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SubjectRe: [RESEND PATCH v3 kernel 4/7] virtio-balloon: speed up inflate/deflate process
On Fri, Oct 21, 2016 at 02:24:37PM +0800, Liang Li wrote:
> The implementation of the current virtio-balloon is not very
> efficient, the time spends on different stages of inflating
> the balloon to 7GB of a 8GB idle guest:
>
> a. allocating pages (6.5%)
> b. sending PFNs to host (68.3%)
> c. address translation (6.1%)
> d. madvise (19%)
>
> It takes about 4126ms for the inflating process to complete.
> Debugging shows that the bottle neck are the stage b and stage d.
>
> If using a bitmap to send the page info instead of the PFNs, we
> can reduce the overhead in stage b quite a lot. Furthermore, we
> can do the address translation and call madvise() with a bulk of
> RAM pages, instead of the current page per page way, the overhead
> of stage c and stage d can also be reduced a lot.
>
> This patch is the kernel side implementation which is intended to
> speed up the inflating & deflating process by adding a new feature
> to the virtio-balloon device. With this new feature, inflating the
> balloon to 7GB of a 8GB idle guest only takes 590ms, the
> performance improvement is about 85%.
>
> TODO: optimize stage a by allocating/freeing a chunk of pages
> instead of a single page at a time.
>
> Signed-off-by: Liang Li <liang.z.li@intel.com>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
> Cc: Amit Shah <amit.shah@redhat.com>
> ---
> drivers/virtio/virtio_balloon.c | 233 +++++++++++++++++++++++++++++++++++-----
> 1 file changed, 209 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 59ffe5a..c31839c 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 BALLOON_BMAP_SIZE (8 * PAGE_SIZE)
> +#define PFNS_PER_BMAP (BALLOON_BMAP_SIZE * BITS_PER_BYTE)
> +#define BALLOON_BMAP_COUNT 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");
> @@ -67,6 +71,13 @@ struct virtio_balloon {
>
> /* Number of balloon pages we've told the Host we're not using. */
> unsigned int num_pages;
> + /* Pointer of the bitmap header. */
> + void *bmap_hdr;
> + /* Bitmap and bitmap count used to tell the host the pages */
> + unsigned long *page_bitmap[BALLOON_BMAP_COUNT];
> + 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.
> @@ -110,16 +121,66 @@ static void balloon_ack(struct virtqueue *vq)
> wake_up(&vb->acked);
> }
>
> +static inline void init_pfn_range(struct virtio_balloon *vb)
> +{
> + vb->min_pfn = ULONG_MAX;
> + vb->max_pfn = 0;
> +}
> +
> +static inline void update_pfn_range(struct virtio_balloon *vb,
> + struct page *page)
> +{
> + unsigned long balloon_pfn = page_to_balloon_pfn(page);
> +
> + if (balloon_pfn < vb->min_pfn)
> + vb->min_pfn = balloon_pfn;
> + if (balloon_pfn > vb->max_pfn)
> + vb->max_pfn = balloon_pfn;
> +}
> +

rename to hint these are all bitmap related.


> static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
> {
> - struct scatterlist sg;
> - unsigned int len;
> + struct scatterlist sg, sg2[BALLOON_BMAP_COUNT + 1];
> + unsigned int len, i;
> +
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP)) {
> + struct balloon_bmap_hdr *hdr = vb->bmap_hdr;
> + unsigned long bmap_len;
> + int nr_pfn, nr_used_bmap, nr_buf;
> +
> + nr_pfn = vb->end_pfn - vb->start_pfn + 1;
> + nr_pfn = roundup(nr_pfn, BITS_PER_LONG);
> + nr_used_bmap = nr_pfn / PFNS_PER_BMAP;
> + bmap_len = nr_pfn / BITS_PER_BYTE;
> + nr_buf = nr_used_bmap + 1;
> +
> + /* cmd, reserved and req_id are init to 0, unused here */
> + hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
> + hdr->start_pfn = cpu_to_virtio64(vb->vdev, vb->start_pfn);
> + hdr->bmap_len = cpu_to_virtio64(vb->vdev, bmap_len);
> + sg_init_table(sg2, nr_buf);
> + sg_set_buf(&sg2[0], hdr, sizeof(struct balloon_bmap_hdr));
> + for (i = 0; i < nr_used_bmap; i++) {
> + unsigned int buf_len = BALLOON_BMAP_SIZE;
> +
> + if (i + 1 == nr_used_bmap)
> + buf_len = bmap_len - BALLOON_BMAP_SIZE * i;
> + sg_set_buf(&sg2[i + 1], vb->page_bitmap[i], buf_len);
> + }
>
> - sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
> + while (vq->num_free < nr_buf)
> + msleep(2);


What's going on here? Who is expected to update num_free?



> + if (virtqueue_add_outbuf(vq, sg2, nr_buf, vb, GFP_KERNEL) == 0)
> + virtqueue_kick(vq);
>
> - /* 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);
> + } else {
> + 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. */

Pls use a multiple comment style consistent with kernel coding style.

> + 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));
> @@ -138,13 +199,93 @@ 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 extend_page_bitmap(struct virtio_balloon *vb)
> +{
> + int i;
> + unsigned long bmap_len, bmap_count;
> +
> + bmap_len = ALIGN(get_max_pfn(), BITS_PER_LONG) / BITS_PER_BYTE;
> + bmap_count = bmap_len / BALLOON_BMAP_SIZE;
> + if (bmap_len % BALLOON_BMAP_SIZE)
> + bmap_count++;
> + if (bmap_count > BALLOON_BMAP_COUNT)
> + bmap_count = BALLOON_BMAP_COUNT;
> +

This is doing simple things in tricky ways.
Please use macros such as ALIGN and max instead of if.


> + for (i = 1; i < bmap_count; i++) {

why 1?

> + vb->page_bitmap[i] = kmalloc(BALLOON_BMAP_SIZE, GFP_ATOMIC);

why GFP_ATOMIC?
and what will free the previous buffer?


> + if (vb->page_bitmap[i])
> + vb->nr_page_bmap++;
> + else
> + break;

and what will happen then?

> + }
> +}
> +
> +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]);
> +}
> +
> +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, BALLOON_BMAP_SIZE);
> +}
> +
> +static void set_page_bitmap(struct virtio_balloon *vb,
> + struct list_head *pages, struct virtqueue *vq)
> +{
> + unsigned long pfn, pfn_limit;
> + struct page *page;
> + bool found;
> + int bmap_idx;
> +
> + vb->min_pfn = rounddown(vb->min_pfn, BITS_PER_LONG);
> + vb->max_pfn = roundup(vb->max_pfn, BITS_PER_LONG);
> + pfn_limit = PFNS_PER_BMAP * vb->nr_page_bmap;
> +
> + 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 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_BMAP;
> + pos = (balloon_pfn - pfn) % PFNS_PER_BMAP;
> + set_bit(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,
> + bool use_bmap)
> {
> struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> - unsigned num_allocated_pages;
> + unsigned int num_allocated_pages;
>
> - /* We can only do one array worth at a time. */
> - num = min(num, ARRAY_SIZE(vb->pfns));
> + if (use_bmap)
> + init_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 +300,10 @@ 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 (use_bmap)
> + update_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 +312,13 @@ 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 (use_bmap)
> + 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 +338,19 @@ 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,
> + bool use_bmap)

this is just a feature bit - why not get it internally?

> {
> - 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);
>
> - /* We can only do one array worth at a time. */
> - num = min(num, ARRAY_SIZE(vb->pfns));
> + if (use_bmap)
> + init_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 +360,10 @@ 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 (use_bmap)
> + update_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 +374,14 @@ 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 (use_bmap)
> + set_page_bitmap(vb, &pages, vb->deflate_vq);
> + else
> + tell_host(vb, vb->deflate_vq);
> +
> + release_pages_balloon(vb, &pages);
> + }
> release_pages_balloon(vb, &pages);
> mutex_unlock(&vb->balloon_lock);
> return num_freed_pages;
> @@ -354,13 +516,15 @@ static int virtballoon_oom_notify(struct notifier_block *self,
> struct virtio_balloon *vb;
> unsigned long *freed;
> unsigned num_freed_pages;
> + bool use_bmap;
>
> vb = container_of(self, struct virtio_balloon, nb);
> if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> return NOTIFY_OK;
>
> freed = parm;
> - num_freed_pages = leak_balloon(vb, oom_pages);
> + use_bmap = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> + num_freed_pages = leak_balloon(vb, oom_pages, use_bmap);
> update_balloon_size(vb);
> *freed += num_freed_pages;
>
> @@ -380,15 +544,19 @@ static void update_balloon_size_func(struct work_struct *work)
> {
> struct virtio_balloon *vb;
> s64 diff;
> + bool use_bmap;
>
> vb = container_of(work, struct virtio_balloon,
> update_balloon_size_work);
> diff = towards_target(vb);
> + use_bmap = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> + if (use_bmap && diff && vb->nr_page_bmap == 1)
> + extend_page_bitmap(vb);

So you allocate it on first use, then keep it around until
device remove? Seems ugly.
Needs comments explaining the motivation for this.
Can't we free it immediately when it becomes unused?

>
> if (diff > 0)
> - diff -= fill_balloon(vb, diff);
> + diff -= fill_balloon(vb, diff, use_bmap);
> else if (diff < 0)
> - diff += leak_balloon(vb, -diff);
> + diff += leak_balloon(vb, -diff, use_bmap);
> update_balloon_size(vb);
>
> if (diff)
> @@ -533,6 +701,17 @@ static int virtballoon_probe(struct virtio_device *vdev)
> spin_lock_init(&vb->stop_update_lock);
> vb->stop_update = false;
> vb->num_pages = 0;
> + vb->bmap_hdr = kzalloc(sizeof(struct balloon_bmap_hdr), GFP_KERNEL);
> + /* Clear the feature bit if memory allocation fails */
> + if (!vb->bmap_hdr)
> + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> + else {
> + vb->page_bitmap[0] = kmalloc(BALLOON_BMAP_SIZE, GFP_KERNEL);
> + if (!vb->page_bitmap[0])
> + __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> + else
> + vb->nr_page_bmap = 1;
> + }
> mutex_init(&vb->balloon_lock);
> init_waitqueue_head(&vb->acked);
> vb->vdev = vdev;
> @@ -583,9 +762,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
>
> static void remove_common(struct virtio_balloon *vb)
> {
> + bool use_bmap;
> +
> + use_bmap = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> /* There might be pages left in the balloon: free them. */
> while (vb->num_pages)
> - leak_balloon(vb, vb->num_pages);
> + leak_balloon(vb, vb->num_pages, use_bmap);
> update_balloon_size(vb);
>
> /* Now we reset the device so we can clean up the queues. */
> @@ -609,6 +791,8 @@ 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->bmap_hdr);
> kfree(vb);
> }
>
> @@ -647,6 +831,7 @@ static int virtballoon_restore(struct virtio_device *vdev)
> VIRTIO_BALLOON_F_MUST_TELL_HOST,
> VIRTIO_BALLOON_F_STATS_VQ,
> VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
> + VIRTIO_BALLOON_F_PAGE_BITMAP,
> };
>
> static struct virtio_driver virtio_balloon_driver = {
> --
> 1.8.3.1

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