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Subject: Re: [PATCH v10 3/6] virtio-balloon: VIRTIO_BALLOON_F_PAGE_CHUNKS


On Thu, May 04, 2017 at 04:50:12PM +0800, Wei Wang wrote:
> Add a new feature, VIRTIO_BALLOON_F_PAGE_CHUNKS, which enables
> the transfer of the ballooned (i.e. inflated/deflated) pages in
> chunks to the host.
> 
> The implementation of the previous virtio-balloon is not very
> efficient, because the ballooned 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 transferring pages to the host in
> chunks. A chunk consists of guest physically continuous pages.
> When the pages are packed into a chunk, they are converted into
> balloon page size (4KB) pages. A chunk 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 4KB balloon size
> pages). A chunk is formatted as below:
> --------------------------------------------------------
> |                 Base (52 bit)        | Rsvd (12 bit) |
> --------------------------------------------------------
> --------------------------------------------------------
> |                 Size (52 bit)        | Rsvd (12 bit) |
> --------------------------------------------------------
> 
> By doing so, step 4) can also be optimized by doing address
> translation and madvise() in chunks rather than page by page.
> 
> 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: Wei Wang <wei.w.wang@intel.com>
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>


This is much cleaner, thanks. It might be even better to
have wrappers that put array and its size in a struct
and manage that struct, but I won't require this for
submission.



> ---
>  drivers/virtio/virtio_balloon.c     | 407 +++++++++++++++++++++++++++++++++---
>  include/uapi/linux/virtio_balloon.h |  14 ++
>  2 files changed, 396 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index ecb64e9..df16912 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -43,6 +43,20 @@
>  #define OOM_VBALLOON_DEFAULT_PAGES 256
>  #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>  
> +/* The size of one page_bmap used to record inflated/deflated pages. */
> +#define VIRTIO_BALLOON_PAGE_BMAP_SIZE	(8 * PAGE_SIZE)
> +/*
> + * Callulates how many pfns can a page_bmap record. A bit corresponds to a
> + * page of PAGE_SIZE.
> + */
> +#define VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP \
> +	(VIRTIO_BALLOON_PAGE_BMAP_SIZE * BITS_PER_BYTE)
> +
> +/* The number of page_bmap to allocate by default. */
> +#define VIRTIO_BALLOON_PAGE_BMAP_DEFAULT_NUM	1
> +/* The maximum number of page_bmap that can be allocated. */
> +#define VIRTIO_BALLOON_PAGE_BMAP_MAX_NUM	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");
> @@ -51,6 +65,11 @@ MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
>  static struct vfsmount *balloon_mnt;
>  #endif
>  
> +/* Maximum number of page chunks */
> +#define VIRTIO_BALLOON_MAX_PAGE_CHUNKS ((8 * PAGE_SIZE - \
> +			sizeof(struct virtio_balloon_page_chunk)) / \
> +			sizeof(struct virtio_balloon_page_chunk_entry))
> +
>  struct virtio_balloon {
>  	struct virtio_device *vdev;
>  	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> @@ -79,6 +98,12 @@ struct virtio_balloon {
>  	/* Synchronize access/update to this struct virtio_balloon elements */
>  	struct mutex balloon_lock;
>  
> +	/* Buffer for chunks of ballooned pages. */
> +	struct virtio_balloon_page_chunk *balloon_page_chunk;
> +
> +	/* Bitmap used to record pages. */
> +	unsigned long *page_bmap[VIRTIO_BALLOON_PAGE_BMAP_MAX_NUM];
> +
>  	/* The array of pfns we tell the Host about. */
>  	unsigned int num_pfns;
>  	__virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
> @@ -111,6 +136,136 @@ static void balloon_ack(struct virtqueue *vq)
>  	wake_up(&vb->acked);
>  }
>  
> +/* Update pfn_max and pfn_min according to the pfn of page */
> +static inline void update_pfn_range(struct virtio_balloon *vb,
> +				    struct page *page,
> +				    unsigned long *pfn_min,
> +				    unsigned long *pfn_max)
> +{
> +	unsigned long pfn = page_to_pfn(page);
> +
> +	*pfn_min = min(pfn, *pfn_min);
> +	*pfn_max = max(pfn, *pfn_max);
> +}
> +
> +static unsigned int extend_page_bmap_size(struct virtio_balloon *vb,
> +					  unsigned long pfn_num)
> +{
> +	unsigned int i, bmap_num, allocated_bmap_num;
> +	unsigned long bmap_len;
> +
> +	allocated_bmap_num = VIRTIO_BALLOON_PAGE_BMAP_DEFAULT_NUM;
> +	bmap_len = ALIGN(pfn_num, BITS_PER_LONG) / BITS_PER_BYTE;
> +	bmap_len = roundup(bmap_len, VIRTIO_BALLOON_PAGE_BMAP_SIZE);
> +	/*
> +	 * VIRTIO_BALLOON_PAGE_BMAP_SIZE is the size of one page_bmap, so
> +	 * divide it to calculate how many page_bmap that we need.
> +	 */
> +	bmap_num = (unsigned int)(bmap_len / VIRTIO_BALLOON_PAGE_BMAP_SIZE);
> +	/* The number of page_bmap

... arrays ...

> to allocate should not exceed the max */
> +	bmap_num = min_t(unsigned int, VIRTIO_BALLOON_PAGE_BMAP_MAX_NUM,
> +			 bmap_num);
> +
> +	for (i = VIRTIO_BALLOON_PAGE_BMAP_DEFAULT_NUM; i < bmap_num; i++) {
> +		vb->page_bmap[i] = kmalloc(VIRTIO_BALLOON_PAGE_BMAP_SIZE,
> +					   GFP_KERNEL);
> +		if (vb->page_bmap[i])
> +			allocated_bmap_num++;
> +		else
> +			break;
> +	}
> +
> +	return allocated_bmap_num;
> +}
> +
> +static void free_extended_page_bmap(struct virtio_balloon *vb,
> +				    unsigned int page_bmap_num)
> +{
> +	unsigned int i;
> +
> +	for (i = VIRTIO_BALLOON_PAGE_BMAP_DEFAULT_NUM; i < page_bmap_num;
> +	     i++) {
> +		kfree(vb->page_bmap[i]);
> +		vb->page_bmap[i] = NULL;
> +		page_bmap_num--;
> +	}
> +}
> +
> +static void clear_page_bmap(struct virtio_balloon *vb,
> +			    unsigned int page_bmap_num)
> +{
> +	int i;
> +
> +	for (i = 0; i < page_bmap_num; i++)
> +		memset(vb->page_bmap[i], 0, VIRTIO_BALLOON_PAGE_BMAP_SIZE);
> +}
> +
> +static void send_page_chunks(struct virtio_balloon *vb, struct virtqueue *vq)
> +{
> +	struct scatterlist sg;
> +	struct virtio_balloon_page_chunk *chunk;
> +	unsigned int len;
> +
> +	chunk = vb->balloon_page_chunk;
> +	len = sizeof(__le64) +
> +	      le64_to_cpu(chunk->chunk_num) *
> +	      sizeof(struct virtio_balloon_page_chunk_entry);
> +	sg_init_one(&sg, chunk, len);
> +	if (!virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL)) {
> +		virtqueue_kick(vq);
> +		wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> +		chunk->chunk_num = 0;
> +	}
> +}
> +
> +/* Add a chunk entry to the buffer. */
> +static void add_one_chunk(struct virtio_balloon *vb, struct virtqueue *vq,
> +			  u64 base, u64 size)
> +{
> +	struct virtio_balloon_page_chunk *chunk = vb->balloon_page_chunk;
> +	struct virtio_balloon_page_chunk_entry *entry;
> +	uint64_t chunk_num = le64_to_cpu(chunk->chunk_num);
> +
> +	entry = &chunk->entry[chunk_num];
> +	entry->base = cpu_to_le64(base << VIRTIO_BALLOON_CHUNK_BASE_SHIFT);
> +	entry->size = cpu_to_le64(size << VIRTIO_BALLOON_CHUNK_SIZE_SHIFT);
> +	chunk->chunk_num = cpu_to_le64(++chunk_num);
> +	if (chunk_num == VIRTIO_BALLOON_MAX_PAGE_CHUNKS)
> +		send_page_chunks(vb, vq);
> +}
> +
> +static void convert_bmap_to_chunks(struct virtio_balloon *vb,
> +				   struct virtqueue *vq,
> +				   unsigned long *bmap,
> +				   unsigned long pfn_start,
> +				   unsigned long size)
> +{
> +	unsigned long next_one, next_zero, chunk_size, pos = 0;
> +
> +	while (pos < size) {
> +		next_one = find_next_bit(bmap, size, pos);
> +		/*
> +		 * No "1" bit found, which means that there is no pfn
> +		 * recorded in the rest of this bmap.
> +		 */
> +		if (next_one == size)
> +			break;
> +		next_zero = find_next_zero_bit(bmap, size, next_one + 1);
> +		/*
> +		 * A bit in page_bmap corresponds to a page of PAGE_SIZE.
> +		 * Convert it to be pages of 4KB balloon page size when
> +		 * adding it to a chunk.
> +		 */
> +		chunk_size = (next_zero - next_one) *
> +			     VIRTIO_BALLOON_PAGES_PER_PAGE;
> +		if (chunk_size) {
> +			add_one_chunk(vb, vq, pfn_start + next_one,
> +				      chunk_size);
> +			pos += next_zero + 1;
> +		}
> +	}
> +}
> +
>  static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
>  {
>  	struct scatterlist sg;
> @@ -124,7 +279,33 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
>  
>  	/* When host has read buffer, this completes via balloon_ack */
>  	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> +}
> +
> +static void tell_host_from_page_bmap(struct virtio_balloon *vb,
> +				     struct virtqueue *vq,
> +				     unsigned long pfn_start,
> +				     unsigned long pfn_end,
> +				     unsigned int page_bmap_num)
> +{
> +	unsigned long i, pfn_num;
>  
> +	for (i = 0; i < page_bmap_num; i++) {
> +		/*
> +		 * For the last page_bmap, only the remaining number of pfns
> +		 * need to be searched rather than the entire page_bmap.
> +		 */
> +		if (i + 1 == page_bmap_num)
> +			pfn_num = (pfn_end - pfn_start) %
> +				  VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP;
> +		else
> +			pfn_num = VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP;
> +
> +		convert_bmap_to_chunks(vb, vq, vb->page_bmap[i], pfn_start +
> +				       i * VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP,
> +				       pfn_num);
> +	}
> +	if (le64_to_cpu(vb->balloon_page_chunk->chunk_num) > 0)
> +		send_page_chunks(vb, vq);
>  }
>  
>  static void set_page_pfns(struct virtio_balloon *vb,
> @@ -141,13 +322,88 @@ static void set_page_pfns(struct virtio_balloon *vb,
>  					  page_to_balloon_pfn(page) + i);
>  }
>  
> +/*
> + * Send ballooned pages in chunks to host.
> + * The ballooned pages are recorded in page bitmaps. Each bit in a bitmap
> + * corresponds to a page of PAGE_SIZE. The page bitmaps are searched for
> + * continuous "1" bits, which correspond to continuous pages, to chunk.
> + * When packing those continuous pages into chunks, pages are converted into
> + * 4KB balloon pages.
> + *
> + * pfn_max and pfn_min form the range of pfns that need to use page bitmaps to
> + * record. If the range is too large to be recorded into the allocated page
> + * bitmaps, the page bitmaps are used multiple times to record the entire
> + * range of pfns.
> + */
> +static void tell_host_page_chunks(struct virtio_balloon *vb,
> +				  struct list_head *pages,
> +				  struct virtqueue *vq,
> +				  unsigned long pfn_max,
> +				  unsigned long pfn_min)
> +{
> +	/*
> +	 * The pfn_start and pfn_end form the range of pfns that the allocated
> +	 * page_bmap can record in each round.
> +	 */
> +	unsigned long pfn_start, pfn_end;
> +	/* Total number of allocated page_bmap

arrays

> */
> +	unsigned int page_bmap_num;
> +	struct page *page;
> +	bool found;
> +
> +	/*
> +	 * In the case that one page_bmap is not sufficient to record the pfn
> +	 * range, page_bmap will be extended by allocating more numbers of
> +	 * page_bmap.
> +	 */
> +	page_bmap_num = extend_page_bmap_size(vb, pfn_max - pfn_min + 1);
> +
> +	/* Start from the beginning of the whole pfn range */
> +	pfn_start = pfn_min;
> +	while (pfn_start < pfn_max) {
> +		pfn_end = pfn_start +
> +			  VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP * page_bmap_num;
> +		pfn_end = pfn_end < pfn_max ? pfn_end : pfn_max;
> +		clear_page_bmap(vb, page_bmap_num);
> +		found = false;
> +
> +		list_for_each_entry(page, pages, lru) {
> +			unsigned long bmap_idx, bmap_pos, this_pfn;
> +
> +			this_pfn = page_to_pfn(page);
> +			if (this_pfn < pfn_start || this_pfn > pfn_end)
> +				continue;
> +			bmap_idx = (this_pfn - pfn_start) /
> +				   VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP;
> +			bmap_pos = (this_pfn - pfn_start) %
> +				   VIRTIO_BALLOON_PFNS_PER_PAGE_BMAP;
> +			set_bit(bmap_pos, vb->page_bmap[bmap_idx]);
> +
> +			found = true;
> +		}
> +		if (found)
> +			tell_host_from_page_bmap(vb, vq, pfn_start, pfn_end,
> +						 page_bmap_num);
> +		/*
> +		 * Start the next round when pfn_start and pfn_end couldn't
> +		 * cover the whole pfn range given by pfn_max and pfn_min.
> +		 */
> +		pfn_start = pfn_end;
> +	}
> +	free_extended_page_bmap(vb, page_bmap_num);
> +}
> +
>  static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
>  {
>  	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
>  	unsigned num_allocated_pages;
> +	bool chunking = virtio_has_feature(vb->vdev,
> +					   VIRTIO_BALLOON_F_PAGE_CHUNKS);
> +	unsigned long pfn_max = 0, pfn_min = ULONG_MAX;
>  
>  	/* We can only do one array worth at a time. */
> -	num = min(num, ARRAY_SIZE(vb->pfns));
> +	if (!chunking)
> +		num = min(num, ARRAY_SIZE(vb->pfns));
>  
>  	mutex_lock(&vb->balloon_lock);
>  	for (vb->num_pfns = 0; vb->num_pfns < num;
> @@ -162,7 +418,10 @@ 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_pfn_range(vb, page, &pfn_max, &pfn_min);
> +		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))
> @@ -171,8 +430,14 @@ 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)
> +			tell_host_page_chunks(vb, &vb_dev_info->pages,
> +					      vb->inflate_vq,
> +					      pfn_max, pfn_min);
> +		else
> +			tell_host(vb, vb->inflate_vq);
> +	}
>  	mutex_unlock(&vb->balloon_lock);
>  
>  	return num_allocated_pages;
> @@ -198,9 +463,13 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
>  	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_PAGE_CHUNKS);
> +	unsigned long pfn_max = 0, pfn_min = ULONG_MAX;
>  
> -	/* We can only do one array worth at a time. */
> -	num = min(num, ARRAY_SIZE(vb->pfns));
> +	/* Traditionally, we can only do one array worth at a time. */
> +	if (!chunking)
> +		num = min(num, ARRAY_SIZE(vb->pfns));
>  
>  	mutex_lock(&vb->balloon_lock);
>  	/* We can't release more pages than taken */
> @@ -210,7 +479,10 @@ 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_pfn_range(vb, page, &pfn_max, &pfn_min);
> +		else
> +			set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
>  		list_add(&page->lru, &pages);
>  		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
>  	}
> @@ -221,8 +493,13 @@ 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)
> +			tell_host_page_chunks(vb, &pages, vb->deflate_vq,
> +					      pfn_max, pfn_min);
> +		else
> +			tell_host(vb, vb->deflate_vq);
> +	}
>  	release_pages_balloon(vb, &pages);
>  	mutex_unlock(&vb->balloon_lock);
>  	return num_freed_pages;
> @@ -442,6 +719,14 @@ 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)
> +{
> +	add_one_chunk(vb, vq, page_to_pfn(page),
> +		      VIRTIO_BALLOON_PAGES_PER_PAGE);
> +}
> +
>  /*
>   * virtballoon_migratepage - perform the balloon page migration on behalf of
>   *			     a compation thread.     (called under page lock)
> @@ -465,6 +750,8 @@ 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);
> +	bool chunking = virtio_has_feature(vb->vdev,
> +					   VIRTIO_BALLOON_F_PAGE_CHUNKS);
>  	unsigned long flags;
>  
>  	/*
> @@ -486,16 +773,22 @@ 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 {
> +		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);
> +	} 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);
>  
>  	put_page(page); /* balloon reference */
> @@ -522,9 +815,75 @@ static struct file_system_type balloon_fs = {
>  
>  #endif /* CONFIG_BALLOON_COMPACTION */
>  
> +static void free_page_bmap(struct virtio_balloon *vb)
> +{
> +	int i;
> +
> +	for (i = 0; i < VIRTIO_BALLOON_PAGE_BMAP_DEFAULT_NUM; i++) {
> +		kfree(vb->page_bmap[i]);
> +		vb->page_bmap[i] = NULL;
> +	}
> +}
> +
> +static int balloon_page_chunk_init(struct virtio_balloon *vb)
> +{
> +	int i;
> +
> +	vb->balloon_page_chunk = kmalloc(sizeof(__le64) +
> +			sizeof(struct virtio_balloon_page_chunk_entry) *
> +			VIRTIO_BALLOON_MAX_PAGE_CHUNKS, GFP_KERNEL);
> +	if (!vb->balloon_page_chunk)
> +		goto err_page_chunk;
> +
> +	/*
> +	 * The default number of page_bmaps are allocated. More may be
> +	 * allocated on demand.
> +	 */
> +	for (i = 0; i < VIRTIO_BALLOON_PAGE_BMAP_DEFAULT_NUM; i++) {
> +		vb->page_bmap[i] = kmalloc(VIRTIO_BALLOON_PAGE_BMAP_SIZE,
> +					   GFP_KERNEL);
> +		if (!vb->page_bmap[i])
> +			goto err_page_bmap;
> +	}
> +
> +	return 0;
> +err_page_bmap:
> +	free_page_bmap(vb);
> +	kfree(vb->balloon_page_chunk);
> +	vb->balloon_page_chunk = NULL;
> +err_page_chunk:
> +	__virtio_clear_bit(vb->vdev, VIRTIO_BALLOON_F_PAGE_CHUNKS);
> +	dev_warn(&vb->vdev->dev, "%s: failed\n", __func__);
> +	return -ENOMEM;
> +}
> +
> +static int virtballoon_validate(struct virtio_device *vdev)
> +{
> +	struct virtio_balloon *vb = NULL;
> +	int err;
> +
> +	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
> +	if (!vb) {
> +		err = -ENOMEM;
> +		goto err_vb;
> +	}
> +
> +	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_CHUNKS)) {
> +		err = balloon_page_chunk_init(vb);
> +		if (err < 0)
> +			goto err_page_chunk;
> +	}
> +
> +	return 0;
> +err_page_chunk:
> +	kfree(vb);
> +err_vb:
> +	return err;
> +}
> +
>  static int virtballoon_probe(struct virtio_device *vdev)
>  {
> -	struct virtio_balloon *vb;
> +	struct virtio_balloon *vb = vdev->priv;
>  	int err;
>  
>  	if (!vdev->config->get) {
> @@ -533,17 +892,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  		return -EINVAL;
>  	}
>  
> -	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
> -	if (!vb) {
> -		err = -ENOMEM;
> -		goto out;
> -	}
> -
>  	INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
>  	INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
>  	spin_lock_init(&vb->stop_update_lock);
>  	vb->stop_update = false;
>  	vb->num_pages = 0;
> +
>  	mutex_init(&vb->balloon_lock);
>  	init_waitqueue_head(&vb->acked);
>  	vb->vdev = vdev;
> @@ -590,7 +944,6 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  	vdev->config->del_vqs(vdev);
>  out_free_vb:
>  	kfree(vb);
> -out:
>  	return err;
>  }
>  
> @@ -620,6 +973,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
>  	cancel_work_sync(&vb->update_balloon_stats_work);
>  
>  	remove_common(vb);
> +	free_page_bmap(vb);
> +	kfree(vb->balloon_page_chunk);
>  #ifdef CONFIG_BALLOON_COMPACTION
>  	if (vb->vb_dev_info.inode)
>  		iput(vb->vb_dev_info.inode);
> @@ -664,6 +1019,7 @@ static unsigned int features[] = {
>  	VIRTIO_BALLOON_F_MUST_TELL_HOST,
>  	VIRTIO_BALLOON_F_STATS_VQ,
>  	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> +	VIRTIO_BALLOON_F_PAGE_CHUNKS,
>  };
>  
>  static struct virtio_driver virtio_balloon_driver = {
> @@ -674,6 +1030,7 @@ static struct virtio_driver virtio_balloon_driver = {
>  	.id_table =	id_table,
>  	.probe =	virtballoon_probe,
>  	.remove =	virtballoon_remove,
> +	.validate =	virtballoon_validate,
>  	.config_changed = virtballoon_changed,
>  #ifdef CONFIG_PM_SLEEP
>  	.freeze	=	virtballoon_freeze,
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 343d7dd..d532ed16 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -34,6 +34,7 @@
>  #define VIRTIO_BALLOON_F_MUST_TELL_HOST	0 /* Tell before reclaiming pages */
>  #define VIRTIO_BALLOON_F_STATS_VQ	1 /* Memory Stats virtqueue */
>  #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM	2 /* Deflate balloon on OOM */
> +#define VIRTIO_BALLOON_F_PAGE_CHUNKS	3 /* Inflate/Deflate pages in chunks */
>  
>  /* Size of a PFN in the balloon interface. */
>  #define VIRTIO_BALLOON_PFN_SHIFT 12
> @@ -82,4 +83,17 @@ struct virtio_balloon_stat {
>  	__virtio64 val;
>  } __attribute__((packed));
>  
> +#define VIRTIO_BALLOON_CHUNK_BASE_SHIFT 12
> +#define VIRTIO_BALLOON_CHUNK_SIZE_SHIFT 12
> +struct virtio_balloon_page_chunk_entry {
> +	__le64 base;
> +	__le64 size;
> +};
> +
> +struct virtio_balloon_page_chunk {
> +	/* Number of chunks in the payload */
> +	__le64 chunk_num;
> +	struct virtio_balloon_page_chunk_entry entry[];
> +};
> +
>  #endif /* _LINUX_VIRTIO_BALLOON_H */
> -- 
> 2.7.4


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