2020年7月16日 14:43，Michael S. Tsirkin [off-list ref] 写道：

On Thu, Jul 16, 2020 at 10:41:51AM +0800, Hui Zhu wrote:

quoted

diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index dc3e656..4d0151a 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h

@@ -37,6 +37,7 @@

#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_REPORTING	5 /* Page reporting virtqueue */
+#define VIRTIO_BALLOON_F_CONT_PAGES	6 /* VQ to report continuous pages */

/* Size of a PFN in the balloon interface. */
#define VIRTIO_BALLOON_PFN_SHIFT 12

So how does the guest/host interface look like?
Could you write up something about it?

Continuous pages are report by num_pfns and pfns in virtio_balloon too.
The function to set pfns is set_page_pfns_size in https://github.com/teawater/linux/blob/balloon_conts/drivers/virtio/virtio_balloon.c#L221

static void set_page_pfns_size(struct virtio_balloon *vb,
                               __virtio32 pfns[], struct page *page,
                               size_t size)
{
        /* Set the first pfn of the continuous pages.  */
        pfns[0] = cpu_to_virtio32(vb->vdev, page_to_balloon_pfn(page));
        /* Set the size of the continuous pages.  */
        pfns[1] = (__virtio32) size;
}

Each of continuous pages need 2 pfn.
The first pfn of the pages is set to pfns[0].  The size of the pages is set to pfns[1].

The pfn is 32 bits.
So the max order of inflate continuous pages is VIRTIO_BALLOON_INFLATE_MAX_ORDER.
#define VIRTIO_BALLOON_INFLATE_MAX_ORDER min((int) (sizeof(__virtio32) * BITS_PER_BYTE - \
                                                    1 - PAGE_SHIFT), (MAX_ORDER-1))

The max page number of deflate continuous pages is VIRTIO_BALLOON_DEFLATE_MAX_PAGES_NUM.
#define VIRTIO_BALLOON_DEFLATE_MAX_PAGES_NUM (((__virtio32)~0U) >> PAGE_SHIFT)

Best,
Hui