From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753140AbdG1XBt (ORCPT ); Fri, 28 Jul 2017 19:01:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36140 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752805AbdG1XBs (ORCPT ); Fri, 28 Jul 2017 19:01:48 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 7C50BF2942 Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=mst@redhat.com Date: Sat, 29 Jul 2017 02:01:35 +0300 From: "Michael S. Tsirkin" To: Wei Wang Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, mhocko@kernel.org, willy@infradead.org, virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com Subject: Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG Message-ID: <20170729020006-mutt-send-email-mst@kernel.org> References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-6-git-send-email-wei.w.wang@intel.com> <597AF4EF.4020705@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <597AF4EF.4020705@intel.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 28 Jul 2017 23:01:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 28, 2017 at 04:25:19PM +0800, Wei Wang wrote: > On 07/12/2017 08:40 PM, Wei Wang wrote: > > Add a new feature, VIRTIO_BALLOON_F_SG, which enables to > > transfer a chunk of ballooned (i.e. inflated/deflated) pages using > > scatter-gather lists to the host. > > > > The implementation of the previous virtio-balloon is not very > > efficient, because the balloon pages are transferred to the > > host one by one. Here is the breakdown of the time in percentage > > spent on each step of the balloon inflating process (inflating > > 7GB of an 8GB idle guest). > > > > 1) allocating pages (6.5%) > > 2) sending PFNs to host (68.3%) > > 3) address translation (6.1%) > > 4) madvise (19%) > > > > It takes about 4126ms for the inflating process to complete. > > The above profiling shows that the bottlenecks are stage 2) > > and stage 4). > > > > This patch optimizes step 2) by transferring pages to the host in > > sgs. An sg describes a chunk of guest physically continuous pages. > > With this mechanism, step 4) can also be optimized by doing address > > translation and madvise() in chunks rather than page by page. > > > > With this new feature, the above ballooning process takes ~491ms > > resulting in an improvement of ~88%. > > > > > I found a recent mm patch, bb01b64cfab7c22f3848cb73dc0c2b46b8d38499 > , zeros all the ballooned pages, which is very time consuming. > > Tests show that the time to balloon 7G pages is increased from ~491 ms to > 2.8 seconds with the above patch. Sounds like it should be reverted. Post a revert pls and we'll discuss. > How about moving the zero operation to the hypervisor? In this way, we > will have a much faster balloon process. > > > Best, > Wei Or in other words hypervisors should not be stupid and should not try to run ksm on DONTNEED pages. -- MST