On Fri, Mar 03, 2017 at 01:40:28PM +0800, Wei Wang wrote:
> From: Liang Li <liang.z.li@xxxxxxxxx>
>
> The implementation of the current virtio-balloon is not very
> efficient, because the pages are transferred to the host one by one.
> Here is the breakdown of the time in percentage spent on each
> step of the balloon inflating process (inflating 7GB of an 8GB
> idle guest).
>
> 1) allocating pages (6.5%)
> 2) sending PFNs to host (68.3%)
> 3) address translation (6.1%)
> 4) madvise (19%)
>
> It takes about 4126ms for the inflating process to complete.
> The above profiling shows that the bottlenecks are stage 2)
> and stage 4).
>
> This patch optimizes step 2) by transfering pages to the host in
> chunks. A chunk consists of guest physically continuous pages, and
> it is offered to the host via a base PFN (i.e. the start PFN of
> those physically continuous pages) and the size (i.e. the total
> number of the pages). A normal chunk is formated as below:
> -----------------------------------------------
> | Base (52 bit) | Size (12 bit)|
> -----------------------------------------------
> For large size chunks, an extended chunk format is used:
> -----------------------------------------------
> | Base (64 bit) |
> -----------------------------------------------
> -----------------------------------------------
> | Size (64 bit) |
> -----------------------------------------------
>
> By doing so, step 4) can also be optimized by doing address
> translation and madvise() in chunks rather than page by page.
>
> This optimization requires the negotation of a new feature bit,
> VIRTIO_BALLOON_F_CHUNK_TRANSFER.
>
> With this new feature, the above ballooning process takes ~590ms
> resulting in an improvement of ~85%.
>
> TODO: optimize stage 1) by allocating/freeing a chunk of pages
> instead of a single page each time.
>
> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
> Cc: Amit Shah <amit.shah@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Liang Li <liliang324@xxxxxxxxx>
> Cc: Wei Wang <wei.w.wang@xxxxxxxxx>
Does this pass sparse? I see some endian-ness issues here.
> ---
> drivers/virtio/virtio_balloon.c | 351 ++++++++++++++++++++++++++++++++++++----
> 1 file changed, 323 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index f59cb4f..4416370 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -42,6 +42,10 @@
> #define OOM_VBALLOON_DEFAULT_PAGES 256
> #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>
> +#define PAGE_BMAP_SIZE (8 * PAGE_SIZE)
> +#define PFNS_PER_PAGE_BMAP (PAGE_BMAP_SIZE * BITS_PER_BYTE)
> +#define PAGE_BMAP_COUNT_MAX 32
> +
> static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
> module_param(oom_pages, int, S_IRUSR | S_IWUSR);
> MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
> @@ -50,6 +54,16 @@ MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
> static struct vfsmount *balloon_mnt;
> #endif
>
> +struct balloon_page_chunk {
> + __le64 base : 52;
> + __le64 size : 12;
> +};
> +
> +struct balloon_page_chunk_ext {
> + __le64 base;
> + __le64 size;
> +};
> +
> struct virtio_balloon {
> struct virtio_device *vdev;
> struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> @@ -67,6 +81,20 @@ struct virtio_balloon {
>
> /* Number of balloon pages we've told the Host we're not using. */
> unsigned int num_pages;
> + /* Pointer to the response header. */
> + struct virtio_balloon_resp_hdr resp_hdr;
> + /* Pointer to the start address of response data. */
> + __le64 *resp_data;
> + /* Size of response data buffer. */
> + unsigned int resp_buf_size;
> + /* Pointer offset of the response data. */
> + unsigned int resp_pos;
> + /* Bitmap used to save the pfns info */
> + unsigned long *page_bitmap[PAGE_BMAP_COUNT_MAX];
> + /* Number of split page bitmaps */
> + unsigned int nr_page_bmap;
> + /* Used to record the processed pfn range */
> + unsigned long min_pfn, max_pfn, start_pfn, end_pfn;
> /*
> * The pages we've told the Host we're not using are enqueued
> * at vb_dev_info->pages list.
> @@ -110,20 +138,180 @@ static void balloon_ack(struct virtqueue *vq)
> wake_up(&vb->acked);
> }
>
> -static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
> +static inline void init_bmap_pfn_range(struct virtio_balloon *vb)
> {
> - struct scatterlist sg;
> + vb->min_pfn = ULONG_MAX;
> + vb->max_pfn = 0;
> +}
> +
> +static inline void update_bmap_pfn_range(struct virtio_balloon *vb,
> + struct page *page)
> +{
> + unsigned long balloon_pfn = page_to_balloon_pfn(page);
> +
> + vb->min_pfn = min(balloon_pfn, vb->min_pfn);
> + vb->max_pfn = max(balloon_pfn, vb->max_pfn);
> +}
> +
> +static void extend_page_bitmap(struct virtio_balloon *vb,
> + unsigned long nr_pfn)
what exactly does this do?
> +{
> + int i, bmap_count;
> + unsigned long bmap_len;
> +
> + bmap_len = ALIGN(nr_pfn, BITS_PER_LONG) / BITS_PER_BYTE;
> + bmap_len = ALIGN(bmap_len, PAGE_BMAP_SIZE);
> + bmap_count = min((int)(bmap_len / PAGE_BMAP_SIZE),
> + PAGE_BMAP_COUNT_MAX);
> +
> + for (i = 1; i < bmap_count; i++) {
> + vb->page_bitmap[i] = kmalloc(PAGE_BMAP_SIZE, GFP_KERNEL);
> + if (vb->page_bitmap[i])
> + vb->nr_page_bmap++;
> + else
> + break;
seems to fail silently ...
> + }
> +}
> +
> +static void free_extended_page_bitmap(struct virtio_balloon *vb)
> +{
> + int i, bmap_count = vb->nr_page_bmap;
> +
> + for (i = 1; i < bmap_count; i++) {
> + kfree(vb->page_bitmap[i]);
> + vb->page_bitmap[i] = NULL;
> + vb->nr_page_bmap--;
> + }
> +}
> +
> +static void kfree_page_bitmap(struct virtio_balloon *vb)
> +{
> + int i;
> +
> + for (i = 0; i < vb->nr_page_bmap; i++)
> + kfree(vb->page_bitmap[i]);
> +}
> +
A very confusing name. pls don't start with kfree.
> +static void clear_page_bitmap(struct virtio_balloon *vb)
> +{
> + int i;
> +
> + for (i = 0; i < vb->nr_page_bmap; i++)
> + memset(vb->page_bitmap[i], 0, PAGE_BMAP_SIZE);
> +}
> +
> +static void send_resp_data(struct virtio_balloon *vb, struct virtqueue *vq,
> + bool busy_wait)
> +{
> + struct scatterlist sg[2];
> + struct virtio_balloon_resp_hdr *hdr = &vb->resp_hdr;
> unsigned int len;
>
> - sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
> + len = hdr->data_len = vb->resp_pos * sizeof(__le64);
> + sg_init_table(sg, 2);
> + sg_set_buf(&sg[0], hdr, sizeof(struct virtio_balloon_resp_hdr));
> + sg_set_buf(&sg[1], vb->resp_data, len);
> +
> + if (virtqueue_add_outbuf(vq, sg, 2, vb, GFP_KERNEL) == 0) {
!virtqueue_add_outbuf
Also how about making this header linear with pfns?
This way you can use 1 s/g and avoid mallocs.
> + virtqueue_kick(vq);
> + if (busy_wait)
> + while (!virtqueue_get_buf(vq, &len)
> + && !virtqueue_is_broken(vq))
> + cpu_relax();
> + else
> + wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> + vb->resp_pos = 0;
> + free_extended_page_bitmap(vb);
> + }
> +}
>
> - /* We should always be able to add one buffer to an empty queue. */
> - virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> - virtqueue_kick(vq);
> +static void do_set_resp_bitmap(struct virtio_balloon *vb, unsigned long base,
> + int size)
> +{
> + /* Use the extented chunk format if the size is too large */
> + if (size > (1 << VIRTIO_BALLOON_CHUNK_SIZE_SHIFT)) {
> + struct balloon_page_chunk_ext *chunk_ext =
> + (struct balloon_page_chunk_ext *)(vb->resp_data + vb->resp_pos);
> + chunk_ext->base = cpu_to_le64(base);
> + chunk_ext->size = cpu_to_le64(size);
> + vb->resp_pos += sizeof(vb->resp_pos) / sizeof(*chunk_ext);
> + } else {
> + struct balloon_page_chunk *chunk =
> + (struct balloon_page_chunk *)(vb->resp_data + vb->resp_pos);
> + chunk->base = cpu_to_le64(base);
> + chunk->size = cpu_to_le16(size);
> + vb->resp_pos += sizeof(vb->resp_pos) / sizeof(*chunk);
> + }
> +}
>
> - /* When host has read buffer, this completes via balloon_ack */
> - wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> +static void chunking_pages_from_bmap(struct virtio_balloon *vb,
> + struct virtqueue *vq,
> + unsigned long start_pfn, unsigned long *bitmap,
> + unsigned long len, bool busy_wait)
> +{
> + unsigned long pos = 0, end = len * BITS_PER_BYTE;
> +
> + while (pos < end) {
> + unsigned long one = find_next_bit(bitmap, end, pos);
> +
> + if (one < end) {
> + unsigned long chunk_size, zero;
> +
> + zero = find_next_zero_bit(bitmap, end, one + 1);
> + if (zero >= end)
> + chunk_size = end - one;
> + else
> + chunk_size = zero - one;
> + if (chunk_size) {
> + if ((vb->resp_pos + 2) * sizeof(__le64) >
> + vb->resp_buf_size)
why + 2? where does sizeof come from?
Any chance this can be cleaned up using structs sizeof etc?
or at least commented?
How am I supposed to figure out all this convoluted pointer math?
> + send_resp_data(vb, vq, busy_wait);
> + do_set_resp_bitmap(vb, start_pfn + one, chunk_size);
> + }
> + pos = one + chunk_size;
> + } else
> + break;
> + }
> +}
>
> +static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
> +{
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CHUNK_TRANSFER)) {
> + int nr_pfn, nr_used_bmap, i;
> + unsigned long start_pfn, bmap_len;
> +
> + start_pfn = vb->start_pfn;
> + nr_pfn = vb->end_pfn - start_pfn + 1;
> + nr_pfn = roundup(nr_pfn, BITS_PER_LONG);
> + nr_used_bmap = nr_pfn / PFNS_PER_PAGE_BMAP;
better name here including "page"?
And bmaps instead of bmap?
> + if (nr_pfn % PFNS_PER_PAGE_BMAP)
> + nr_used_bmap++;
Pls just use macros like ALIGN or roundup?
> + bmap_len = nr_pfn / BITS_PER_BYTE;
I guess we need to round up.
> +
> + for (i = 0; i < nr_used_bmap; i++) {
> + unsigned int bmap_size = PAGE_BMAP_SIZE;
> +
> + if (i + 1 == nr_used_bmap)
> + bmap_size = bmap_len - PAGE_BMAP_SIZE * i;
So last one is treated speacially? why?
> + chunking_pages_from_bmap(vb, vq, start_pfn + i * PFNS_PER_PAGE_BMAP,
> + vb->page_bitmap[i], bmap_size, false);
> + }
> + if (vb->resp_pos > 0)
> + send_resp_data(vb, vq, false);
> + } else {
> + struct scatterlist sg;
> + unsigned int len;
> +
> + sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
> +
> + /* We should always be able to add one buffer to an
> + * empty queue
> + */
/*
* Multi-line comments
* like this.
*/
> + virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> + virtqueue_kick(vq);
> + /* When host has read buffer, this completes via balloon_ack */
> + wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> + }
> }
>
> static void set_page_pfns(struct virtio_balloon *vb,
> @@ -138,13 +326,58 @@ static void set_page_pfns(struct virtio_balloon *vb,
> page_to_balloon_pfn(page) + i);
> }
>
> -static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> +static void set_page_bitmap(struct virtio_balloon *vb,
> + struct list_head *pages, struct virtqueue *vq)
align on ( pls.
> +{
> + unsigned long pfn, pfn_limit;
> + struct page *page;
> + bool found;
> +
> + vb->min_pfn = rounddown(vb->min_pfn, BITS_PER_LONG);
> + vb->max_pfn = roundup(vb->max_pfn, BITS_PER_LONG);
> + pfn_limit = PFNS_PER_PAGE_BMAP * vb->nr_page_bmap;
> +
> + if (vb->nr_page_bmap == 1)
> + extend_page_bitmap(vb, vb->max_pfn - vb->min_pfn + 1);
how is 1 special?
> + for (pfn = vb->min_pfn; pfn < vb->max_pfn; pfn += pfn_limit) {
> + unsigned long end_pfn;
> +
> + clear_page_bitmap(vb);
> + vb->start_pfn = pfn;
> + end_pfn = pfn;
> + found = false;
> + list_for_each_entry(page, pages, lru) {
> + unsigned long bmap_idx, bmap_pos, balloon_pfn;
> +
> + balloon_pfn = page_to_balloon_pfn(page);
> + if (balloon_pfn < pfn || balloon_pfn >= pfn + pfn_limit)
> + continue;
> + bmap_idx = (balloon_pfn - pfn) / PFNS_PER_PAGE_BMAP;
> + bmap_pos = (balloon_pfn - pfn) % PFNS_PER_PAGE_BMAP;
> + set_bit(bmap_pos, vb->page_bitmap[bmap_idx]);
> + if (balloon_pfn > end_pfn)
> + end_pfn = balloon_pfn;
> + found = true;
> + }
> + if (found) {
> + vb->end_pfn = end_pfn;
> + tell_host(vb, vq);
> + }
> + }
> +}
> +
> +static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num)
> {
> struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> - unsigned num_allocated_pages;
> + unsigned int num_allocated_pages;
> + bool chunking = virtio_has_feature(vb->vdev,
> + VIRTIO_BALLOON_F_CHUNK_TRANSFER);
>
> - /* We can only do one array worth at a time. */
> - num = min(num, ARRAY_SIZE(vb->pfns));
> + if (chunking)
> + init_bmap_pfn_range(vb);
> + else
> + /* We can only do one array worth at a time. */
> + num = min(num, ARRAY_SIZE(vb->pfns));
>
> mutex_lock(&vb->balloon_lock);
> for (vb->num_pfns = 0; vb->num_pfns < num;
> @@ -159,7 +392,10 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> msleep(200);
> break;
> }
> - set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> + if (chunking)
> + update_bmap_pfn_range(vb, page);
> + else
> + set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
> if (!virtio_has_feature(vb->vdev,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> @@ -168,8 +404,13 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
>
> num_allocated_pages = vb->num_pfns;
> /* Did we get any? */
> - if (vb->num_pfns != 0)
> - tell_host(vb, vb->inflate_vq);
> + if (vb->num_pfns != 0) {
> + if (chunking)
> + set_page_bitmap(vb, &vb_dev_info->pages,
> + vb->inflate_vq);
> + else
> + tell_host(vb, vb->inflate_vq);
> + }
> mutex_unlock(&vb->balloon_lock);
>
> return num_allocated_pages;
> @@ -189,15 +430,20 @@ static void release_pages_balloon(struct virtio_balloon *vb,
> }
> }
>
> -static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
> +static unsigned int leak_balloon(struct virtio_balloon *vb, size_t num)
> {
> - unsigned num_freed_pages;
> + unsigned int num_freed_pages;
> struct page *page;
> struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> LIST_HEAD(pages);
> + bool chunking = virtio_has_feature(vb->vdev,
> + VIRTIO_BALLOON_F_CHUNK_TRANSFER);
Align on ( pls.
>
> - /* We can only do one array worth at a time. */
> - num = min(num, ARRAY_SIZE(vb->pfns));
> + if (chunking)
> + init_bmap_pfn_range(vb);
> + else
> + /* We can only do one array worth at a time. */
> + num = min(num, ARRAY_SIZE(vb->pfns));
>
> mutex_lock(&vb->balloon_lock);
> /* We can't release more pages than taken */
> @@ -207,7 +453,10 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
> page = balloon_page_dequeue(vb_dev_info);
> if (!page)
> break;
> - set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> + if (chunking)
> + update_bmap_pfn_range(vb, page);
> + else
> + set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
> list_add(&page->lru, &pages);
> vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> }
> @@ -218,8 +467,12 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
> * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> * is true, we *have* to do it in this order
> */
> - if (vb->num_pfns != 0)
> - tell_host(vb, vb->deflate_vq);
> + if (vb->num_pfns != 0) {
> + if (chunking)
> + set_page_bitmap(vb, &pages, vb->deflate_vq);
> + else
> + tell_host(vb, vb->deflate_vq);
> + }
> release_pages_balloon(vb, &pages);
> mutex_unlock(&vb->balloon_lock);
> return num_freed_pages;
> @@ -431,6 +684,18 @@ static int init_vqs(struct virtio_balloon *vb)
> }
>
> #ifdef CONFIG_BALLOON_COMPACTION
> +static void tell_host_one_page(struct virtio_balloon *vb,
> + struct virtqueue *vq, struct page *page)
> +{
> + __le64 *chunk;
> +
> + chunk = vb->resp_data + vb->resp_pos;
> + *chunk = cpu_to_le64((page_to_pfn(page) <<
> + VIRTIO_BALLOON_CHUNK_SIZE_SHIFT) | 1);
> + vb->resp_pos++;
> + send_resp_data(vb, vq, false);
> +}
> +
> /*
> * virtballoon_migratepage - perform the balloon page migration on behalf of
> * a compation thread. (called under page lock)
> @@ -455,6 +720,8 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
> struct virtio_balloon *vb = container_of(vb_dev_info,
> struct virtio_balloon, vb_dev_info);
> unsigned long flags;
> + bool chunking = virtio_has_feature(vb->vdev,
> + VIRTIO_BALLOON_F_CHUNK_TRANSFER);
>
> /*
> * In order to avoid lock contention while migrating pages concurrently
> @@ -475,15 +742,23 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
> vb_dev_info->isolated_pages--;
> __count_vm_event(BALLOON_MIGRATE);
> spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
> - vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> - set_page_pfns(vb, vb->pfns, newpage);
> - tell_host(vb, vb->inflate_vq);
> + if (chunking)
> + tell_host_one_page(vb, vb->inflate_vq, newpage);
> + else {
Ad {} around 1st block too pls.
> + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> + set_page_pfns(vb, vb->pfns, newpage);
> + tell_host(vb, vb->inflate_vq);
> + }
>
> /* balloon's page migration 2nd step -- deflate "page" */
> balloon_page_delete(page);
> - vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> - set_page_pfns(vb, vb->pfns, page);
> - tell_host(vb, vb->deflate_vq);
> + if (chunking)
> + tell_host_one_page(vb, vb->deflate_vq, page);
and here
> + else {
> + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> + set_page_pfns(vb, vb->pfns, page);
> + tell_host(vb, vb->deflate_vq);
> + }
>
> mutex_unlock(&vb->balloon_lock);
>
> @@ -533,6 +808,21 @@ static int virtballoon_probe(struct virtio_device *vdev)
> spin_lock_init(&vb->stop_update_lock);
> vb->stop_update = false;
> vb->num_pages = 0;
> +
> + vb->page_bitmap[0] = kmalloc(PAGE_BMAP_SIZE, GFP_KERNEL);
> + if (!vb->page_bitmap[0]) {
> + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_CHUNK_TRANSFER);
> + } else {
> + vb->nr_page_bmap = 1;
> + vb->resp_data = kmalloc(PAGE_BMAP_SIZE, GFP_KERNEL);
> + if (!vb->resp_data) {
> + __virtio_clear_bit(vdev,
> + VIRTIO_BALLOON_F_CHUNK_TRANSFER);
align on ( pls
> + kfree(vb->page_bitmap[0]);
> + }
> + }
> + vb->resp_pos = 0;
> + vb->resp_buf_size = PAGE_BMAP_SIZE;
> mutex_init(&vb->balloon_lock);
> init_waitqueue_head(&vb->acked);
> vb->vdev = vdev;
> @@ -578,6 +868,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
> out_del_vqs:
> vdev->config->del_vqs(vdev);
> out_free_vb:
> + kfree(vb->resp_data);
> + kfree_page_bitmap(vb);
> kfree(vb);
> out:
> return err;
> @@ -611,6 +903,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
> remove_common(vb);
> if (vb->vb_dev_info.inode)
> iput(vb->vb_dev_info.inode);
> + kfree_page_bitmap(vb);
> + kfree(vb->resp_data);
> kfree(vb);
> }
>
> @@ -649,6 +943,7 @@ static unsigned int features[] = {
> VIRTIO_BALLOON_F_MUST_TELL_HOST,
> VIRTIO_BALLOON_F_STATS_VQ,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> + VIRTIO_BALLOON_F_CHUNK_TRANSFER,
> };
>
> static struct virtio_driver virtio_balloon_driver = {
> --
> 2.7.4
