Re: [RFC for QEMU] virtio-balloon: Add option thp-order to set VIRTIO_BALLOON_F_THP_ORDER

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 17, 2020 at 06:13:32PM +0800, teawater wrote:
> 
> 
> > 2020年3月12日 16:25，Michael S. Tsirkin <mst@redhat.com> 写道：
> > 
> > On Thu, Mar 12, 2020 at 03:49:55PM +0800, Hui Zhu wrote:
> >> If the guest kernel has many fragmentation pages, use virtio_balloon
> >> will split THP of QEMU when it calls MADV_DONTNEED madvise to release
> >> the balloon pages.
> >> Set option thp-order to on will open flags VIRTIO_BALLOON_F_THP_ORDER.
> >> It will set balloon size to THP size to handle the THP split issue.
> >> 
> >> Signed-off-by: Hui Zhu <teawaterz@linux.alibaba.com>
> > 
> > What's wrong with just using the PartiallyBalloonedPage machinery
> > instead? That would make it guest transparent.
> 
> In balloon_inflate_page:
>     rb_page_size = qemu_ram_pagesize(rb);
> 
>     if (rb_page_size == BALLOON_PAGE_SIZE) {
>         /* Easy case */
> 
> It seems that PartiallyBalloonedPage is only used when rb_page_size is greater than BALLOON_PAGE_SIZE.
> Do you mean I should modify the working mechanism of balloon_inflate_page function?
> 
> Thanks,
> Hui

Yes, we can tweak it to unconditionally combine pages to
a huge page.


> > 
> >> ---
> >> hw/virtio/virtio-balloon.c                      | 67 ++++++++++++++++---------
> >> include/standard-headers/linux/virtio_balloon.h |  4 ++
> >> 2 files changed, 47 insertions(+), 24 deletions(-)
> >> 
> >> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> >> index a4729f7..cfe86b0 100644
> >> --- a/hw/virtio/virtio-balloon.c
> >> +++ b/hw/virtio/virtio-balloon.c
> >> @@ -340,37 +340,49 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
> >>         while (iov_to_buf(elem->out_sg, elem->out_num, offset, &pfn, 4) == 4) {
> >>             unsigned int p = virtio_ldl_p(vdev, &pfn);
> >>             hwaddr pa;
> >> +            size_t handle_size = BALLOON_PAGE_SIZE;
> >> 
> >>             pa = (hwaddr) p << VIRTIO_BALLOON_PFN_SHIFT;
> >>             offset += 4;
> >> 
> >> -            section = memory_region_find(get_system_memory(), pa,
> >> -                                         BALLOON_PAGE_SIZE);
> >> -            if (!section.mr) {
> >> -                trace_virtio_balloon_bad_addr(pa);
> >> -                continue;
> >> -            }
> >> -            if (!memory_region_is_ram(section.mr) ||
> >> -                memory_region_is_rom(section.mr) ||
> >> -                memory_region_is_romd(section.mr)) {
> >> -                trace_virtio_balloon_bad_addr(pa);
> >> -                memory_region_unref(section.mr);
> >> -                continue;
> >> -            }
> >> +            if (virtio_has_feature(s->host_features,
> >> +                                   VIRTIO_BALLOON_F_THP_ORDER))
> >> +                handle_size = BALLOON_PAGE_SIZE << VIRTIO_BALLOON_THP_ORDER;
> >> +
> >> +            while (handle_size > 0) {
> >> +                section = memory_region_find(get_system_memory(), pa,
> >> +                                             BALLOON_PAGE_SIZE);
> >> +                if (!section.mr) {
> >> +                    trace_virtio_balloon_bad_addr(pa);
> >> +                    continue;
> >> +                }
> >> +                if (!memory_region_is_ram(section.mr) ||
> >> +                    memory_region_is_rom(section.mr) ||
> >> +                    memory_region_is_romd(section.mr)) {
> >> +                    trace_virtio_balloon_bad_addr(pa);
> >> +                    memory_region_unref(section.mr);
> >> +                    continue;
> >> +                }
> >> 
> >> -            trace_virtio_balloon_handle_output(memory_region_name(section.mr),
> >> -                                               pa);
> >> -            if (!qemu_balloon_is_inhibited()) {
> >> -                if (vq == s->ivq) {
> >> -                    balloon_inflate_page(s, section.mr,
> >> -                                         section.offset_within_region, &pbp);
> >> -                } else if (vq == s->dvq) {
> >> -                    balloon_deflate_page(s, section.mr, section.offset_within_region);
> >> -                } else {
> >> -                    g_assert_not_reached();
> >> +                trace_virtio_balloon_handle_output(memory_region_name(section.mr),
> >> +                                                   pa);
> >> +                if (!qemu_balloon_is_inhibited()) {
> >> +                    if (vq == s->ivq) {
> >> +                        balloon_inflate_page(s, section.mr,
> >> +                                             section.offset_within_region,
> >> +                                             &pbp);
> >> +                    } else if (vq == s->dvq) {
> >> +                        balloon_deflate_page(s, section.mr,
> >> +                                             section.offset_within_region);
> >> +                    } else {
> >> +                        g_assert_not_reached();
> >> +                    }
> >>                 }
> >> +                memory_region_unref(section.mr);
> >> +
> >> +                pa += BALLOON_PAGE_SIZE;
> >> +                handle_size -= BALLOON_PAGE_SIZE;
> >>             }
> >> -            memory_region_unref(section.mr);
> >>         }
> >> 
> >>         virtqueue_push(vq, elem, offset);
> >> @@ -693,6 +705,8 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
> >> 
> >>     memcpy(&config, config_data, virtio_balloon_config_size(dev));
> >>     dev->actual = le32_to_cpu(config.actual);
> >> +    if (virtio_has_feature(vdev->host_features, VIRTIO_BALLOON_F_THP_ORDER))
> >> +        dev->actual <<= VIRTIO_BALLOON_THP_ORDER;
> >>     if (dev->actual != oldactual) {
> >>         qapi_event_send_balloon_change(vm_ram_size -
> >>                         ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT));
> >> @@ -728,6 +742,9 @@ static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
> >>     }
> >>     if (target) {
> >>         dev->num_pages = (vm_ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
> >> +        if (virtio_has_feature(dev->host_features,
> >> +                               VIRTIO_BALLOON_F_THP_ORDER))
> >> +            dev->num_pages >>= VIRTIO_BALLOON_THP_ORDER;
> >>         virtio_notify_config(vdev);
> >>     }
> >>     trace_virtio_balloon_to_target(target, dev->num_pages);
> >> @@ -916,6 +933,8 @@ static Property virtio_balloon_properties[] = {
> >>                     VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
> >>     DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,
> >>                     VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
> >> +    DEFINE_PROP_BIT("thp-order", VirtIOBalloon, host_features,
> >> +                    VIRTIO_BALLOON_F_THP_ORDER, false),
> >>     /* QEMU 4.0 accidentally changed the config size even when free-page-hint
> >>      * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
> >>      * property retains this quirk for QEMU 4.1 machine types.
> >> diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
> >> index 9375ca2..f54d613 100644
> >> --- a/include/standard-headers/linux/virtio_balloon.h
> >> +++ b/include/standard-headers/linux/virtio_balloon.h
> >> @@ -36,10 +36,14 @@
> >> #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_THP_ORDER	5 /* Set balloon page order to thp order */
> >> 
> >> /* Size of a PFN in the balloon interface. */
> >> #define VIRTIO_BALLOON_PFN_SHIFT 12
> >> 
> >> +/* The order of the balloon page */
> >> +#define VIRTIO_BALLOON_THP_ORDER 9
> >> +
> >> #define VIRTIO_BALLOON_CMD_ID_STOP	0
> >> #define VIRTIO_BALLOON_CMD_ID_DONE	1
> >> struct virtio_balloon_config {
> >> -- 
> >> 2.7.4