From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757407Ab2F0QIl (ORCPT ); Wed, 27 Jun 2012 12:08:41 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:37516 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753831Ab2F0QIj convert rfc822-to-8bit (ORCPT ); Wed, 27 Jun 2012 12:08:39 -0400 MIME-Version: 1.0 In-Reply-To: <20120627160644.GD21393@redhat.com> References: <1340742778-11282-1-git-send-email-fes@google.com> <20120626214106.GC14054@redhat.com> <87lij91myw.fsf@rustcorp.com.au> <20120627160644.GD21393@redhat.com> Date: Wed, 27 Jun 2012 09:08:37 -0700 Message-ID: Subject: Re: [PATCH] Add a page cache-backed balloon device driver. From: Frank Swiderski To: "Michael S. Tsirkin" Cc: Rusty Russell , riel@redhat.com, Andrea Arcangeli , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, mikew@google.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 27, 2012 at 9:06 AM, Michael S. Tsirkin wrote: > On Wed, Jun 27, 2012 at 08:48:55AM -0700, Frank Swiderski wrote: >> On Tue, Jun 26, 2012 at 7:56 PM, Rusty Russell wrote: >> > On Wed, 27 Jun 2012 00:41:06 +0300, "Michael S. Tsirkin" wrote: >> >> On Tue, Jun 26, 2012 at 01:32:58PM -0700, Frank Swiderski wrote: >> >> > This implementation of a virtio balloon driver uses the page cache to >> >> > "store" pages that have been released to the host.  The communication >> >> > (outside of target counts) is one way--the guest notifies the host when >> >> > it adds a page to the page cache, allowing the host to madvise(2) with >> >> > MADV_DONTNEED.  Reclaim in the guest is therefore automatic and implicit >> >> > (via the regular page reclaim).  This means that inflating the balloon >> >> > is similar to the existing balloon mechanism, but the deflate is >> >> > different--it re-uses existing Linux kernel functionality to >> >> > automatically reclaim. >> >> > >> >> > Signed-off-by: Frank Swiderski >> >> >> >> I'm pondering this: >> >> >> >> Should it really be a separate driver/device ID? >> >> If it behaves the same from host POV, maybe it >> >> should be up to the guest how to inflate/deflate >> >> the balloon internally? >> > >> > Well, it shouldn't steal ID 10, either way :)  Either use a completely >> > bogus number, or ask for an id. >> > >> > But AFAICT this should be a an alternate driver of for the same device: >> > it's not really a separate device, is it? >> > >> > Cheers, >> > Rusty. >> >> Apologies, Rusty.  Asking for an ID is in the virtio spec, and I >> completely neglected that step.  Though as you and others have pointed >> out, this probably fits better as a different driver for the same >> device.  Since it changes whether or not the deflate operation is >> necessary, it also seems that how this should look is different >> behavior based on a feature bit in the device. >> >> If that sounds reasonable, then what I'll do with this patch is merge >> it with the existing virtio balloon driver with a feature bit for >> determining which behavior to use. >> >> I also think the idea of a generic balloon that the different balloon >> drivers use for the inflate/deflate operations is interesting and >> useful, though I think the suggestion of pending that until later is >> correct. >> >> Sounds reasonable? >> >> Regards, >> fes > > I think a spec patch would be a good spec at this point. > You can get the spec from Rusty, or a mirror > from my git: > > git://git.kernel.org/pub/scm/virt/kvm/mst/virtio-spec.git > > > Got it, thanks, will do. Regards, fes