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Date: Thu, 12 Mar 2020 04:25:07 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Hui Zhu <teawater@...il.com>
Cc: 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,
Hui Zhu <teawaterz@...ux.alibaba.com>
Subject: Re: [RFC for QEMU] virtio-balloon: Add option thp-order to set
VIRTIO_BALLOON_F_THP_ORDER
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.
> ---
> 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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