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

>
>> ---
>> 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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