linux-kernel - RE: [RFC qemu 2/4] virtio-balloon: Add a new feature to balloon device

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Date:	Fri, 4 Mar 2016 02:38:29 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
CC:	"quintela@...hat.com" <quintela@...hat.com>,
	"amit.shah@...hat.com" <amit.shah@...hat.com>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"rth@...ddle.net" <rth@...ddle.net>,
	"ehabkost@...hat.com" <ehabkost@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"dgilbert@...hat.com" <dgilbert@...hat.com>
Subject: RE: [RFC qemu 2/4] virtio-balloon: Add a new feature to balloon
 device

> On Thu,  3 Mar 2016 18:44:26 +0800
> Liang Li <liang.z.li@...el.com> wrote:
> 
> > Extend the virtio balloon device to support a new feature, this new
> > feature can help to get guest's free pages information, which can be
> > used for live migration optimzation.
> 
> Do you have a spec for this, e.g. as a patch to the virtio spec?

Not yet.
> 
> >
> > Signed-off-by: Liang Li <liang.z.li@...el.com>
> > ---
> >  balloon.c                                       | 30 ++++++++-
> >  hw/virtio/virtio-balloon.c                      | 81 ++++++++++++++++++++++++-
> >  include/hw/virtio/virtio-balloon.h              | 17 +++++-
> >  include/standard-headers/linux/virtio_balloon.h |  1 +
> >  include/sysemu/balloon.h                        | 10 ++-
> >  5 files changed, 134 insertions(+), 5 deletions(-)
> 
> > +static int virtio_balloon_free_pages(void *opaque,
> > +                                     unsigned long *free_pages_bitmap,
> > +                                     unsigned long *free_pages_count)
> > +{
> > +    VirtIOBalloon *s = opaque;
> > +    VirtIODevice *vdev = VIRTIO_DEVICE(s);
> > +    VirtQueueElement *elem = s->free_pages_vq_elem;
> > +    int len;
> > +
> > +    if (!balloon_free_pages_supported(s)) {
> > +        return -1;
> > +    }
> > +
> > +    if (s->req_status == NOT_STARTED) {
> > +        s->free_pages_bitmap = free_pages_bitmap;
> > +        s->req_status = STARTED;
> > +        s->mem_layout.low_mem =
> > + pc_get_lowmem(PC_MACHINE(current_machine));
> 
> Please don't leak pc-specific information into generic code.

I have already notice that and just leave it here in this  initial RFC version,  
the hard part of this solution is how to handle different architecture ...

Thanks!

Liang