> 2020年7月16日 14:39，Michael S. Tsirkin <mst@xxxxxxxxxx> 写道：
>
> On Thu, Jul 16, 2020 at 10:41:55AM +0800, Hui Zhu wrote:
>> This commit adds a vq dcvq to deflate continuous pages.
>> When VIRTIO_BALLOON_F_CONT_PAGES is set, try to get continuous pages
>> from icvq and use madvise MADV_WILLNEED with the pages.
>>
>> Signed-off-by: Hui Zhu <teawaterz@xxxxxxxxxxxxxxxxx>
>
> This is arguably something to benchmark. Does guest benefit
> from MADV_WILLNEED or loose performance?
MADV_WILLNEED will call madvise_willneed in the host kernel.
madvise_willneed will schedule all required I/O operations (swap in or vfs_fadvise POSIX_FADV_WILLNEED) of the address.
But the pages of the balloon are released by MADV_DONTNEED.
So I think MADV_WILLNEED will not affect the performance of the guest in the most of situations.
Best,
Hui
>
>> ---
>> hw/virtio/virtio-balloon.c | 14 +++++++++-----
>> include/hw/virtio/virtio-balloon.h | 2 +-
>> 2 files changed, 10 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
>> index d36a5c8..165adf7 100644
>> --- a/hw/virtio/virtio-balloon.c
>> +++ b/hw/virtio/virtio-balloon.c
>> @@ -138,7 +138,8 @@ static void balloon_inflate_page(VirtIOBalloon *balloon,
>> }
>>
>> static void balloon_deflate_page(VirtIOBalloon *balloon,
>> - MemoryRegion *mr, hwaddr mr_offset)
>> + MemoryRegion *mr, hwaddr mr_offset,
>> + size_t size)
>> {
>> void *addr = memory_region_get_ram_ptr(mr) + mr_offset;
>> ram_addr_t rb_offset;
>> @@ -153,10 +154,11 @@ static void balloon_deflate_page(VirtIOBalloon *balloon,
>> rb_page_size = qemu_ram_pagesize(rb);
>>
>> host_addr = (void *)((uintptr_t)addr & ~(rb_page_size - 1));
>> + size &= ~(rb_page_size - 1);
>>
>> /* When a page is deflated, we hint the whole host page it lives
>> * on, since we can't do anything smaller */
>> - ret = qemu_madvise(host_addr, rb_page_size, QEMU_MADV_WILLNEED);
>> + ret = qemu_madvise(host_addr, size, QEMU_MADV_WILLNEED);
>> if (ret != 0) {
>> warn_report("Couldn't MADV_WILLNEED on balloon deflate: %s",
>> strerror(errno));
>> @@ -354,7 +356,7 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>> pa = (hwaddr) p << VIRTIO_BALLOON_PFN_SHIFT;
>> offset += 4;
>>
>> - if (vq == s->icvq) {
>> + if (vq == s->icvq || vq == s->dcvq) {
>> uint32_t psize_ptr;
>> if (iov_to_buf(elem->out_sg, elem->out_num, offset, &psize_ptr, 4) != 4) {
>> break;
>> @@ -383,8 +385,9 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>> balloon_inflate_page(s, section.mr,
>> section.offset_within_region,
>> psize, &pbp);
>> - } else if (vq == s->dvq) {
>> - balloon_deflate_page(s, section.mr, section.offset_within_region);
>> + } else if (vq == s->dvq || vq == s->dcvq) {
>> + balloon_deflate_page(s, section.mr, section.offset_within_region,
>> + psize);
>> } else {
>> g_assert_not_reached();
>> }
>> @@ -838,6 +841,7 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>>
>> if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_CONT_PAGES)) {
>> s->icvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>> + s->dcvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>> }
>>
>> reset_stats(s);
>> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
>> index 6a2514d..848a7fb 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, *icvq;
>> + VirtQueue *ivq, *dvq, *svq, *free_page_vq, *icvq, *dcvq;
>> uint32_t free_page_report_status;
>> uint32_t num_pages;
>> uint32_t actual;
>> --
>> 2.7.4
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: virtio-dev-unsubscribe@xxxxxxxxxxxxxxxxxxxx
> For additional commands, e-mail: virtio-dev-help@xxxxxxxxxxxxxxxxxxxx
