Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757937Ab2F0PtC (ORCPT ); Wed, 27 Jun 2012 11:49:02 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:65013 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752113Ab2F0Ps7 convert rfc822-to-8bit (ORCPT ); Wed, 27 Jun 2012 11:48:59 -0400 MIME-Version: 1.0 In-Reply-To: <87lij91myw.fsf@rustcorp.com.au> References: <1340742778-11282-1-git-send-email-fes@google.com> <20120626214106.GC14054@redhat.com> <87lij91myw.fsf@rustcorp.com.au> Date: Wed, 27 Jun 2012 08:48:55 -0700 Message-ID: Subject: Re: [PATCH] Add a page cache-backed balloon device driver. From: Frank Swiderski To: Rusty Russell Cc: "Michael S. Tsirkin" , 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 Content-Length: 2414 Lines: 56 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/