From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755614AbbFQRcY (ORCPT ); Wed, 17 Jun 2015 13:32:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15541 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753338AbbFQRcQ (ORCPT ); Wed, 17 Jun 2015 13:32:16 -0400 Date: Wed, 17 Jun 2015 19:32:10 +0200 From: Igor Mammedov To: Paolo Bonzini Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions Message-ID: <20150617193210.390228a4@igors-macbook-pro.local> In-Reply-To: <5581A496.5060503@redhat.com> References: <20150617151030-mutt-send-email-mst@redhat.com> <5581742C.9060100@redhat.com> <20150617163028-mutt-send-email-mst@redhat.com> <20150617171257.11fe405d@nial.brq.redhat.com> <20150617173736-mutt-send-email-mst@redhat.com> <20150617180921.7972345d@igors-macbook-pro.local> <20150617182917-mutt-send-email-mst@redhat.com> <5581A0E4.6050100@redhat.com> <20150617183413-mutt-send-email-mst@redhat.com> <5581A281.4000308@redhat.com> <20150617183936-mutt-send-email-mst@redhat.com> <5581A496.5060503@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 17 Jun 2015 18:47:18 +0200 Paolo Bonzini wrote: > > > On 17/06/2015 18:41, Michael S. Tsirkin wrote: > > On Wed, Jun 17, 2015 at 06:38:25PM +0200, Paolo Bonzini wrote: > >> > >> > >> On 17/06/2015 18:34, Michael S. Tsirkin wrote: > >>> On Wed, Jun 17, 2015 at 06:31:32PM +0200, Paolo Bonzini wrote: > >>>> > >>>> > >>>> On 17/06/2015 18:30, Michael S. Tsirkin wrote: > >>>>> Meanwhile old tools are vulnerable to OOM attacks. > >>>> > >>>> For each vhost device there will be likely one tap interface, > >>>> and I suspect that it takes way, way more than 16KB of memory. > >>> > >>> That's not true. We have a vhost device per queue, all queues > >>> are part of a single tap device. > >> > >> s/tap/VCPU/ then. A KVM VCPU also takes more than 16KB of memory. > > > > That's up to you as a kvm maintainer :) > > Not easy, when the CPU alone requires three (albeit non-consecutive) > pages for the VMCS, the APIC access page and the EPT root. > > > People are already concerned about vhost device > > memory usage, I'm not happy to define our user/kernel interface > > in a way that forces even more memory to be used up. > > So, the questions to ask are: > > 1) What is the memory usage like immediately after vhost is brought > up, apart from these 16K? > > 2) Is there anything in vhost that allocates a user-controllable > amount of memory? > > 3) What is the size of the data structures that support one virtqueue > (there are two of them)? Does it depend on the size of the > virtqueues? > > 4) Would it make sense to share memory regions between multiple vhost > devices? Would it be hard to implement? It would also make memory > operations O(1) rather than O(#cpus). > > Paolo in addition to that could vhost share memmap with KVM i.e. use its memslots instead of duplicating it?