VIRTIO_BALLOON_PFN_SHIFT   28 drivers/virtio/virtio_balloon.c #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
VIRTIO_BALLOON_PFN_SHIFT  127 drivers/virtio/virtio_balloon.c 	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);