[Qemu-devel] [PATCH v2 repost 7/7] virtio-balloon: tell host vm's free page info

[Liang Li]

Support the request for vm's free page information, response with
a page bitmap. QEMU can make use of this free page bitmap to speed
up live migration process by skipping process the free pages.

Signed-off-by: Liang Li <address@hidden>
Cc: Michael S. Tsirkin <address@hidden>
Cc: Andrew Morton <address@hidden>
Cc: Vlastimil Babka <address@hidden>
Cc: Mel Gorman <address@hidden>
Cc: Paolo Bonzini <address@hidden>
Cc: Cornelia Huck <address@hidden>
Cc: Amit Shah <address@hidden>
---
 drivers/virtio/virtio_balloon.c | 104 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 98 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 2d18ff6..5ca4ad3 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -62,10 +62,13 @@ module_param(oom_pages, int, S_IRUSR | S_IWUSR);
 MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
 
 extern unsigned long get_max_pfn(void);
+extern int get_free_pages(unsigned long start_pfn, unsigned long end_pfn,
+               unsigned long *bitmap, unsigned long len);
+
 
 struct virtio_balloon {
        struct virtio_device *vdev;
-       struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
+       struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *misc_vq;
 
        /* The balloon servicing is delegated to a freezable workqueue. */
        struct work_struct update_balloon_stats_work;
@@ -89,6 +92,8 @@ struct virtio_balloon {
        unsigned long pfn_limit;
        /* Used to record the processed pfn range */
        unsigned long min_pfn, max_pfn, start_pfn, end_pfn;
+       /* Request header */
+       struct balloon_req_hdr req_hdr;
        /*
         * The pages we've told the Host we're not using are enqueued
         * at vb_dev_info->pages list.
@@ -373,6 +378,49 @@ static void update_balloon_stats(struct virtio_balloon *vb)
                                pages_to_bytes(available));
 }
 
+static void update_free_pages_stats(struct virtio_balloon *vb,
+                               unsigned long req_id)
+{
+       struct scatterlist sg_in, sg_out;
+       unsigned long pfn = 0, bmap_len, max_pfn;
+       struct virtqueue *vq = vb->misc_vq;
+       struct balloon_bmap_hdr *hdr = vb->bmap_hdr;
+       int ret = 1;
+
+       max_pfn = get_max_pfn();
+       mutex_lock(&vb->balloon_lock);
+       while (pfn < max_pfn) {
+               memset(vb->page_bitmap, 0, vb->bmap_len);
+               ret = get_free_pages(pfn, pfn + vb->pfn_limit,
+                       vb->page_bitmap, vb->bmap_len * BITS_PER_BYTE);
+               hdr->cmd = cpu_to_virtio16(vb->vdev, BALLOON_GET_FREE_PAGES);
+               hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
+               hdr->req_id = cpu_to_virtio64(vb->vdev, req_id);
+               hdr->start_pfn = cpu_to_virtio64(vb->vdev, pfn);
+               bmap_len = vb->pfn_limit / BITS_PER_BYTE;
+               if (!ret) {
+                       hdr->flag = cpu_to_virtio16(vb->vdev,
+                                                       BALLOON_FLAG_DONE);
+                       if (pfn + vb->pfn_limit > max_pfn)
+                               bmap_len = (max_pfn - pfn) / BITS_PER_BYTE;
+               } else
+                       hdr->flag = cpu_to_virtio16(vb->vdev,
+                                                       BALLOON_FLAG_CONT);
+               hdr->bmap_len = cpu_to_virtio64(vb->vdev, bmap_len);
+               sg_init_one(&sg_out, hdr,
+                        sizeof(struct balloon_bmap_hdr) + bmap_len);
+
+               virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL);
+               virtqueue_kick(vq);
+               pfn += vb->pfn_limit;
+       }
+
+       sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
+       virtqueue_add_inbuf(vq, &sg_in, 1, &vb->req_hdr, GFP_KERNEL);
+       virtqueue_kick(vq);
+       mutex_unlock(&vb->balloon_lock);
+}
+
 /*
  * While most virtqueues communicate guest-initiated requests to the 
hypervisor,
  * the stats queue operates in reverse.  The driver initializes the virtqueue
@@ -511,18 +559,49 @@ static void update_balloon_size_func(struct work_struct 
*work)
                queue_work(system_freezable_wq, work);
 }
 
+static void misc_handle_rq(struct virtio_balloon *vb)
+{
+       struct balloon_req_hdr *ptr_hdr;
+       unsigned int len;
+
+       ptr_hdr = virtqueue_get_buf(vb->misc_vq, &len);
+       if (!ptr_hdr || len != sizeof(vb->req_hdr))
+               return;
+
+       switch (ptr_hdr->cmd) {
+       case BALLOON_GET_FREE_PAGES:
+               update_free_pages_stats(vb, ptr_hdr->param);
+               break;
+       default:
+               break;
+       }
+}
+
+static void misc_request(struct virtqueue *vq)
+{
+       struct virtio_balloon *vb = vq->vdev->priv;
+
+       misc_handle_rq(vb);
+}
+
 static int init_vqs(struct virtio_balloon *vb)
 {
-       struct virtqueue *vqs[3];
-       vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request 
};
-       static const char * const names[] = { "inflate", "deflate", "stats" };
+       struct virtqueue *vqs[4];
+       vq_callback_t *callbacks[] = { balloon_ack, balloon_ack,
+                                        stats_request, misc_request };
+       static const char * const names[] = { "inflate", "deflate", "stats",
+                                                "misc" };
        int err, nvqs;
 
        /*
         * We expect two virtqueues: inflate and deflate, and
         * optionally stat.
         */
-       nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ))
+               nvqs = 4;
+       else
+               nvqs = virtio_has_feature(vb->vdev,
+                                         VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
        err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
        if (err)
                return err;
@@ -543,6 +622,16 @@ static int init_vqs(struct virtio_balloon *vb)
                        BUG();
                virtqueue_kick(vb->stats_vq);
        }
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ)) {
+               struct scatterlist sg_in;
+
+               vb->misc_vq = vqs[3];
+               sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
+               if (virtqueue_add_inbuf(vb->misc_vq, &sg_in, 1,
+                   &vb->req_hdr, GFP_KERNEL) < 0)
+                       BUG();
+               virtqueue_kick(vb->misc_vq);
+       }
        return 0;
 }
 
@@ -639,8 +728,10 @@ static int virtballoon_probe(struct virtio_device *vdev)
        vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
 
        /* Clear the feature bit if memory allocation fails */
-       if (!vb->bmap_hdr)
+       if (!vb->bmap_hdr) {
                __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
+               __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_MISC_VQ);
+       }
        else
                vb->page_bitmap = vb->bmap_hdr + hdr_len;
        mutex_init(&vb->balloon_lock);
@@ -743,6 +834,7 @@ static unsigned int features[] = {
        VIRTIO_BALLOON_F_STATS_VQ,
        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
        VIRTIO_BALLOON_F_PAGE_BITMAP,
+       VIRTIO_BALLOON_F_MISC_VQ,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
-- 
1.9.1