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Date: Thu, 26 Mar 2020 03:07:45 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: teawater <teawaterz@...ux.alibaba.com>
Cc: Hui Zhu <teawater@...il.com>, jasowang@...hat.com,
akpm@...ux-foundation.org, pagupta@...hat.com,
mojha@...eaurora.org, david@...hat.com, namit@...are.com,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, qemu-devel@...gnu.org
Subject: Re: [RFC for QEMU] virtio-balloon: Add option thp-order to set
VIRTIO_BALLOON_F_THP_ORDER
On Tue, Mar 17, 2020 at 06:13:32PM +0800, teawater wrote:
>
>
> > 2020年3月12日 16:25，Michael S. Tsirkin <mst@...hat.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@...ux.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
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