From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753423Ab2ICGfc (ORCPT ); Mon, 3 Sep 2012 02:35:32 -0400 Received: from mail-wi0-f178.google.com ([209.85.212.178]:34240 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751136Ab2ICGfa (ORCPT ); Mon, 3 Sep 2012 02:35:30 -0400 Message-ID: <50444FAF.7030304@redhat.com> Date: Mon, 03 Sep 2012 08:35:27 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Rusty Russell CC: Frank Swiderski , "Michael S. Tsirkin" , Andrea Arcangeli , Rik van Riel , Rafael Aquini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mikew@google.com, Ying Han , virtualization@lists.linux-foundation.org Subject: Re: [PATCH] Add a page cache-backed balloon device driver. References: <1340742778-11282-1-git-send-email-fes@google.com> <4FEA1E2E.4020806@redhat.com> <20120626214709.GA15406@redhat.com> <87obnzxaxv.fsf@rustcorp.com.au> In-Reply-To: <87obnzxaxv.fsf@rustcorp.com.au> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 02/07/2012 02:29, Rusty Russell ha scritto: > VIRTIO_BALLOON_F_MUST_TELL_HOST > implies you should tell the host (eventually). I don't know if any > implementations actually care though. This is indeed broken, because it is a "negative" feature: it tells you that "implicit deflate" is _not_ supported. Right now, QEMU refuses migration if the target does not support all the features that were negotiated. But then: - a migration from non-MUST_TELL_HOST to MUST_TELL_HOST will succeed, which is wrong; - a migration from MUST_TELL_HOST to non-MUST_TELL_HOST will fail, which is useless. > We could add a VIRTIO_BALLOON_F_NEVER_TELL_DEFLATE which would mean the > deflate vq need not be used at all. That would work. At the same time we could deprecate MUST_TELL_HOST. Certainly the guest implementations don't care, or we would have experienced problems such as the one above. The QEMU implementation also does not care but, for example, a Xen implementation would care. Paolo From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] Add a page cache-backed balloon device driver. Date: Mon, 03 Sep 2012 08:35:27 +0200 Message-ID: <50444FAF.7030304@redhat.com> References: <1340742778-11282-1-git-send-email-fes@google.com> <4FEA1E2E.4020806@redhat.com> <20120626214709.GA15406@redhat.com> <87obnzxaxv.fsf@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Frank Swiderski , Andrea Arcangeli , Rik van Riel , Rafael Aquini , kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, mikew@google.com, Ying Han , virtualization@lists.linux-foundation.org To: Rusty Russell Return-path: In-Reply-To: <87obnzxaxv.fsf@rustcorp.com.au> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: kvm.vger.kernel.org Il 02/07/2012 02:29, Rusty Russell ha scritto: > VIRTIO_BALLOON_F_MUST_TELL_HOST > implies you should tell the host (eventually). I don't know if any > implementations actually care though. This is indeed broken, because it is a "negative" feature: it tells you that "implicit deflate" is _not_ supported. Right now, QEMU refuses migration if the target does not support all the features that were negotiated. But then: - a migration from non-MUST_TELL_HOST to MUST_TELL_HOST will succeed, which is wrong; - a migration from MUST_TELL_HOST to non-MUST_TELL_HOST will fail, which is useless. > We could add a VIRTIO_BALLOON_F_NEVER_TELL_DEFLATE which would mean the > deflate vq need not be used at all. That would work. At the same time we could deprecate MUST_TELL_HOST. Certainly the guest implementations don't care, or we would have experienced problems such as the one above. The QEMU implementation also does not care but, for example, a Xen implementation would care. Paolo