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Li, Liang Z

2016-May-24 09:51 UTC

[PATCH RFC kernel] balloon: speed up inflating/deflating process

> On Fri, May 20, 2016 at 05:59:46PM +0800, Liang Li wrote:
> > 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 175ms, it's about 9 times as fast as
before.
> >
> > 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 at intel.com>
> > ---
> >  drivers/virtio/virtio_balloon.c     | 199
> ++++++++++++++++++++++++++++++++++--
> >  include/uapi/linux/virtio_balloon.h |   1 +
> >  mm/page_alloc.c                     |   6 ++
> >  3 files changed, 198 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c
> > b/drivers/virtio/virtio_balloon.c index 7b6d74f..5330b6f 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -45,6 +45,8 @@ 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");
> >
> > +extern unsigned long get_max_pfn(void);
> > +
> >  struct virtio_balloon {
> >  	struct virtio_device *vdev;
> >  	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; @@ -62,6 +64,9
> > @@ struct virtio_balloon {
> >
> >  	/* Number of balloon pages we've told the Host we're not
using. */
> >  	unsigned int num_pages;
> > +	unsigned long *page_bitmap;
> > +	unsigned long start_pfn, end_pfn;
> > +	unsigned long bmap_len;
> >  	/*
> >  	 * The pages we've told the Host we're not using are
enqueued
> >  	 * at vb_dev_info->pages list.
> > @@ -111,15 +116,66 @@ static void balloon_ack(struct virtqueue *vq)
> >  	wake_up(&vb->acked);
> >  }
> >
> > +static int balloon_page_bitmap_init(struct virtio_balloon *vb) {
> > +	unsigned long max_pfn, bmap_bytes;
> > +
> > +	max_pfn = get_max_pfn();
> 
> This is racy. max_pfn could be increased by memory hotplug after you got
it.
> 
> 
> > +	bmap_bytes = ALIGN(max_pfn, BITS_PER_LONG) / BITS_PER_BYTE;
> > +	if (!vb->page_bitmap)
> > +		vb->page_bitmap = kzalloc(bmap_bytes, GFP_KERNEL);
> 
> Likely to fail for a huge busy guest.
> Why not init on device probe?
> this way
> 	- probe will fail, or we can clear the feature bit
> 	- free memory is more likely to be available
> 
Very good suggestion!
> 
> > +	else {
> > +		if (bmap_bytes <= vb->bmap_len)
> > +			memset(vb->page_bitmap, 0, bmap_bytes);
> > +		else {
> > +			kfree(vb->page_bitmap);
> > +			vb->page_bitmap = kzalloc(bmap_bytes,
> GFP_KERNEL);
> > +		}
> > +	}
> > +	if (!vb->page_bitmap) {
> > +		dev_err(&vb->vdev->dev, "%s failure: allocate page
> bitmap\n",
> > +			 __func__);
> > +		return -ENOMEM;
> > +	}
> > +	vb->bmap_len = bmap_bytes;
> > +	vb->start_pfn = max_pfn;
> > +	vb->end_pfn = 0;
> > +
> > +	return 0;
> > +}
> > +
> 
> >  {
> > -	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)) {
> > +		u32 page_shift = PAGE_SHIFT;
> > +		unsigned long start_pfn, end_pfn, flags = 0, bmap_len;
> > +		struct scatterlist sg[5];
> > +
> > +		start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> > +		end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> > +		bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG *
> sizeof(long);
> > +
> > +		sg_init_table(sg, 5);
> > +		sg_set_buf(&sg[0], &flags, sizeof(flags));
> > +		sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn));
> > +		sg_set_buf(&sg[2], &page_shift, sizeof(page_shift));
> > +		sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
> > +		sg_set_buf(&sg[4], vb->page_bitmap +
> > +				 (start_pfn / BITS_PER_LONG), bmap_len);
> 
> This can be pre-initialized, correct?
pre-initialized? I am not quite understand your mean.
> 
> > +		virtqueue_add_outbuf(vq, sg, 5, 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 */ @@
> > -137,7 +193,21 @@ static void set_page_pfns(u32 pfns[], struct page
*page)
> >  		pfns[i] = 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 page
> > +*page) {
> > +	unsigned int i;
> > +	unsigned long *bitmap = vb->page_bitmap;
> > +	unsigned long balloon_pfn = page_to_balloon_pfn(page);
> > +
> > +	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
> > +		set_bit(balloon_pfn + i, bitmap);
> > +	if (balloon_pfn < vb->start_pfn)
> > +		vb->start_pfn = balloon_pfn;
> > +	if (balloon_pfn > vb->end_pfn)
> > +		vb->end_pfn = balloon_pfn;
> > +}
> > +
> > +static unsigned 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;
> > @@ -174,7 +244,104 @@ 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 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 = 0;
> > +
> > +	if (balloon_page_bitmap_init(vb) < 0)
> > +		return num;
> > +
> > +	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;
> > +		}
> > +		set_page_bitmap(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);
> > +	}
> 
> This is grossly inefficient if you only requested a single page.
> And it's also allocating memory very aggressively without ever telling
the host
> what is going on.
If only requested a single page, there is no need  to send the entire page
bitmap,
This RFC patch has already considered about this. But it can works very well if
requesting
several pages  which across a large range.
> > +
> > +	num_allocated_pages = vb->num_pfns;
> > +	/* Did we get any? */
> > +	if (vb->num_pfns != 0)
> > +		tell_host(vb, 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) {
> > +	unsigned long pfn, offset, size;
> > +	struct page *page;
> > +
> > +	size = min(vb->bmap_len * BITS_PER_BYTE, vb->end_pfn);
> > +	for (offset = vb->start_pfn; offset < size;
> > +		 offset = pfn + VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > +		pfn = find_next_bit(vb->page_bitmap, size, offset);
> > +		if (pfn < size) {
> > +			page = balloon_pfn_to_page(pfn);
> > +			if (!virtio_has_feature(vb->vdev,
> > +
> 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> > +				adjust_managed_page_count(page, 1);
> > +			put_page(page);
> > +		}
> > +	}
> > +}
> > +
> > +static unsigned long leak_balloon_bitmap(struct virtio_balloon *vb,
> > +size_t num) {
> > +	unsigned long num_freed_pages = num;
> > +	struct page *page;
> > +	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> > +
> > +	if (balloon_page_bitmap_init(vb) < 0)
> > +		return num_freed_pages;
> > +
> > +	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;
> > +		set_page_bitmap(vb, page);
> > +		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> > +	}
> > +
> > +	num_freed_pages = vb->num_pfns;
> > +
> > +	if (vb->num_pfns != 0)
> > +		tell_host(vb, vb->deflate_vq);
> > +	release_pages_balloon_bitmap(vb);
> > +	mutex_unlock(&vb->balloon_lock);
> > +
> > +	return num_freed_pages;
> > +}
> > +
> > +static void release_pages_balloon_pfns(struct virtio_balloon *vb)
> >  {
> >  	unsigned int i;
> >
> > @@ -188,7 +355,7 @@ static void release_pages_balloon(struct
> virtio_balloon *vb)
> >  	}
> >  }
> >
> > -static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
> > +static unsigned leak_balloon_pfns(struct virtio_balloon *vb, size_t
> > +num)
> >  {
> >  	unsigned num_freed_pages;
> >  	struct page *page;
> > @@ -215,11 +382,23 @@ 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)
> >  {
> > @@ -510,6 +689,8 @@ 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 = NULL;
> > +	vb->bmap_len = 0;
> >  	mutex_init(&vb->balloon_lock);
> >  	init_waitqueue_head(&vb->acked);
> >  	vb->vdev = vdev;
> > @@ -567,6 +748,7 @@ 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);
> >  }
> >
> > @@ -605,6 +787,7 @@ 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 diff --git a/mm/page_alloc.c
> > b/mm/page_alloc.c index c1069ef..74b2fc5 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2139,6 +2139,12 @@ void drain_all_pages(struct zone *zone)
> >  								zone, 1);
> >  }
> >
> > +unsigned long get_max_pfn(void)
> > +{
> > +	return max_pfn;
> > +}
> > +EXPORT_SYMBOL(get_max_pfn);
> > +
> >  #ifdef CONFIG_HIBERNATION
> >
> >  void mark_free_pages(struct zone *zone)
> 
> Suggestion to address all above comments:
> 	1. allocate a bunch of pages and link them up,
> 	   calculating the min and the max pfn.
> 	   if max-min exceeds the allocated bitmap size,
> 	   tell host.
I am not sure if it works well in some cases, e.g. The allocated pages 
are across a wide range and the max-min > limit is very frequently to be
true.
Then, there will be many times of virtio transmission and it's bad for
performance
improvement. Right?

> 	2. limit allocated bitmap size to something reasonable.
> 	   How about 32Kbytes? This is 256kilo bit in the map, which comes
> 	   out to 1Giga bytes of memory in the balloon.
So, even the VM has 1TB of RAM, the page bitmap will take 32MB of memory.
Maybe it's better to use a big page bitmap the save the pages allocated by
balloon,
and split the big page bitmap to 32K bytes unit, then transfer one unit at a
time.


Should we use a page bitmap to replace 'vb->pages' ?

How about rolling back to use PFNs if the count of requested pages is a small
number?

Liang> > --
> > 1.9.1
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
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Li, Liang Z

2016-May-24 09:55 UTC

head link

[PATCH RFC kernel] balloon: speed up inflating/deflating process

> > On Fri, May 20, 2016 at 05:59:46PM +0800, Liang Li wrote:
> > > 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 175ms, it's about 9 times as
fast as before.
> > >
> > > 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 at intel.com>
> > > ---
> > >  drivers/virtio/virtio_balloon.c     | 199
> > ++++++++++++++++++++++++++++++++++--
> > >  include/uapi/linux/virtio_balloon.h |   1 +
> > >  mm/page_alloc.c                     |   6 ++
> > >  3 files changed, 198 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_balloon.c
> > > b/drivers/virtio/virtio_balloon.c index 7b6d74f..5330b6f 100644
> > > --- a/drivers/virtio/virtio_balloon.c
> > > +++ b/drivers/virtio/virtio_balloon.c
> > > @@ -45,6 +45,8 @@ 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");
> > >
> > > +extern unsigned long get_max_pfn(void);
> > > +
> > >  struct virtio_balloon {
> > >  	struct virtio_device *vdev;
> > >  	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; @@ -62,6
> > > +64,9 @@ struct virtio_balloon {
> > >
> > >  	/* Number of balloon pages we've told the Host we're
not using. */
> > >  	unsigned int num_pages;
> > > +	unsigned long *page_bitmap;
> > > +	unsigned long start_pfn, end_pfn;
> > > +	unsigned long bmap_len;
> > >  	/*
> > >  	 * The pages we've told the Host we're not using are
enqueued
> > >  	 * at vb_dev_info->pages list.
> > > @@ -111,15 +116,66 @@ static void balloon_ack(struct virtqueue
*vq)
> > >  	wake_up(&vb->acked);
> > >  }
> > >
> > > +static int balloon_page_bitmap_init(struct virtio_balloon *vb) {
> > > +	unsigned long max_pfn, bmap_bytes;
> > > +
> > > +	max_pfn = get_max_pfn();
> >
> > This is racy. max_pfn could be increased by memory hotplug after you
got it.
> >
> >
> > > +	bmap_bytes = ALIGN(max_pfn, BITS_PER_LONG) / BITS_PER_BYTE;
> > > +	if (!vb->page_bitmap)
> > > +		vb->page_bitmap = kzalloc(bmap_bytes, GFP_KERNEL);
> >
> > Likely to fail for a huge busy guest.
> > Why not init on device probe?
> > this way
> > 	- probe will fail, or we can clear the feature bit
> > 	- free memory is more likely to be available
> >
> 
> Very good suggestion!
> 
> >
> > > +	else {
> > > +		if (bmap_bytes <= vb->bmap_len)
> > > +			memset(vb->page_bitmap, 0, bmap_bytes);
> > > +		else {
> > > +			kfree(vb->page_bitmap);
> > > +			vb->page_bitmap = kzalloc(bmap_bytes,
> > GFP_KERNEL);
> > > +		}
> > > +	}
> > > +	if (!vb->page_bitmap) {
> > > +		dev_err(&vb->vdev->dev, "%s failure: allocate
page
> > bitmap\n",
> > > +			 __func__);
> > > +		return -ENOMEM;
> > > +	}
> > > +	vb->bmap_len = bmap_bytes;
> > > +	vb->start_pfn = max_pfn;
> > > +	vb->end_pfn = 0;
> > > +
> > > +	return 0;
> > > +}
> > > +
> >
> > >  {
> > > -	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)) {
> > > +		u32 page_shift = PAGE_SHIFT;
> > > +		unsigned long start_pfn, end_pfn, flags = 0, bmap_len;
> > > +		struct scatterlist sg[5];
> > > +
> > > +		start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> > > +		end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> > > +		bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG *
> > sizeof(long);
> > > +
> > > +		sg_init_table(sg, 5);
> > > +		sg_set_buf(&sg[0], &flags, sizeof(flags));
> > > +		sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn));
> > > +		sg_set_buf(&sg[2], &page_shift, sizeof(page_shift));
> > > +		sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
> > > +		sg_set_buf(&sg[4], vb->page_bitmap +
> > > +				 (start_pfn / BITS_PER_LONG), bmap_len);
> >
> > This can be pre-initialized, correct?
> 
> pre-initialized? I am not quite understand your mean.
> 
> >
> > > +		virtqueue_add_outbuf(vq, sg, 5, 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 */
@@
> > > -137,7 +193,21 @@ static void set_page_pfns(u32 pfns[], struct
page
> *page)
> > >  		pfns[i] = 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
page
> > > +*page) {
> > > +	unsigned int i;
> > > +	unsigned long *bitmap = vb->page_bitmap;
> > > +	unsigned long balloon_pfn = page_to_balloon_pfn(page);
> > > +
> > > +	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
> > > +		set_bit(balloon_pfn + i, bitmap);
> > > +	if (balloon_pfn < vb->start_pfn)
> > > +		vb->start_pfn = balloon_pfn;
> > > +	if (balloon_pfn > vb->end_pfn)
> > > +		vb->end_pfn = balloon_pfn;
> > > +}
> > > +
> > > +static unsigned 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;
> > > @@ -174,7 +244,104 @@ 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 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 = 0;
> > > +
> > > +	if (balloon_page_bitmap_init(vb) < 0)
> > > +		return num;
> > > +
> > > +	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;
> > > +		}
> > > +		set_page_bitmap(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);
> > > +	}
> >
> > This is grossly inefficient if you only requested a single page.
> > And it's also allocating memory very aggressively without ever
telling
> > the host what is going on.
> 
> If only requested a single page, there is no need  to send the entire page
> bitmap, This RFC patch has already considered about this. But it can works
s/can/can't> very well if requesting several pages  which across a large range.
> 
> > > +
> > > +	num_allocated_pages = vb->num_pfns;
> > > +	/* Did we get any? */
> > > +	if (vb->num_pfns != 0)
> > > +		tell_host(vb, 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) {
> > > +	unsigned long pfn, offset, size;
> > > +	struct page *page;
> > > +
> > > +	size = min(vb->bmap_len * BITS_PER_BYTE, vb->end_pfn);
> > > +	for (offset = vb->start_pfn; offset < size;
> > > +		 offset = pfn + VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > > +		pfn = find_next_bit(vb->page_bitmap, size, offset);
> > > +		if (pfn < size) {
> > > +			page = balloon_pfn_to_page(pfn);
> > > +			if (!virtio_has_feature(vb->vdev,
> > > +
> > 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> > > +				adjust_managed_page_count(page, 1);
> > > +			put_page(page);
> > > +		}
> > > +	}
> > > +}
> > > +
> > > +static unsigned long leak_balloon_bitmap(struct virtio_balloon
*vb,
> > > +size_t num) {
> > > +	unsigned long num_freed_pages = num;
> > > +	struct page *page;
> > > +	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> > > +
> > > +	if (balloon_page_bitmap_init(vb) < 0)
> > > +		return num_freed_pages;
> > > +
> > > +	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;
> > > +		set_page_bitmap(vb, page);
> > > +		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> > > +	}
> > > +
> > > +	num_freed_pages = vb->num_pfns;
> > > +
> > > +	if (vb->num_pfns != 0)
> > > +		tell_host(vb, vb->deflate_vq);
> > > +	release_pages_balloon_bitmap(vb);
> > > +	mutex_unlock(&vb->balloon_lock);
> > > +
> > > +	return num_freed_pages;
> > > +}
> > > +
> > > +static void release_pages_balloon_pfns(struct virtio_balloon
*vb)
> > >  {
> > >  	unsigned int i;
> > >
> > > @@ -188,7 +355,7 @@ static void release_pages_balloon(struct
> > virtio_balloon *vb)
> > >  	}
> > >  }
> > >
> > > -static unsigned leak_balloon(struct virtio_balloon *vb, size_t
num)
> > > +static unsigned leak_balloon_pfns(struct virtio_balloon *vb,
size_t
> > > +num)
> > >  {
> > >  	unsigned num_freed_pages;
> > >  	struct page *page;
> > > @@ -215,11 +382,23 @@ 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)
> > >  {
> > > @@ -510,6 +689,8 @@ 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 = NULL;
> > > +	vb->bmap_len = 0;
> > >  	mutex_init(&vb->balloon_lock);
> > >  	init_waitqueue_head(&vb->acked);
> > >  	vb->vdev = vdev;
> > > @@ -567,6 +748,7 @@ 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);
> > >  }
> > >
> > > @@ -605,6 +787,7 @@ 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 diff --git a/mm/page_alloc.c
> > > b/mm/page_alloc.c index c1069ef..74b2fc5 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2139,6 +2139,12 @@ void drain_all_pages(struct zone *zone)
> > >  								zone, 1);
> > >  }
> > >
> > > +unsigned long get_max_pfn(void)
> > > +{
> > > +	return max_pfn;
> > > +}
> > > +EXPORT_SYMBOL(get_max_pfn);
> > > +
> > >  #ifdef CONFIG_HIBERNATION
> > >
> > >  void mark_free_pages(struct zone *zone)
> >
> > Suggestion to address all above comments:
> > 	1. allocate a bunch of pages and link them up,
> > 	   calculating the min and the max pfn.
> > 	   if max-min exceeds the allocated bitmap size,
> > 	   tell host.
> 
> I am not sure if it works well in some cases, e.g. The allocated pages are
> across a wide range and the max-min > limit is very frequently to be
true.
> Then, there will be many times of virtio transmission and it's bad for
> performance improvement. Right?
> 
> 
> > 	2. limit allocated bitmap size to something reasonable.
> > 	   How about 32Kbytes? This is 256kilo bit in the map, which comes
> > 	   out to 1Giga bytes of memory in the balloon.
> 
> So, even the VM has 1TB of RAM, the page bitmap will take 32MB of memory.
> Maybe it's better to use a big page bitmap the save the pages allocated
by
> balloon,
> and split the big page bitmap to 32K bytes unit, then transfer one unit at
a
> time.
> 
> 
> Should we use a page bitmap to replace 'vb->pages' ?
> 
> How about rolling back to use PFNs if the count of requested pages is a
small
> number?
> 
> Liang
> > > --
> > > 1.9.1
> > --
> > To unsubscribe from this list: send the line "unsubscribe
kvm" in the body
> of
> > a message to majordomo at vger.kernel.org More majordomo info at
> > http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo at vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Michael S. Tsirkin

2016-May-24 10:08 UTC

head link

[PATCH RFC kernel] balloon: speed up inflating/deflating process

On Tue, May 24, 2016 at 09:51:46AM +0000, Li, Liang Z
wrote:> > On Fri, May 20, 2016 at 05:59:46PM +0800, Liang Li wrote:
> > > 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 175ms, it's about 9 times as fast
as before.
> > >
> > > 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 at intel.com>
> > > ---
> > >  drivers/virtio/virtio_balloon.c     | 199
> > ++++++++++++++++++++++++++++++++++--
> > >  include/uapi/linux/virtio_balloon.h |   1 +
> > >  mm/page_alloc.c                     |   6 ++
> > >  3 files changed, 198 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_balloon.c
> > > b/drivers/virtio/virtio_balloon.c index 7b6d74f..5330b6f 100644
> > > --- a/drivers/virtio/virtio_balloon.c
> > > +++ b/drivers/virtio/virtio_balloon.c
> > > @@ -45,6 +45,8 @@ 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");
> > >
> > > +extern unsigned long get_max_pfn(void);
> > > +
> > >  struct virtio_balloon {
> > >  	struct virtio_device *vdev;
> > >  	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; @@ -62,6
+64,9
> > > @@ struct virtio_balloon {
> > >
> > >  	/* Number of balloon pages we've told the Host we're
not using. */
> > >  	unsigned int num_pages;
> > > +	unsigned long *page_bitmap;
> > > +	unsigned long start_pfn, end_pfn;
> > > +	unsigned long bmap_len;
> > >  	/*
> > >  	 * The pages we've told the Host we're not using are
enqueued
> > >  	 * at vb_dev_info->pages list.
> > > @@ -111,15 +116,66 @@ static void balloon_ack(struct virtqueue
*vq)
> > >  	wake_up(&vb->acked);
> > >  }
> > >
> > > +static int balloon_page_bitmap_init(struct virtio_balloon *vb) {
> > > +	unsigned long max_pfn, bmap_bytes;
> > > +
> > > +	max_pfn = get_max_pfn();
> > 
> > This is racy. max_pfn could be increased by memory hotplug after you
got it.
> > 
> > 
> > > +	bmap_bytes = ALIGN(max_pfn, BITS_PER_LONG) / BITS_PER_BYTE;
> > > +	if (!vb->page_bitmap)
> > > +		vb->page_bitmap = kzalloc(bmap_bytes, GFP_KERNEL);
> > 
> > Likely to fail for a huge busy guest.
> > Why not init on device probe?
> > this way
> > 	- probe will fail, or we can clear the feature bit
> > 	- free memory is more likely to be available
> > 
> 
> Very good suggestion!
> 
> > 
> > > +	else {
> > > +		if (bmap_bytes <= vb->bmap_len)
> > > +			memset(vb->page_bitmap, 0, bmap_bytes);
> > > +		else {
> > > +			kfree(vb->page_bitmap);
> > > +			vb->page_bitmap = kzalloc(bmap_bytes,
> > GFP_KERNEL);
> > > +		}
> > > +	}
> > > +	if (!vb->page_bitmap) {
> > > +		dev_err(&vb->vdev->dev, "%s failure: allocate
page
> > bitmap\n",
> > > +			 __func__);
> > > +		return -ENOMEM;
> > > +	}
> > > +	vb->bmap_len = bmap_bytes;
> > > +	vb->start_pfn = max_pfn;
> > > +	vb->end_pfn = 0;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > 
> > >  {
> > > -	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)) {
> > > +		u32 page_shift = PAGE_SHIFT;
> > > +		unsigned long start_pfn, end_pfn, flags = 0, bmap_len;
> > > +		struct scatterlist sg[5];
> > > +
> > > +		start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> > > +		end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> > > +		bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG *
> > sizeof(long);
> > > +
> > > +		sg_init_table(sg, 5);
> > > +		sg_set_buf(&sg[0], &flags, sizeof(flags));
> > > +		sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn));
> > > +		sg_set_buf(&sg[2], &page_shift, sizeof(page_shift));
> > > +		sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
> > > +		sg_set_buf(&sg[4], vb->page_bitmap +
> > > +				 (start_pfn / BITS_PER_LONG), bmap_len);
> > 
> > This can be pre-initialized, correct?
> 
> pre-initialized? I am not quite understand your mean.
I think you can maintain sg as part of device state
and init sg with the bitmap.
> > 
> > > +		virtqueue_add_outbuf(vq, sg, 5, 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 */
@@
> > > -137,7 +193,21 @@ static void set_page_pfns(u32 pfns[], struct
page *page)
> > >  		pfns[i] = 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
page
> > > +*page) {
> > > +	unsigned int i;
> > > +	unsigned long *bitmap = vb->page_bitmap;
> > > +	unsigned long balloon_pfn = page_to_balloon_pfn(page);
> > > +
> > > +	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
> > > +		set_bit(balloon_pfn + i, bitmap);
> > > +	if (balloon_pfn < vb->start_pfn)
> > > +		vb->start_pfn = balloon_pfn;
> > > +	if (balloon_pfn > vb->end_pfn)
> > > +		vb->end_pfn = balloon_pfn;
> > > +}
> > > +
> > > +static unsigned 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;
> > > @@ -174,7 +244,104 @@ 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 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 = 0;
> > > +
> > > +	if (balloon_page_bitmap_init(vb) < 0)
> > > +		return num;
> > > +
> > > +	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;
> > > +		}
> > > +		set_page_bitmap(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);
> > > +	}
> > 
> > This is grossly inefficient if you only requested a single page.
> > And it's also allocating memory very aggressively without ever
telling the host
> > what is going on.
> 
> If only requested a single page, there is no need  to send the entire page
bitmap,
> This RFC patch has already considered about this.
where's that addressed in code?
> But it can works very well if requesting
> several pages  which across a large range.
Some kind of limit on range would make sense though.
It need not cover max pfn.
> > > +
> > > +	num_allocated_pages = vb->num_pfns;
> > > +	/* Did we get any? */
> > > +	if (vb->num_pfns != 0)
> > > +		tell_host(vb, 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) {
> > > +	unsigned long pfn, offset, size;
> > > +	struct page *page;
> > > +
> > > +	size = min(vb->bmap_len * BITS_PER_BYTE, vb->end_pfn);
> > > +	for (offset = vb->start_pfn; offset < size;
> > > +		 offset = pfn + VIRTIO_BALLOON_PAGES_PER_PAGE) {
> > > +		pfn = find_next_bit(vb->page_bitmap, size, offset);
> > > +		if (pfn < size) {
> > > +			page = balloon_pfn_to_page(pfn);
> > > +			if (!virtio_has_feature(vb->vdev,
> > > +
> > 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> > > +				adjust_managed_page_count(page, 1);
> > > +			put_page(page);
> > > +		}
> > > +	}
> > > +}
> > > +
> > > +static unsigned long leak_balloon_bitmap(struct virtio_balloon
*vb,
> > > +size_t num) {
> > > +	unsigned long num_freed_pages = num;
> > > +	struct page *page;
> > > +	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
> > > +
> > > +	if (balloon_page_bitmap_init(vb) < 0)
> > > +		return num_freed_pages;
> > > +
> > > +	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;
> > > +		set_page_bitmap(vb, page);
> > > +		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> > > +	}
> > > +
> > > +	num_freed_pages = vb->num_pfns;
> > > +
> > > +	if (vb->num_pfns != 0)
> > > +		tell_host(vb, vb->deflate_vq);
> > > +	release_pages_balloon_bitmap(vb);
> > > +	mutex_unlock(&vb->balloon_lock);
> > > +
> > > +	return num_freed_pages;
> > > +}
> > > +
> > > +static void release_pages_balloon_pfns(struct virtio_balloon
*vb)
> > >  {
> > >  	unsigned int i;
> > >
> > > @@ -188,7 +355,7 @@ static void release_pages_balloon(struct
> > virtio_balloon *vb)
> > >  	}
> > >  }
> > >
> > > -static unsigned leak_balloon(struct virtio_balloon *vb, size_t
num)
> > > +static unsigned leak_balloon_pfns(struct virtio_balloon *vb,
size_t
> > > +num)
> > >  {
> > >  	unsigned num_freed_pages;
> > >  	struct page *page;
> > > @@ -215,11 +382,23 @@ 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)
> > >  {
> > > @@ -510,6 +689,8 @@ 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 = NULL;
> > > +	vb->bmap_len = 0;
> > >  	mutex_init(&vb->balloon_lock);
> > >  	init_waitqueue_head(&vb->acked);
> > >  	vb->vdev = vdev;
> > > @@ -567,6 +748,7 @@ 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);
> > >  }
> > >
> > > @@ -605,6 +787,7 @@ 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 diff --git a/mm/page_alloc.c
> > > b/mm/page_alloc.c index c1069ef..74b2fc5 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2139,6 +2139,12 @@ void drain_all_pages(struct zone *zone)
> > >  								zone, 1);
> > >  }
> > >
> > > +unsigned long get_max_pfn(void)
> > > +{
> > > +	return max_pfn;
> > > +}
> > > +EXPORT_SYMBOL(get_max_pfn);
> > > +
> > >  #ifdef CONFIG_HIBERNATION
> > >
> > >  void mark_free_pages(struct zone *zone)
> > 
> > Suggestion to address all above comments:
> > 	1. allocate a bunch of pages and link them up,
> > 	   calculating the min and the max pfn.
> > 	   if max-min exceeds the allocated bitmap size,
> > 	   tell host.
> 
> I am not sure if it works well in some cases, e.g. The allocated pages 
> are across a wide range and the max-min > limit is very frequently to be
true.
> Then, there will be many times of virtio transmission and it's bad for
performance
> improvement. Right?
It's a tradeoff for sure. Measure it, see what the overhead is.
> 
> > 	2. limit allocated bitmap size to something reasonable.
> > 	   How about 32Kbytes? This is 256kilo bit in the map, which comes
> > 	   out to 1Giga bytes of memory in the balloon.
> 
> So, even the VM has 1TB of RAM, the page bitmap will take 32MB of memory.
> Maybe it's better to use a big page bitmap the save the pages allocated
by balloon,
> and split the big page bitmap to 32K bytes unit, then transfer one unit at
a time.
How is this different from what I said?
> 
> Should we use a page bitmap to replace 'vb->pages' ?
> 
> How about rolling back to use PFNs if the count of requested pages is a
small number?
> 
> Liang
That's why we have start pfn. you can use that to pass
even a single page without a lot of overhead.
> > > --
> > > 1.9.1
> > --
> > To unsubscribe from this list: send the line "unsubscribe
kvm" in the body of
> > a message to majordomo at vger.kernel.org More majordomo info at
> > http://vger.kernel.org/majordomo-info.html

Li, Liang Z

2016-May-24 10:38 UTC

head link

[PATCH RFC kernel] balloon: speed up inflating/deflating process

> > > >  {
> > > > -	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)) {
> > > > +		u32 page_shift = PAGE_SHIFT;
> > > > +		unsigned long start_pfn, end_pfn, flags = 0, bmap_len;
> > > > +		struct scatterlist sg[5];
> > > > +
> > > > +		start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> > > > +		end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> > > > +		bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG *
> > > sizeof(long);
> > > > +
> > > > +		sg_init_table(sg, 5);
> > > > +		sg_set_buf(&sg[0], &flags, sizeof(flags));
> > > > +		sg_set_buf(&sg[1], &start_pfn,
sizeof(start_pfn));
> > > > +		sg_set_buf(&sg[2], &page_shift,
sizeof(page_shift));
> > > > +		sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
> > > > +		sg_set_buf(&sg[4], vb->page_bitmap +
> > > > +				 (start_pfn / BITS_PER_LONG), bmap_len);
> > >
> > > This can be pre-initialized, correct?
> >
> > pre-initialized? I am not quite understand your mean.
> 
> I think you can maintain sg as part of device state and init sg with the
bitmap.
> 
I got it.
> > > This is grossly inefficient if you only requested a single page.
> > > And it's also allocating memory very aggressively without
ever
> > > telling the host what is going on.
> >
> > If only requested a single page, there is no need  to send the entire
> > page bitmap, This RFC patch has already considered about this.
> 
> where's that addressed in code?
> 
By record the start_pfn and end_pfn.

The start_pfn & end_pfn will be updated in set_page_bitmap()
and will be used in the function tell_host():

---------------------------------------------------------------------------------
+static void set_page_bitmap(struct virtio_balloon *vb, struct page 
+*page) {
+	unsigned int i;
+	unsigned long *bitmap = vb->page_bitmap;
+	unsigned long balloon_pfn = page_to_balloon_pfn(page);
+
+	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
+		set_bit(balloon_pfn + i, bitmap);
+	if (balloon_pfn < vb->start_pfn)
+		vb->start_pfn = balloon_pfn;
+	if (balloon_pfn > vb->end_pfn)
+		vb->end_pfn = balloon_pfn;
+}


+		unsigned long start_pfn, end_pfn, flags = 0, bmap_len;
+		struct scatterlist sg[5];
+
+		start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
+		end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
+		bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG * sizeof(long);
+
+		sg_init_table(sg, 5);
+		sg_set_buf(&sg[0], &flags, sizeof(flags));
+		sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn));
+		sg_set_buf(&sg[2], &page_shift, sizeof(page_shift));
+		sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len));
+		sg_set_buf(&sg[4], vb->page_bitmap +
+				 (start_pfn / BITS_PER_LONG), bmap_len);
+		virtqueue_add_outbuf(vq, sg, 5, vb, GFP_KERNEL);
-------------------------------------------------------------------------------------------> > But it can works very well if requesting several pages  which across a
> > large range.
> 
> Some kind of limit on range would make sense though.
> It need not cover max pfn.
> 
Yes, agree.
> > > Suggestion to address all above comments:
> > > 	1. allocate a bunch of pages and link them up,
> > > 	   calculating the min and the max pfn.
> > > 	   if max-min exceeds the allocated bitmap size,
> > > 	   tell host.
> >
> > I am not sure if it works well in some cases, e.g. The allocated pages
> > are across a wide range and the max-min > limit is very frequently
to be
> true.
> > Then, there will be many times of virtio transmission and it's bad
for
> > performance improvement. Right?
> 
> It's a tradeoff for sure. Measure it, see what the overhead is.
OK, I will try and get back to you.
> 
> >
> > > 	2. limit allocated bitmap size to something reasonable.
> > > 	   How about 32Kbytes? This is 256kilo bit in the map, which
comes
> > > 	   out to 1Giga bytes of memory in the balloon.
> >
> > So, even the VM has 1TB of RAM, the page bitmap will take 32MB of
> memory.
> > Maybe it's better to use a big page bitmap the save the pages
> > allocated by balloon, and split the big page bitmap to 32K bytes unit,
then
> transfer one unit at a time.
> 
> How is this different from what I said?
> 
It's good if it's the same as you said.

Thanks!
Liang
> >
> > Should we use a page bitmap to replace 'vb->pages' ?
> >
> > How about rolling back to use PFNs if the count of requested pages is
a
> small number?
> >
> > Liang
> 
> That's why we have start pfn. you can use that to pass even a single
page
> without a lot of overhead.
> 
> > > > --
> > > > 1.9.1
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe
kvm" in
> > > the body of a message to majordomo at vger.kernel.org More
majordomo
> > > info at http://vger.kernel.org/majordomo-info.html

Li, Liang Z

2016-May-25 08:48 UTC

head link

[PATCH RFC kernel] balloon: speed up inflating/deflating process

> > > Suggestion to address all above comments:
> > > 	1. allocate a bunch of pages and link them up,
> > > 	   calculating the min and the max pfn.
> > > 	   if max-min exceeds the allocated bitmap size,
> > > 	   tell host.
> >
> > I am not sure if it works well in some cases, e.g. The allocated pages
> > are across a wide range and the max-min > limit is very frequently
to be
> true.
> > Then, there will be many times of virtio transmission and it's bad
for
> > performance improvement. Right?
> 
> It's a tradeoff for sure. Measure it, see what the overhead is.
> 
Hi MST,

I have measured the performance when using a 32K page bitmap, and inflate the
balloon to 3GB
of an idle guest with 4GB RAM.

Now: 
total inflating time: 338ms
the count of virtio data transmission:  373
the call count of madvise: 865

before:
total inflating time: 175ms
the count of virtio data transmission: 1
the call count of madvise: 42

Maybe the result will be worse if the guest is not idle, or the guest has more
RAM.
Do you want more data?

Is it worth to do that?

Liang
> >
> > > 	2. limit allocated bitmap size to something reasonable.
> > > 	   How about 32Kbytes? This is 256kilo bit in the map, which
comes
> > > 	   out to 1Giga bytes of memory in the balloon.
> >
> > So, even the VM has 1TB of RAM, the page bitmap will take 32MB of
> memory.
> > Maybe it's better to use a big page bitmap the save the pages
> > allocated by balloon, and split the big page bitmap to 32K bytes unit,
then
> transfer one unit at a time.
> 
> How is this different from what I said?
> 
> >
> > Should we use a page bitmap to replace 'vb->pages' ?
> >
> > How about rolling back to use PFNs if the count of requested pages is
a
> small number?
> >
> > Liang
> 
> That's why we have start pfn. you can use that to pass even a single
page
> without a lot of overhead.
> 
> > > > --
> > > > 1.9.1
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe
kvm" in
> > > the body of a message to majordomo at vger.kernel.org More
majordomo
> > > info at http://vger.kernel.org/majordomo-info.html

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