Re: [Qemu-devel] [PATCH RFC v2 kernel] balloon: speed up inflating/deflating process

[Li, Liang Z]

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Liang


> -----Original Message-----
> From: Li, Liang Z
> Sent: Wednesday, June 01, 2016 10:41 AM
> To: address@hidden
> Cc: address@hidden; address@hidden; Michael S. Tsirkin;
> Paolo Bonzini; Cornelia Huck; Amit Shah
> Subject: RE: [PATCH RFC v2 kernel] balloon: speed up inflating/deflating
> process
> 
> Hi MST,
> 
> About the size of page bitmap, I have test the performance of filling the
> balloon to 15GB with a 16GB RAM VM.
> 
> ===============================
> 32K Byte (cover 1GB of RAM)
> 
> Time spends on inflating: 2031ms
> ---------------------------------------------
> 64K Byte (cover 2GB of RAM)
> 
> Time spends on inflating: 1507ms
> --------------------------------------------
> 512K Byte (cover 16GB of RAM)
> 
> Time spends on inflating: 1237ms
> ================================
> 
> It shows the performance is better if using a larger page bitmap, should we
> use a 64K/ 128KB page bitmap for a better  balance between the
> performance and the memory consumption?
> 
> BTW, about the VIRTIO_BALLOON_F_DEFLATE_ON_OOM feature, I found
> the configurable  'oom_pages'
> will be limited by the ARRAY_SIZE(vb->pfns), which means only 1MB of RAM
> will be recycled each time even the users want more, is that too conservative?
> 
> Liang
> 
> 
> > -----Original Message-----
> > From: Li, Liang Z
> > Sent: Friday, May 27, 2016 6:34 PM
> > To: address@hidden
> > Cc: address@hidden; address@hidden; Li, Liang Z; Michael S.
> > Tsirkin; Paolo Bonzini; Cornelia Huck; Amit Shah
> > Subject: [PATCH RFC v2 kernel] balloon: speed up inflating/deflating
> > process
> >
> > The implementation of the current virtio-balloon is not very
> > efficient, Bellow is test result of time spends on inflating the
> > balloon to 3GB of a 4GB idle
> > guest:
> >
> > a. allocating pages (6.5%, 103ms)
> > b. sending PFNs to host (68.3%, 787ms) c. address translation (6.1%,
> > 96ms) d. madvise (19%, 300ms)
> >
> > It takes about 1577ms for the whole inflating process to complete. The
> > test shows that the bottle neck is the stage b and stage d.
> >
> > If using a bitmap to send the page info instead of the PFNs, we can
> > reduce the overhead spends on stage b quite a lot. Furthermore, it's
> > possible to do the address translation and do the madvise with a bulk
> > of pages, instead of the current page per page way, so 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. And now, inflating the balloon to 3GB of a
> > 4GB idle guest only takes 200ms, it's about 8 times as fast as before.
> >
> > TODO: optimize stage a by allocating/freeing a chunk of pages instead
> > of a single page at a time.
> >
> > v2 change:
> >     1. Use a small page bitmap instead of a large one.
> >     2. Address some of comments of v1.
> >
> > Signed-off-by: Liang Li <address@hidden>
> > Suggested-by: Michael S. Tsirkin <address@hidden>
> > Cc: Michael S. Tsirkin <address@hidden>
> > Cc: Paolo Bonzini <address@hidden>
> > Cc: Cornelia Huck <address@hidden>
> > Cc: Amit Shah <address@hidden>
> > ---
> >  drivers/virtio/virtio_balloon.c     | 207
> > ++++++++++++++++++++++++++++++++++--
> >  include/uapi/linux/virtio_balloon.h |   1 +
> >  2 files changed, 200 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c
> > b/drivers/virtio/virtio_balloon.c index 476c0e3..823b4e4 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -40,11 +40,19 @@
> >  #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256  #define
> > OOM_VBALLOON_DEFAULT_PAGES 256  #define
> > VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
> > +#define VIRTIO_BALLOON_PFNS_LIMIT ((2 * (1ULL << 30)) >>
> PAGE_SHIFT)
> > /*
> > +2GB */
> >
> >  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");
> >
> > +struct balloon_bmap_hdr {
> > +   __virtio32 type;
> > +   __virtio32 page_shift;
> > +   __virtio64 start_pfn;
> > +   __virtio64 bmap_len;
> > +};
> > +
> >  struct virtio_balloon {
> >     struct virtio_device *vdev;
> >     struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; @@ -62,6
> > +70,13 @@ struct virtio_balloon {
> >
> >     /* Number of balloon pages we've told the Host we're not using. */
> >     unsigned int num_pages;
> > +   /* Bitmap and length used to tell the host the pages */
> > +   unsigned long *page_bitmap;
> > +   unsigned long bmap_len;
> > +   /* Used to record the processed pfn range */
> > +   unsigned long min_pfn, max_pfn, start_pfn, end_pfn;
> > +   /* Used for sending page bitmap and header */
> > +   struct scatterlist sg[2];
> >     /*
> >      * The pages we've told the Host we're not using are enqueued
> >      * at vb_dev_info->pages list.
> > @@ -111,15 +126,39 @@ static void balloon_ack(struct virtqueue *vq)
> >     wake_up(&vb->acked);
> >  }
> >
> > +static inline void init_pfn_range(struct virtio_balloon *vb) {
> > +   vb->min_pfn = (1UL << 48);
> > +   vb->max_pfn = 0;
> > +}
> > +
> >  static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)  {
> > -   struct scatterlist sg;
> >     unsigned int len;
> >
> > -   sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
> > +   if (virtio_has_feature(vb->vdev,
> > VIRTIO_BALLOON_F_PAGE_BITMAP)) {
> > +           struct balloon_bmap_hdr hdr;
> > +           unsigned long bmap_len;
> > +
> > +           hdr.type = cpu_to_virtio32(vb->vdev, 0);
> > +           hdr.page_shift = cpu_to_virtio32(vb->vdev, PAGE_SHIFT);
> > +           hdr.start_pfn = cpu_to_virtio64(vb->vdev, vb->start_pfn);
> > +           bmap_len = min(vb->bmap_len,
> > +                         (vb->end_pfn - vb->start_pfn) / BITS_PER_BYTE);
> > +           hdr.bmap_len = cpu_to_virtio64(vb-vdev, bmap_len);
> > +           sg_set_buf(&vb->sg[0], &hdr, sizeof(hdr));
> > +           sg_set_buf(&vb->sg[1], vb->page_bitmap, bmap_len);
> > +           virtqueue_add_outbuf(vq, vb->sg, 2, vb, GFP_KERNEL);
> > +   } else {
> > +           struct scatterlist sg;
> > +
> > +           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.
> > +           */
> > +           virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> > +   }
> >
> > -   /* 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);
> >
> >     /* When host has read buffer, this completes via balloon_ack */ @@
> > -139,7 +178,18 @@ 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 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;
> > +}
> > +
> > +static unsigned int fill_balloon_pfns(struct virtio_balloon *vb,
> > +size_t
> > +num)
> >  {
> >     struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> >     unsigned num_allocated_pages;
> > @@ -176,7 +226,126 @@ static unsigned fill_balloon(struct
> > virtio_balloon *vb, size_t num)
> >     return num_allocated_pages;
> >  }
> >
> > -static void release_pages_balloon(struct virtio_balloon *vb)
> > +static void tell_host_bitmap(struct virtio_balloon *vb,
> > +                    struct list_head *pages, struct virtqueue *vq) {
> > +   unsigned long pfn;
> > +   struct page *page, *next;
> > +   bool find;
> > +
> > +   vb->min_pfn = rounddown(vb->min_pfn, BITS_PER_LONG);
> > +   vb->max_pfn = roundup(vb->max_pfn, BITS_PER_LONG);
> > +   for (pfn = vb->min_pfn; pfn < vb->max_pfn;
> > +                   pfn += VIRTIO_BALLOON_PFNS_LIMIT) {
> > +           vb->start_pfn = pfn;
> > +           vb->end_pfn = pfn;
> > +           memset(vb->page_bitmap, 0, vb->bmap_len);
> > +           find = false;
> > +           list_for_each_entry_safe(page, next, pages, lru) {
> > +                   unsigned long balloon_pfn =
> > page_to_balloon_pfn(page);
> > +
> > +                   if (balloon_pfn < pfn ||
> > +                            balloon_pfn >= pfn +
> > VIRTIO_BALLOON_PFNS_LIMIT)
> > +                           continue;
> > +                   set_bit(balloon_pfn - pfn, vb->page_bitmap);
> > +                   if (balloon_pfn > vb->end_pfn)
> > +                           vb->end_pfn = balloon_pfn;
> > +                   find = true;
> > +           }
> > +           if (find) {
> > +                   vb->end_pfn = roundup(vb->end_pfn,
> > BITS_PER_LONG);
> > +                   tell_host(vb, vq);
> > +           }
> > +   }
> > +}
> > +
> > +static long fill_balloon_bitmap(struct virtio_balloon *vb, size_t
> > +num) {
> > +   struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> > +   long num_allocated_pages;
> > +
> > +   init_pfn_range(vb);
> > +   mutex_lock(&vb->balloon_lock);
> > +   for (vb->num_pfns = 0; vb->num_pfns < num;
> > +           vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > +           struct page *page = balloon_page_enqueue(vb_dev_info);
> > +
> > +           if (!page) {
> > +                   dev_info_ratelimited(&vb->vdev->dev,
> > +                                        "Out of puff! Can't get %u
> > pages\n",
> > +
> > VIRTIO_BALLOON_PAGES_PER_PAGE);
> > +                   /* Sleep for at least 1/5 of a second before retry. */
> > +                   msleep(200);
> > +                   break;
> > +           }
> > +           update_pfn_range(vb, page);
> > +           vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
> > +           if (!virtio_has_feature(vb->vdev,
> > +
> >     VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> > +                   adjust_managed_page_count(page, -1);
> > +   }
> > +
> > +   num_allocated_pages = vb->num_pfns;
> > +   tell_host_bitmap(vb, &vb_dev_info->pages, vb->inflate_vq);
> > +   mutex_unlock(&vb->balloon_lock);
> > +
> > +   return num_allocated_pages;
> > +}
> > +
> > +static long fill_balloon(struct virtio_balloon *vb, size_t num) {
> > +   long num_allocated_pages;
> > +
> > +   if (virtio_has_feature(vb->vdev,
> > VIRTIO_BALLOON_F_PAGE_BITMAP))
> > +           num_allocated_pages = fill_balloon_bitmap(vb, num);
> > +   else
> > +           num_allocated_pages = fill_balloon_pfns(vb, num);
> > +
> > +   return num_allocated_pages;
> > +}
> > +
> > +static void release_pages_balloon_bitmap(struct virtio_balloon *vb,
> > +                            struct list_head *pages)
> > +{
> > +   struct page *page, *next;
> > +
> > +   list_for_each_entry_safe(page, next, pages, lru) {
> > +           if (!virtio_has_feature(vb->vdev,
> > +                   VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> > +                   adjust_managed_page_count(page, 1);
> > +           list_del(&page->lru);
> > +           put_page(page);
> > +   }
> > +}
> > +
> > +static unsigned long leak_balloon_bitmap(struct virtio_balloon *vb,
> > +size_t num) {
> > +   unsigned long num_freed_pages;
> > +   struct page *page;
> > +   struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> > +   LIST_HEAD(pages);
> > +
> > +   init_pfn_range(vb);
> > +   mutex_lock(&vb->balloon_lock);
> > +   for (vb->num_pfns = 0; vb->num_pfns < num;
> > +        vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > +           page = balloon_page_dequeue(vb_dev_info);
> > +           if (!page)
> > +                   break;
> > +           update_pfn_range(vb, page);
> > +           list_add(&page->lru, &pages);
> > +           vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> > +   }
> > +
> > +   num_freed_pages = vb->num_pfns;
> > +   tell_host_bitmap(vb, &pages, vb->deflate_vq);
> > +   release_pages_balloon_bitmap(vb, &pages);
> > +   mutex_unlock(&vb->balloon_lock);
> > +
> > +   return num_freed_pages;
> > +}
> > +
> > +static void release_pages_balloon_pfns(struct virtio_balloon *vb)
> >  {
> >     unsigned int i;
> >     struct page *page;
> > @@ -192,7 +361,7 @@ 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_pfns(struct virtio_balloon *vb,
> > +size_t
> > +num)
> >  {
> >     unsigned num_freed_pages;
> >     struct page *page;
> > @@ -219,11 +388,23 @@ static unsigned leak_balloon(struct
> > virtio_balloon *vb, size_t num)
> >      */
> >     if (vb->num_pfns != 0)
> >             tell_host(vb, vb->deflate_vq);
> > -   release_pages_balloon(vb);
> > +   release_pages_balloon_pfns(vb);
> >     mutex_unlock(&vb->balloon_lock);
> >     return num_freed_pages;
> >  }
> >
> > +static long leak_balloon(struct virtio_balloon *vb, size_t num) {
> > +   long num_freed_pages;
> > +
> > +   if (virtio_has_feature(vb->vdev,
> > VIRTIO_BALLOON_F_PAGE_BITMAP))
> > +           num_freed_pages = leak_balloon_bitmap(vb, num);
> > +   else
> > +           num_freed_pages = leak_balloon_pfns(vb, num);
> > +
> > +   return num_freed_pages;
> > +}
> > +
> >  static inline void update_stat(struct virtio_balloon *vb, int idx,
> >                            u16 tag, u64 val)
> >  {
> > @@ -514,6 +695,14 @@ 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_len = ALIGN(VIRTIO_BALLOON_PFNS_LIMIT,
> > BITS_PER_LONG) /
> > +            BITS_PER_BYTE + 2 * sizeof(unsigned long);
> > +   vb->page_bitmap = kzalloc(vb->bmap_len, GFP_KERNEL);
> > +   if (!vb->page_bitmap) {
> > +           err = -ENOMEM;
> > +           goto out;
> > +   }
> > +   sg_init_table(vb->sg, 2);
> >     mutex_init(&vb->balloon_lock);
> >     init_waitqueue_head(&vb->acked);
> >     vb->vdev = vdev;
> > @@ -571,6 +760,7 @@ static void virtballoon_remove(struct
> > virtio_device
> > *vdev)
> >     cancel_work_sync(&vb->update_balloon_stats_work);
> >
> >     remove_common(vb);
> > +   kfree(vb->page_bitmap);
> >     kfree(vb);
> >  }
> >
> > @@ -609,6 +799,7 @@ 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_BITMAP,
> >  };
> >
> >  static struct virtio_driver virtio_balloon_driver = { diff --git
> > a/include/uapi/linux/virtio_balloon.h
> > b/include/uapi/linux/virtio_balloon.h
> > index 343d7dd..f78fa47 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_BITMAP       3 /* Send page info
> with
> > bitmap */
> >
> >  /* Size of a PFN in the balloon interface. */  #define
> > VIRTIO_BALLOON_PFN_SHIFT 12
> > --
> > 1.9.1