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SubjectRe: [PATCH v3 QEMU 2/2] virtio-balloon: Provide a interface for unused page reporting
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On Fri, 2019-08-02 at 16:40 -0400, Nitesh Narayan Lal wrote:
> On 8/1/19 6:43 PM, Alexander Duyck wrote:
> > From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> >
> > Add support for what I am referring to as "unused page reporting".
> > Basically the idea is to function very similar to how the balloon works
> > in that we basically end up madvising the page as not being used. However
> > we don't really need to bother with any deflate type logic since the page
> > will be faulted back into the guest when it is read or written to.
> >
> > This is meant to be a simplification of the existing balloon interface
> > to use for providing hints to what memory needs to be freed. I am assuming
> > this is safe to do as the deflate logic does not actually appear to do very
> > much other than tracking what subpages have been released and which ones
> > haven't.
> >
> > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> > ---
> > hw/virtio/virtio-balloon.c | 46 ++++++++++++++++++++++-
> > include/hw/virtio/virtio-balloon.h | 2 +
> > include/standard-headers/linux/virtio_balloon.h | 1 +
> > 3 files changed, 46 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> > index 003b3ebcfdfb..7a30df63bc77 100644
> > --- a/hw/virtio/virtio-balloon.c
> > +++ b/hw/virtio/virtio-balloon.c
> > @@ -320,6 +320,40 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
> > balloon_stats_change_timer(s, 0);
> > }
> >
> > +static void virtio_balloon_handle_report(VirtIODevice *vdev, VirtQueue *vq)
> > +{
> > + VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> > + VirtQueueElement *elem;
> > +
> > + while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
> > + unsigned int i;
> > +
> > + for (i = 0; i < elem->in_num; i++) {
> > + void *addr = elem->in_sg[i].iov_base;
> > + size_t size = elem->in_sg[i].iov_len;
> > + ram_addr_t ram_offset;
> > + size_t rb_page_size;
> > + RAMBlock *rb;
> > +
> > + if (qemu_balloon_is_inhibited() || dev->poison_val)
> > + continue;
> > +
> > + rb = qemu_ram_block_from_host(addr, false, &ram_offset);
> > + rb_page_size = qemu_ram_pagesize(rb);
> > +
> > + /* For now we will simply ignore unaligned memory regions */
> > + if ((ram_offset | size) & (rb_page_size - 1))
> > + continue;
> > +
> > + ram_block_discard_range(rb, ram_offset, size);
> > + }
> > +
> > + virtqueue_push(vq, elem, 0);
> > + virtio_notify(vdev, vq);
> > + g_free(elem);
> > + }
> > +}
> > +
> > static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
> > {
> > VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
> > @@ -627,7 +661,8 @@ static size_t virtio_balloon_config_size(VirtIOBalloon *s)
> > return sizeof(struct virtio_balloon_config);
> > }
> > if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON) ||
> > - virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> > + virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT) ||
> > + virtio_has_feature(features, VIRTIO_BALLOON_F_REPORTING)) {
> > return sizeof(struct virtio_balloon_config);
> > }
> > return offsetof(struct virtio_balloon_config, free_page_report_cmd_id);
> > @@ -715,7 +750,8 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
> > VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> > f |= dev->host_features;
> > virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
> > - if (virtio_has_feature(f, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> > + if (virtio_has_feature(f, VIRTIO_BALLOON_F_FREE_PAGE_HINT) ||
> > + virtio_has_feature(f, VIRTIO_BALLOON_F_REPORTING)) {
> > virtio_add_feature(&f, VIRTIO_BALLOON_F_PAGE_POISON);
> > }
> >
> > @@ -805,6 +841,10 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
> > s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
> > s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
> >
> > + if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_REPORTING)) {
> > + s->rvq = virtio_add_queue(vdev, 32, virtio_balloon_handle_report);
> > + }
> > +
> This does makes sense. I haven't seen the kernel patch yet, but I am guessing
> you will use this max_vq size to define the capacity.

Right. It was one of the suggestions I had received for the last patch
set. So since I was already using it to limit the capacity I thought I
might as well shrink the size of the queue on the hypervisor and save
space.

> > if (virtio_has_feature(s->host_features,
> > VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> > s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
> > @@ -931,6 +971,8 @@ static Property virtio_balloon_properties[] = {
> > */
> > DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,
> > qemu_4_0_config_size, false),
> > + DEFINE_PROP_BIT("unused-page-reporting", VirtIOBalloon, host_features,
> > + VIRTIO_BALLOON_F_REPORTING, true),
> > DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,
> > IOThread *),
> > DEFINE_PROP_END_OF_LIST(),
> > diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
> > index 7fe78e5c14d7..db5bf7127112 100644
> > --- a/include/hw/virtio/virtio-balloon.h
> > +++ b/include/hw/virtio/virtio-balloon.h
> > @@ -42,7 +42,7 @@ enum virtio_balloon_free_page_report_status {
> >
> > typedef struct VirtIOBalloon {
> > VirtIODevice parent_obj;
> > - VirtQueue *ivq, *dvq, *svq, *free_page_vq;
> > + VirtQueue *ivq, *dvq, *svq, *free_page_vq, *rvq;
> > uint32_t free_page_report_status;
> > uint32_t num_pages;
> > uint32_t actual;
> > diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
> > index 9375ca2a70de..1c5f6d6f2de6 100644
> > --- a/include/standard-headers/linux/virtio_balloon.h
> > +++ b/include/standard-headers/linux/virtio_balloon.h
> > @@ -36,6 +36,7 @@
> > #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
> > #define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */
> > #define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */
> > +#define VIRTIO_BALLOON_F_REPORTING 5 /* Page reporting virtqueue */
>
> Do we really need this change? or is this something which is picked from the
> Linux kernel?
> If we do need it, then Cornelia suggested to split off any update to this header
> into a separate patch, so that it can be replaced by a proper headers update
> when it is merged.

I'll keep that in mind. I didn't think of this as an official submission
for QEMU as of yet. I have been mostly focused on the kernel side of
things for now.


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