Virtualization - Jul 2016 - [PATCH v2 repost 4/7] virtio-balloon: speed up inflate/deflate process

This patchset is for kernel and contains two parts of change to the
virtio-balloon. 

One is the change for speeding up the inflating & deflating process,
the main idea of this optimization is to use bitmap to send the page
information to host instead of the PFNs, to reduce the overhead of
virtio data transmission, address translation and madvise(). This can
help to improve the performance by about 85%.

Another change is for speeding up live migration. By skipping process
guest's free pages in the first round of data copy, to reduce needless
data processing, this can help to save quite a lot of CPU cycles and
network bandwidth. We put guest's free page information in bitmap and
send it to host with the virt queue of virtio-balloon. For an idle 8GB
guest, this can help to shorten the total live migration time from 2Sec
to about 500ms in the 10Gbps network environment.  


Changes from v1 to v2:
    * Abandon the patch for dropping page cache.
    * Put some structures to uapi head file.
    * Use a new way to determine the page bitmap size.
    * Use a unified way to send the free page information with the bitmap 
    * Address the issues referred in MST's comments

Liang Li (7):
  virtio-balloon: rework deflate to add page to a list
  virtio-balloon: define new feature bit and page bitmap head
  mm: add a function to get the max pfn
  virtio-balloon: speed up inflate/deflate process
  virtio-balloon: define feature bit and head for misc virt queue
  mm: add the related functions to get free page info
  virtio-balloon: tell host vm's free page info

 drivers/virtio/virtio_balloon.c     | 306 +++++++++++++++++++++++++++++++-----
 include/uapi/linux/virtio_balloon.h |  41 +++++
 mm/page_alloc.c                     |  52 ++++++
 3 files changed, 359 insertions(+), 40 deletions(-)

-- 
1.9.1

will allow faster notifications using a bitmap down the road.
balloon_pfn_to_page() can be removed because it's useless.

Signed-off-by: Liang Li <liang.z.li at intel.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 drivers/virtio/virtio_balloon.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 476c0e3..8d649a2 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -98,12 +98,6 @@ static u32 page_to_balloon_pfn(struct page *page)
 	return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 }
 
-static struct page *balloon_pfn_to_page(u32 pfn)
-{
-	BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
-	return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
-}
-
 static void balloon_ack(struct virtqueue *vq)
 {
 	struct virtio_balloon *vb = vq->vdev->priv;
@@ -176,18 +170,16 @@ 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 release_pages_balloon(struct virtio_balloon *vb,
+				 struct list_head *pages)
 {
-	unsigned int i;
-	struct page *page;
+	struct page *page, *next;
 
-	/* Find pfns pointing at start of each page, get pages and free them. */
-	for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
-		page = balloon_pfn_to_page(virtio32_to_cpu(vb->vdev,
-							   vb->pfns[i]));
+	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); /* balloon reference */
 	}
 }
@@ -197,6 +189,7 @@ static unsigned leak_balloon(struct virtio_balloon *vb,
size_t num)
 	unsigned 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));
@@ -208,6 +201,7 @@ static unsigned leak_balloon(struct virtio_balloon *vb,
size_t num)
 		if (!page)
 			break;
 		set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
+		list_add(&page->lru, &pages);
 		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 	}
 
@@ -219,7 +213,7 @@ 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(vb, &pages);
 	mutex_unlock(&vb->balloon_lock);
 	return num_freed_pages;
 }
-- 
1.9.1

Add a new feature which supports sending the page information with
a bitmap. The current implementation uses PFNs array, which is not
very efficient. Using bitmap can improve the performance of
inflating/deflating significantly

The page bitmap header will used to tell the host some information
about the page bitmap. e.g. the page size, page bitmap length and
start pfn.

Signed-off-by: Liang Li <liang.z.li at intel.com>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 include/uapi/linux/virtio_balloon.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/uapi/linux/virtio_balloon.h
b/include/uapi/linux/virtio_balloon.h
index 343d7dd..d3b182a 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
@@ -82,4 +83,22 @@ struct virtio_balloon_stat {
 	__virtio64 val;
 } __attribute__((packed));
 
+/* Page bitmap header structure */
+struct balloon_bmap_hdr {
+	/* Used to distinguish different request */
+	__virtio16 cmd;
+	/* Shift width of page in the bitmap */
+	__virtio16 page_shift;
+	/* flag used to identify different status */
+	__virtio16 flag;
+	/* Reserved */
+	__virtio16 reserved;
+	/* ID of the request */
+	__virtio64 req_id;
+	/* The pfn of 0 bit in the bitmap */
+	__virtio64 start_pfn;
+	/* The length of the bitmap, in bytes */
+	__virtio64 bmap_len;
+};
+
 #endif /* _LINUX_VIRTIO_BALLOON_H */
-- 
1.9.1

Expose the function to get the max pfn, so it can be used in the
virtio-balloon device driver.

Signed-off-by: Liang Li <liang.z.li at intel.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 mm/page_alloc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8b3e134..7da61ad 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4517,6 +4517,12 @@ void show_free_areas(unsigned int filter)
 	show_swap_cache_info();
 }
 
+unsigned long get_max_pfn(void)
+{
+	return max_pfn;
+}
+EXPORT_SYMBOL(get_max_pfn);
+
 static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
 {
 	zoneref->zone = zone;
-- 
1.9.1

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 at intel.com>
Suggested-by: Michael S. Tsirkin <mst at redhat.com>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 drivers/virtio/virtio_balloon.c | 184 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 162 insertions(+), 22 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 8d649a2..2d18ff6 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -41,10 +41,28 @@
 #define OOM_VBALLOON_DEFAULT_PAGES 256
 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
 
+/*
+ * VIRTIO_BALLOON_PFNS_LIMIT is used to limit the size of page bitmap
+ * to prevent a very large page bitmap, there are two reasons for this:
+ * 1) to save memory.
+ * 2) allocate a large bitmap may fail.
+ *
+ * The actual limit of pfn is determined by:
+ * pfn_limit = min(max_pfn, VIRTIO_BALLOON_PFNS_LIMIT);
+ *
+ * If system has more pages than VIRTIO_BALLOON_PFNS_LIMIT, we will scan
+ * the page list and send the PFNs with several times. To reduce the
+ * overhead of scanning the page list. VIRTIO_BALLOON_PFNS_LIMIT should
+ * be set with a value which can cover most cases.
+ */
+#define VIRTIO_BALLOON_PFNS_LIMIT ((32 * (1ULL << 30)) >>
PAGE_SHIFT) /* 32GB */
+
 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 +80,15 @@ 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 length used to tell the host the pages */
+	unsigned long *page_bitmap;
+	unsigned long bmap_len;
+	/* Pfn limit */
+	unsigned long pfn_limit;
+	/* 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.
@@ -105,12 +132,45 @@ 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;
+}
+
 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 = vb->bmap_hdr;
+		unsigned long bmap_len;
+
+		/* cmd and req_id are not used here, set them to 0 */
+		hdr->cmd = cpu_to_virtio16(vb->vdev, 0);
+		hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
+		hdr->reserved = cpu_to_virtio16(vb->vdev, 0);
+		hdr->req_id = cpu_to_virtio64(vb->vdev, 0);
+		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_init_one(&sg, hdr,
+			 sizeof(struct balloon_bmap_hdr) + bmap_len);
+	} 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. */
 	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
@@ -118,7 +178,6 @@ 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 set_page_pfns(struct virtio_balloon *vb,
@@ -133,13 +192,53 @@ static void set_page_pfns(struct virtio_balloon *vb,
 					  page_to_balloon_pfn(page) + i);
 }
 
-static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
+static void set_page_bitmap(struct virtio_balloon *vb,
+			 struct list_head *pages, struct virtqueue *vq)
+{
+	unsigned long pfn;
+	struct page *page;
+	bool found;
+
+	vb->min_pfn = rounddown(vb->min_pfn, BITS_PER_LONG);
+	vb->max_pfn = roundup(vb->max_pfn, BITS_PER_LONG);
+	for (pfn = vb->min_pfn; pfn < vb->max_pfn;
+			pfn += vb->pfn_limit) {
+		vb->start_pfn = pfn + vb->pfn_limit;
+		vb->end_pfn = pfn;
+		memset(vb->page_bitmap, 0, vb->bmap_len);
+		found = false;
+		list_for_each_entry(page, pages, lru) {
+			unsigned long balloon_pfn = page_to_balloon_pfn(page);
+
+			if (balloon_pfn < pfn ||
+				 balloon_pfn >= pfn + vb->pfn_limit)
+				continue;
+			set_bit(balloon_pfn - pfn, vb->page_bitmap);
+			if (balloon_pfn > vb->end_pfn)
+				vb->end_pfn = balloon_pfn;
+			if (balloon_pfn < vb->start_pfn)
+				vb->start_pfn = balloon_pfn;
+			found = true;
+		}
+		if (found) {
+			vb->start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
+			vb->end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
+			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;
@@ -154,7 +253,10 @@ 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))
@@ -163,8 +265,13 @@ 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;
@@ -184,15 +291,19 @@ 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)
 {
-	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);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
@@ -200,7 +311,10 @@ 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;
 	}
@@ -211,9 +325,14 @@ 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);
-	release_pages_balloon(vb, &pages);
+	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);
+	}
 	mutex_unlock(&vb->balloon_lock);
 	return num_freed_pages;
 }
@@ -347,13 +466,15 @@ 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;
 
@@ -373,15 +494,17 @@ 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);
+	use_bmap = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
 	diff = towards_target(vb);
 
 	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)
@@ -489,7 +612,7 @@ static int virtballoon_migratepage(struct balloon_dev_info
*vb_dev_info,
 static int virtballoon_probe(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb;
-	int err;
+	int err, hdr_len;
 
 	if (!vdev->config->get) {
 		dev_err(&vdev->dev, "%s failure: config access disabled\n",
@@ -508,6 +631,18 @@ static int virtballoon_probe(struct virtio_device *vdev)
 	spin_lock_init(&vb->stop_update_lock);
 	vb->stop_update = false;
 	vb->num_pages = 0;
+	vb->pfn_limit = VIRTIO_BALLOON_PFNS_LIMIT;
+	vb->pfn_limit = min(vb->pfn_limit, get_max_pfn());
+	vb->bmap_len = ALIGN(vb->pfn_limit, BITS_PER_LONG) /
+		 BITS_PER_BYTE + 2 * sizeof(unsigned long);
+	hdr_len = sizeof(struct balloon_bmap_hdr);
+	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, 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 = vb->bmap_hdr + hdr_len;
 	mutex_init(&vb->balloon_lock);
 	init_waitqueue_head(&vb->acked);
 	vb->vdev = vdev;
@@ -541,9 +676,12 @@ out:
 
 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. */
@@ -565,6 +703,7 @@ 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);
 }
 
@@ -603,6 +742,7 @@ 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 = {
-- 
1.9.1

Define a new feature bit which supports a new virtual queue. This
new virtual qeuque is for information exchange between hypervisor
and guest. The VMM hypervisor can make use of this virtual queue
to request the guest do some operations, e.g. drop page cache,
synchronize file system, etc. And the VMM hypervisor can get some
of guest's runtime information through this virtual queue, e.g. the
guest's free page information, which can be used for live migration
optimization.

Signed-off-by: Liang Li <liang.z.li at intel.com>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 include/uapi/linux/virtio_balloon.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/uapi/linux/virtio_balloon.h
b/include/uapi/linux/virtio_balloon.h
index d3b182a..be4880f 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -35,6 +35,7 @@
 #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 */
+#define VIRTIO_BALLOON_F_MISC_VQ	4 /* Misc info virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
@@ -101,4 +102,25 @@ struct balloon_bmap_hdr {
 	__virtio64 bmap_len;
 };
 
+enum balloon_req_id {
+	/* Get free pages information */
+	BALLOON_GET_FREE_PAGES,
+};
+
+enum balloon_flag {
+	/* Have more data for a request */
+	BALLOON_FLAG_CONT,
+	/* No more data for a request */
+	BALLOON_FLAG_DONE,
+};
+
+struct balloon_req_hdr {
+	/* Used to distinguish different request */
+	__virtio16 cmd;
+	/* Reserved */
+	__virtio16 reserved[3];
+	/* Request parameter */
+	__virtio64 param;
+};
+
 #endif /* _LINUX_VIRTIO_BALLOON_H */
-- 
1.9.1

Save the free page info into a page bitmap, will be used in virtio
balloon device driver.

Signed-off-by: Liang Li <liang.z.li at intel.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7da61ad..3ad8b10 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4523,6 +4523,52 @@ unsigned long get_max_pfn(void)
 }
 EXPORT_SYMBOL(get_max_pfn);
 
+static void mark_free_pages_bitmap(struct zone *zone, unsigned long start_pfn,
+	unsigned long end_pfn, unsigned long *bitmap, unsigned long len)
+{
+	unsigned long pfn, flags, page_num;
+	unsigned int order, t;
+	struct list_head *curr;
+
+	if (zone_is_empty(zone))
+		return;
+	end_pfn = min(start_pfn + len, end_pfn);
+	spin_lock_irqsave(&zone->lock, flags);
+
+	for_each_migratetype_order(order, t) {
+		list_for_each(curr, &zone->free_area[order].free_list[t]) {
+			pfn = page_to_pfn(list_entry(curr, struct page, lru));
+			if (pfn >= start_pfn && pfn <= end_pfn) {
+				page_num = 1UL << order;
+				if (pfn + page_num > end_pfn)
+					page_num = end_pfn - pfn;
+				bitmap_set(bitmap, pfn - start_pfn, page_num);
+			}
+		}
+	}
+
+	spin_unlock_irqrestore(&zone->lock, flags);
+}
+
+int get_free_pages(unsigned long start_pfn, unsigned long end_pfn,
+		unsigned long *bitmap, unsigned long len)
+{
+	struct zone *zone;
+	int ret = 0;
+
+	if (bitmap == NULL || start_pfn > end_pfn || start_pfn >= max_pfn)
+		return 0;
+	if (end_pfn < max_pfn)
+		ret = 1;
+	if (end_pfn >= max_pfn)
+		ret = 0;
+
+	for_each_populated_zone(zone)
+		mark_free_pages_bitmap(zone, start_pfn, end_pfn, bitmap, len);
+	return ret;
+}
+EXPORT_SYMBOL(get_free_pages);
+
 static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
 {
 	zoneref->zone = zone;
-- 
1.9.1

Support the request for vm's free page information, response with
a page bitmap. QEMU can make use of this free page bitmap to speed
up live migration process by skipping process the free pages.

Signed-off-by: Liang Li <liang.z.li at intel.com>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Vlastimil Babka <vbabka at suse.cz>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
Cc: Amit Shah <amit.shah at redhat.com>
---
 drivers/virtio/virtio_balloon.c | 104 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 98 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 2d18ff6..5ca4ad3 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -62,10 +62,13 @@ 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);
+extern int get_free_pages(unsigned long start_pfn, unsigned long end_pfn,
+		unsigned long *bitmap, unsigned long len);
+
 
 struct virtio_balloon {
 	struct virtio_device *vdev;
-	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
+	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *misc_vq;
 
 	/* The balloon servicing is delegated to a freezable workqueue. */
 	struct work_struct update_balloon_stats_work;
@@ -89,6 +92,8 @@ struct virtio_balloon {
 	unsigned long pfn_limit;
 	/* Used to record the processed pfn range */
 	unsigned long min_pfn, max_pfn, start_pfn, end_pfn;
+	/* Request header */
+	struct balloon_req_hdr req_hdr;
 	/*
 	 * The pages we've told the Host we're not using are enqueued
 	 * at vb_dev_info->pages list.
@@ -373,6 +378,49 @@ static void update_balloon_stats(struct virtio_balloon *vb)
 				pages_to_bytes(available));
 }
 
+static void update_free_pages_stats(struct virtio_balloon *vb,
+				unsigned long req_id)
+{
+	struct scatterlist sg_in, sg_out;
+	unsigned long pfn = 0, bmap_len, max_pfn;
+	struct virtqueue *vq = vb->misc_vq;
+	struct balloon_bmap_hdr *hdr = vb->bmap_hdr;
+	int ret = 1;
+
+	max_pfn = get_max_pfn();
+	mutex_lock(&vb->balloon_lock);
+	while (pfn < max_pfn) {
+		memset(vb->page_bitmap, 0, vb->bmap_len);
+		ret = get_free_pages(pfn, pfn + vb->pfn_limit,
+			vb->page_bitmap, vb->bmap_len * BITS_PER_BYTE);
+		hdr->cmd = cpu_to_virtio16(vb->vdev, BALLOON_GET_FREE_PAGES);
+		hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
+		hdr->req_id = cpu_to_virtio64(vb->vdev, req_id);
+		hdr->start_pfn = cpu_to_virtio64(vb->vdev, pfn);
+		bmap_len = vb->pfn_limit / BITS_PER_BYTE;
+		if (!ret) {
+			hdr->flag = cpu_to_virtio16(vb->vdev,
+							BALLOON_FLAG_DONE);
+			if (pfn + vb->pfn_limit > max_pfn)
+				bmap_len = (max_pfn - pfn) / BITS_PER_BYTE;
+		} else
+			hdr->flag = cpu_to_virtio16(vb->vdev,
+							BALLOON_FLAG_CONT);
+		hdr->bmap_len = cpu_to_virtio64(vb->vdev, bmap_len);
+		sg_init_one(&sg_out, hdr,
+			 sizeof(struct balloon_bmap_hdr) + bmap_len);
+
+		virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL);
+		virtqueue_kick(vq);
+		pfn += vb->pfn_limit;
+	}
+
+	sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
+	virtqueue_add_inbuf(vq, &sg_in, 1, &vb->req_hdr, GFP_KERNEL);
+	virtqueue_kick(vq);
+	mutex_unlock(&vb->balloon_lock);
+}
+
 /*
  * While most virtqueues communicate guest-initiated requests to the
hypervisor,
  * the stats queue operates in reverse.  The driver initializes the virtqueue
@@ -511,18 +559,49 @@ static void update_balloon_size_func(struct work_struct
*work)
 		queue_work(system_freezable_wq, work);
 }
 
+static void misc_handle_rq(struct virtio_balloon *vb)
+{
+	struct balloon_req_hdr *ptr_hdr;
+	unsigned int len;
+
+	ptr_hdr = virtqueue_get_buf(vb->misc_vq, &len);
+	if (!ptr_hdr || len != sizeof(vb->req_hdr))
+		return;
+
+	switch (ptr_hdr->cmd) {
+	case BALLOON_GET_FREE_PAGES:
+		update_free_pages_stats(vb, ptr_hdr->param);
+		break;
+	default:
+		break;
+	}
+}
+
+static void misc_request(struct virtqueue *vq)
+{
+	struct virtio_balloon *vb = vq->vdev->priv;
+
+	misc_handle_rq(vb);
+}
+
 static int init_vqs(struct virtio_balloon *vb)
 {
-	struct virtqueue *vqs[3];
-	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
-	static const char * const names[] = { "inflate",
"deflate", "stats" };
+	struct virtqueue *vqs[4];
+	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack,
+					 stats_request, misc_request };
+	static const char * const names[] = { "inflate",
"deflate", "stats",
+						 "misc" };
 	int err, nvqs;
 
 	/*
 	 * We expect two virtqueues: inflate and deflate, and
 	 * optionally stat.
 	 */
-	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ))
+		nvqs = 4;
+	else
+		nvqs = virtio_has_feature(vb->vdev,
+					  VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 	err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks,
names);
 	if (err)
 		return err;
@@ -543,6 +622,16 @@ static int init_vqs(struct virtio_balloon *vb)
 			BUG();
 		virtqueue_kick(vb->stats_vq);
 	}
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ)) {
+		struct scatterlist sg_in;
+
+		vb->misc_vq = vqs[3];
+		sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
+		if (virtqueue_add_inbuf(vb->misc_vq, &sg_in, 1,
+		    &vb->req_hdr, GFP_KERNEL) < 0)
+			BUG();
+		virtqueue_kick(vb->misc_vq);
+	}
 	return 0;
 }
 
@@ -639,8 +728,10 @@ static int virtballoon_probe(struct virtio_device *vdev)
 	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
 
 	/* Clear the feature bit if memory allocation fails */
-	if (!vb->bmap_hdr)
+	if (!vb->bmap_hdr) {
 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_MISC_VQ);
+	}
 	else
 		vb->page_bitmap = vb->bmap_hdr + hdr_len;
 	mutex_init(&vb->balloon_lock);
@@ -743,6 +834,7 @@ static unsigned int features[] = {
 	VIRTIO_BALLOON_F_STATS_VQ,
 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
 	VIRTIO_BALLOON_F_PAGE_BITMAP,
+	VIRTIO_BALLOON_F_MISC_VQ,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
-- 
1.9.1

On 07/26/2016 06:23 PM, Liang Li wrote:
> +	vb->pfn_limit = VIRTIO_BALLOON_PFNS_LIMIT;
> +	vb->pfn_limit = min(vb->pfn_limit, get_max_pfn());
> +	vb->bmap_len = ALIGN(vb->pfn_limit, BITS_PER_LONG) /
> +		 BITS_PER_BYTE + 2 * sizeof(unsigned long);
> +	hdr_len = sizeof(struct balloon_bmap_hdr);
> +	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
This ends up doing a 1MB kmalloc() right?  That seems a _bit_ big.  How
big was the pfn buffer before?

On 07/26/2016 06:23 PM, Liang Li wrote:
> +	for_each_migratetype_order(order, t) {
> +		list_for_each(curr, &zone->free_area[order].free_list[t]) {
> +			pfn = page_to_pfn(list_entry(curr, struct page, lru));
> +			if (pfn >= start_pfn && pfn <= end_pfn) {
> +				page_num = 1UL << order;
> +				if (pfn + page_num > end_pfn)
> +					page_num = end_pfn - pfn;
> +				bitmap_set(bitmap, pfn - start_pfn, page_num);
> +			}
> +		}
> +	}
Nit:  The 'page_num' nomenclature really confused me here.  It is the
number of bits being set in the bitmap.  Seems like calling it nr_pages
or num_pages would be more appropriate.

Isn't this bitmap out of date by the time it's send up to the
hypervisor?  Is there something that makes the inaccuracy OK here?

On Wed, Jul 27, 2016 at 09:23:33AM +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 at intel.com>
> Suggested-by: Michael S. Tsirkin <mst at redhat.com>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Amit Shah <amit.shah at redhat.com>
> ---
>  drivers/virtio/virtio_balloon.c | 184
+++++++++++++++++++++++++++++++++++-----
>  1 file changed, 162 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> index 8d649a2..2d18ff6 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -41,10 +41,28 @@
>  #define OOM_VBALLOON_DEFAULT_PAGES 256
>  #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>  
> +/*
> + * VIRTIO_BALLOON_PFNS_LIMIT is used to limit the size of page bitmap
> + * to prevent a very large page bitmap, there are two reasons for this:
> + * 1) to save memory.
> + * 2) allocate a large bitmap may fail.
> + *
> + * The actual limit of pfn is determined by:
> + * pfn_limit = min(max_pfn, VIRTIO_BALLOON_PFNS_LIMIT);
> + *
> + * If system has more pages than VIRTIO_BALLOON_PFNS_LIMIT, we will scan
> + * the page list and send the PFNs with several times. To reduce the
> + * overhead of scanning the page list. VIRTIO_BALLOON_PFNS_LIMIT should
> + * be set with a value which can cover most cases.
So what if it covers 1/32 of the memory? We'll do 32 exits and not 1,
still not a big deal for a big guest.
> + */
> +#define VIRTIO_BALLOON_PFNS_LIMIT ((32 * (1ULL << 30)) >>
PAGE_SHIFT) /* 32GB */
I already said this with a smaller limit.

	2<< 30  is 2G but that is not a useful comment.
	pls explain what is the reason for this selection.

Still applies here.

> +
>  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 +80,15 @@ 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 length used to tell the host the pages */
> +	unsigned long *page_bitmap;
> +	unsigned long bmap_len;
> +	/* Pfn limit */
> +	unsigned long pfn_limit;
> +	/* 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.
> @@ -105,12 +132,45 @@ 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;
> +}
> +
>  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 = vb->bmap_hdr;
> +		unsigned long bmap_len;
> +
> +		/* cmd and req_id are not used here, set them to 0 */
> +		hdr->cmd = cpu_to_virtio16(vb->vdev, 0);
> +		hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
> +		hdr->reserved = cpu_to_virtio16(vb->vdev, 0);
> +		hdr->req_id = cpu_to_virtio64(vb->vdev, 0);
no need to swap 0, just fill it in. in fact you allocated all 0s
so no need to touch these fields at all.
> +		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_init_one(&sg, hdr,
> +			 sizeof(struct balloon_bmap_hdr) + bmap_len);
> +	} 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. */
>  	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> @@ -118,7 +178,6 @@ 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 set_page_pfns(struct virtio_balloon *vb,
> @@ -133,13 +192,53 @@ static void set_page_pfns(struct virtio_balloon *vb,
>  					  page_to_balloon_pfn(page) + i);
>  }
>  
> -static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> +static void set_page_bitmap(struct virtio_balloon *vb,
> +			 struct list_head *pages, struct virtqueue *vq)
> +{
> +	unsigned long pfn;
> +	struct page *page;
> +	bool found;
> +
> +	vb->min_pfn = rounddown(vb->min_pfn, BITS_PER_LONG);
> +	vb->max_pfn = roundup(vb->max_pfn, BITS_PER_LONG);
> +	for (pfn = vb->min_pfn; pfn < vb->max_pfn;
> +			pfn += vb->pfn_limit) {
> +		vb->start_pfn = pfn + vb->pfn_limit;
> +		vb->end_pfn = pfn;
> +		memset(vb->page_bitmap, 0, vb->bmap_len);
> +		found = false;
> +		list_for_each_entry(page, pages, lru) {
> +			unsigned long balloon_pfn = page_to_balloon_pfn(page);
> +
> +			if (balloon_pfn < pfn ||
> +				 balloon_pfn >= pfn + vb->pfn_limit)
> +				continue;
> +			set_bit(balloon_pfn - pfn, vb->page_bitmap);
> +			if (balloon_pfn > vb->end_pfn)
> +				vb->end_pfn = balloon_pfn;
> +			if (balloon_pfn < vb->start_pfn)
> +				vb->start_pfn = balloon_pfn;
> +			found = true;
> +		}
> +		if (found) {
> +			vb->start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> +			vb->end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> +			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;
> @@ -154,7 +253,10 @@ 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))
> @@ -163,8 +265,13 @@ 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;
> @@ -184,15 +291,19 @@ 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)
>  {
> -	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);
>  	for (vb->num_pfns = 0; vb->num_pfns < num;
> @@ -200,7 +311,10 @@ 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;
>  	}
> @@ -211,9 +325,14 @@ 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);
> -	release_pages_balloon(vb, &pages);
> +	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);
> +	}
>  	mutex_unlock(&vb->balloon_lock);
>  	return num_freed_pages;
>  }
> @@ -347,13 +466,15 @@ 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;
>  
> @@ -373,15 +494,17 @@ 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);
> +	use_bmap = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
>  	diff = towards_target(vb);
>  
>  	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)
> @@ -489,7 +612,7 @@ static int virtballoon_migratepage(struct
balloon_dev_info *vb_dev_info,
>  static int virtballoon_probe(struct virtio_device *vdev)
>  {
>  	struct virtio_balloon *vb;
> -	int err;
> +	int err, hdr_len;
>  
>  	if (!vdev->config->get) {
>  		dev_err(&vdev->dev, "%s failure: config access
disabled\n",
> @@ -508,6 +631,18 @@ static int virtballoon_probe(struct virtio_device
*vdev)
>  	spin_lock_init(&vb->stop_update_lock);
>  	vb->stop_update = false;
>  	vb->num_pages = 0;
> +	vb->pfn_limit = VIRTIO_BALLOON_PFNS_LIMIT;
> +	vb->pfn_limit = min(vb->pfn_limit, get_max_pfn());
> +	vb->bmap_len = ALIGN(vb->pfn_limit, BITS_PER_LONG) /
> +		 BITS_PER_BYTE + 2 * sizeof(unsigned long);
What are these 2 longs in aid of?
> +	hdr_len = sizeof(struct balloon_bmap_hdr);
> +	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
So it can go up to 1MByte but adding header size etc you need a higher
order allocation. This is a waste, there is no need to have a power of
two allocation. Start from the other side. Say "I want to allocate
32KBytes for the bitmap". Subtract the header and you get bitmap size.
Calculate the pfn limit from there.

> +
> +	/* 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 = vb->bmap_hdr + hdr_len;
>  	mutex_init(&vb->balloon_lock);
>  	init_waitqueue_head(&vb->acked);
>  	vb->vdev = vdev;
> @@ -541,9 +676,12 @@ out:
>  
>  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. */
> @@ -565,6 +703,7 @@ 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);
>  }
>  
> @@ -603,6 +742,7 @@ 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 = {
> -- 
> 1.9.1

On Wed, Jul 27, 2016 at 09:23:36AM +0800, Liang Li
wrote:
> Support the request for vm's free page information, response with
> a page bitmap. QEMU can make use of this free page bitmap to speed
> up live migration process by skipping process the free pages.
> 
> Signed-off-by: Liang Li <liang.z.li at intel.com>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Amit Shah <amit.shah at redhat.com>
> ---
>  drivers/virtio/virtio_balloon.c | 104
+++++++++++++++++++++++++++++++++++++---
>  1 file changed, 98 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> index 2d18ff6..5ca4ad3 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -62,10 +62,13 @@ 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);
> +extern int get_free_pages(unsigned long start_pfn, unsigned long end_pfn,
> +		unsigned long *bitmap, unsigned long len);
> +
>  
>  struct virtio_balloon {
>  	struct virtio_device *vdev;
> -	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> +	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *misc_vq;
>  
>  	/* The balloon servicing is delegated to a freezable workqueue. */
>  	struct work_struct update_balloon_stats_work;
> @@ -89,6 +92,8 @@ struct virtio_balloon {
>  	unsigned long pfn_limit;
>  	/* Used to record the processed pfn range */
>  	unsigned long min_pfn, max_pfn, start_pfn, end_pfn;
> +	/* Request header */
> +	struct balloon_req_hdr req_hdr;
>  	/*
>  	 * The pages we've told the Host we're not using are enqueued
>  	 * at vb_dev_info->pages list.
> @@ -373,6 +378,49 @@ static void update_balloon_stats(struct virtio_balloon
*vb)
>  				pages_to_bytes(available));
>  }
>  
> +static void update_free_pages_stats(struct virtio_balloon *vb,
why _stats?
> +				unsigned long req_id)
> +{
> +	struct scatterlist sg_in, sg_out;
> +	unsigned long pfn = 0, bmap_len, max_pfn;
> +	struct virtqueue *vq = vb->misc_vq;
> +	struct balloon_bmap_hdr *hdr = vb->bmap_hdr;
> +	int ret = 1;
> +
> +	max_pfn = get_max_pfn();
> +	mutex_lock(&vb->balloon_lock);
> +	while (pfn < max_pfn) {
> +		memset(vb->page_bitmap, 0, vb->bmap_len);
> +		ret = get_free_pages(pfn, pfn + vb->pfn_limit,
> +			vb->page_bitmap, vb->bmap_len * BITS_PER_BYTE);
> +		hdr->cmd = cpu_to_virtio16(vb->vdev, BALLOON_GET_FREE_PAGES);
> +		hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
> +		hdr->req_id = cpu_to_virtio64(vb->vdev, req_id);
> +		hdr->start_pfn = cpu_to_virtio64(vb->vdev, pfn);
> +		bmap_len = vb->pfn_limit / BITS_PER_BYTE;
> +		if (!ret) {
> +			hdr->flag = cpu_to_virtio16(vb->vdev,
> +							BALLOON_FLAG_DONE);
> +			if (pfn + vb->pfn_limit > max_pfn)
> +				bmap_len = (max_pfn - pfn) / BITS_PER_BYTE;
> +		} else
> +			hdr->flag = cpu_to_virtio16(vb->vdev,
> +							BALLOON_FLAG_CONT);
> +		hdr->bmap_len = cpu_to_virtio64(vb->vdev, bmap_len);
> +		sg_init_one(&sg_out, hdr,
> +			 sizeof(struct balloon_bmap_hdr) + bmap_len);
Wait a second. This adds the same buffer multiple times in a loop.
We will overwrite the buffer without waiting for
hypervisor to process it. What did I miss?
> +
> +		virtqueue_add_outbuf(vq, &sg_out, 1, vb, GFP_KERNEL);
this can fail. you want to maybe make sure vq has enough space
before you use it or check error and wait.
> +		virtqueue_kick(vq);
why kick here within loop? wait until done. in fact kick
outside lock is better for smp.
> +		pfn += vb->pfn_limit;
> +	}
> +
> +	sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
> +	virtqueue_add_inbuf(vq, &sg_in, 1, &vb->req_hdr, GFP_KERNEL);
> +	virtqueue_kick(vq);
> +	mutex_unlock(&vb->balloon_lock);
> +}
> +
>  /*
>   * While most virtqueues communicate guest-initiated requests to the
hypervisor,
>   * the stats queue operates in reverse.  The driver initializes the
virtqueue
> @@ -511,18 +559,49 @@ static void update_balloon_size_func(struct
work_struct *work)
>  		queue_work(system_freezable_wq, work);
>  }
>  
> +static void misc_handle_rq(struct virtio_balloon *vb)
> +{
> +	struct balloon_req_hdr *ptr_hdr;
> +	unsigned int len;
> +
> +	ptr_hdr = virtqueue_get_buf(vb->misc_vq, &len);
> +	if (!ptr_hdr || len != sizeof(vb->req_hdr))
> +		return;
> +
> +	switch (ptr_hdr->cmd) {
> +	case BALLOON_GET_FREE_PAGES:
> +		update_free_pages_stats(vb, ptr_hdr->param);
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
> +static void misc_request(struct virtqueue *vq)
> +{
> +	struct virtio_balloon *vb = vq->vdev->priv;
> +
> +	misc_handle_rq(vb);
> +}
> +
>  static int init_vqs(struct virtio_balloon *vb)
>  {
> -	struct virtqueue *vqs[3];
> -	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
> -	static const char * const names[] = { "inflate",
"deflate", "stats" };
> +	struct virtqueue *vqs[4];
> +	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack,
> +					 stats_request, misc_request };
> +	static const char * const names[] = { "inflate",
"deflate", "stats",
> +						 "misc" };
>  	int err, nvqs;
>  
>  	/*
>  	 * We expect two virtqueues: inflate and deflate, and
>  	 * optionally stat.
>  	 */
> -	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 :
2;
> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ))
> +		nvqs = 4;
Does misc vq depend on stats vq feature then? if yes please validate that.

> +	else
> +		nvqs = virtio_has_feature(vb->vdev,
> +					  VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
Replace that ? with else too pls.
>  	err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs,
callbacks, names);
>  	if (err)
>  		return err;
> @@ -543,6 +622,16 @@ static int init_vqs(struct virtio_balloon *vb)
>  			BUG();
>  		virtqueue_kick(vb->stats_vq);
>  	}
> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_MISC_VQ)) {
> +		struct scatterlist sg_in;
> +
> +		vb->misc_vq = vqs[3];
> +		sg_init_one(&sg_in, &vb->req_hdr, sizeof(vb->req_hdr));
> +		if (virtqueue_add_inbuf(vb->misc_vq, &sg_in, 1,
> +		    &vb->req_hdr, GFP_KERNEL) < 0)
> +			BUG();
> +		virtqueue_kick(vb->misc_vq);
> +	}
>  	return 0;
>  }
>  
> @@ -639,8 +728,10 @@ static int virtballoon_probe(struct virtio_device
*vdev)
>  	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, GFP_KERNEL);
>  
>  	/* Clear the feature bit if memory allocation fails */
> -	if (!vb->bmap_hdr)
> +	if (!vb->bmap_hdr) {
>  		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
> +		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_MISC_VQ);
> +	}
>  	else
>  		vb->page_bitmap = vb->bmap_hdr + hdr_len;
>  	mutex_init(&vb->balloon_lock);
> @@ -743,6 +834,7 @@ static unsigned int features[] = {
>  	VIRTIO_BALLOON_F_STATS_VQ,
>  	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
>  	VIRTIO_BALLOON_F_PAGE_BITMAP,
> +	VIRTIO_BALLOON_F_MISC_VQ,
>  };
>  
>  static struct virtio_driver virtio_balloon_driver = {
> -- 
> 1.9.1

On Wed, Jul 27, 2016 at 09:23:33AM +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 at intel.com>
> Suggested-by: Michael S. Tsirkin <mst at redhat.com>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Amit Shah <amit.shah at redhat.com>
> ---
>  drivers/virtio/virtio_balloon.c | 184
+++++++++++++++++++++++++++++++++++-----
>  1 file changed, 162 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> index 8d649a2..2d18ff6 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -41,10 +41,28 @@
>  #define OOM_VBALLOON_DEFAULT_PAGES 256
>  #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
>  
> +/*
> + * VIRTIO_BALLOON_PFNS_LIMIT is used to limit the size of page bitmap
> + * to prevent a very large page bitmap, there are two reasons for this:
> + * 1) to save memory.
> + * 2) allocate a large bitmap may fail.
> + *
> + * The actual limit of pfn is determined by:
> + * pfn_limit = min(max_pfn, VIRTIO_BALLOON_PFNS_LIMIT);
> + *
> + * If system has more pages than VIRTIO_BALLOON_PFNS_LIMIT, we will scan
> + * the page list and send the PFNs with several times. To reduce the
> + * overhead of scanning the page list. VIRTIO_BALLOON_PFNS_LIMIT should
> + * be set with a value which can cover most cases.
> + */
> +#define VIRTIO_BALLOON_PFNS_LIMIT ((32 * (1ULL << 30)) >>
PAGE_SHIFT) /* 32GB */
> +
>  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);
> +
Please just include the correct header. No need for this hackery.
>  struct virtio_balloon {
>  	struct virtio_device *vdev;
>  	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> @@ -62,6 +80,15 @@ 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 length used to tell the host the pages */
> +	unsigned long *page_bitmap;
> +	unsigned long bmap_len;
> +	/* Pfn limit */
> +	unsigned long pfn_limit;
> +	/* 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.
> @@ -105,12 +132,45 @@ 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;
> +}
> +
>  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 = vb->bmap_hdr;
> +		unsigned long bmap_len;
> +
> +		/* cmd and req_id are not used here, set them to 0 */
> +		hdr->cmd = cpu_to_virtio16(vb->vdev, 0);
> +		hdr->page_shift = cpu_to_virtio16(vb->vdev, PAGE_SHIFT);
> +		hdr->reserved = cpu_to_virtio16(vb->vdev, 0);
> +		hdr->req_id = cpu_to_virtio64(vb->vdev, 0);
> +		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_init_one(&sg, hdr,
> +			 sizeof(struct balloon_bmap_hdr) + bmap_len);
> +	} 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. */
>  	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> @@ -118,7 +178,6 @@ 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 set_page_pfns(struct virtio_balloon *vb,
> @@ -133,13 +192,53 @@ static void set_page_pfns(struct virtio_balloon *vb,
>  					  page_to_balloon_pfn(page) + i);
>  }
>  
> -static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
> +static void set_page_bitmap(struct virtio_balloon *vb,
> +			 struct list_head *pages, struct virtqueue *vq)
> +{
> +	unsigned long pfn;
> +	struct page *page;
> +	bool found;
> +
> +	vb->min_pfn = rounddown(vb->min_pfn, BITS_PER_LONG);
> +	vb->max_pfn = roundup(vb->max_pfn, BITS_PER_LONG);
> +	for (pfn = vb->min_pfn; pfn < vb->max_pfn;
> +			pfn += vb->pfn_limit) {
> +		vb->start_pfn = pfn + vb->pfn_limit;
> +		vb->end_pfn = pfn;
> +		memset(vb->page_bitmap, 0, vb->bmap_len);
> +		found = false;
> +		list_for_each_entry(page, pages, lru) {
> +			unsigned long balloon_pfn = page_to_balloon_pfn(page);
> +
> +			if (balloon_pfn < pfn ||
> +				 balloon_pfn >= pfn + vb->pfn_limit)
> +				continue;
> +			set_bit(balloon_pfn - pfn, vb->page_bitmap);
> +			if (balloon_pfn > vb->end_pfn)
> +				vb->end_pfn = balloon_pfn;
> +			if (balloon_pfn < vb->start_pfn)
> +				vb->start_pfn = balloon_pfn;
> +			found = true;
> +		}
> +		if (found) {
> +			vb->start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG);
> +			vb->end_pfn = roundup(vb->end_pfn, BITS_PER_LONG);
> +			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;
> @@ -154,7 +253,10 @@ 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))
> @@ -163,8 +265,13 @@ 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;
> @@ -184,15 +291,19 @@ 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)
>  {
> -	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);
>  	for (vb->num_pfns = 0; vb->num_pfns < num;
> @@ -200,7 +311,10 @@ 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;
>  	}
> @@ -211,9 +325,14 @@ 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);
> -	release_pages_balloon(vb, &pages);
> +	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);
> +	}
>  	mutex_unlock(&vb->balloon_lock);
>  	return num_freed_pages;
>  }
> @@ -347,13 +466,15 @@ 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;
>  
> @@ -373,15 +494,17 @@ 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);
> +	use_bmap = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_PAGE_BITMAP);
>  	diff = towards_target(vb);
>  
>  	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)
> @@ -489,7 +612,7 @@ static int virtballoon_migratepage(struct
balloon_dev_info *vb_dev_info,
>  static int virtballoon_probe(struct virtio_device *vdev)
>  {
>  	struct virtio_balloon *vb;
> -	int err;
> +	int err, hdr_len;
>  
>  	if (!vdev->config->get) {
>  		dev_err(&vdev->dev, "%s failure: config access
disabled\n",
> @@ -508,6 +631,18 @@ static int virtballoon_probe(struct virtio_device
*vdev)
>  	spin_lock_init(&vb->stop_update_lock);
>  	vb->stop_update = false;
>  	vb->num_pages = 0;
> +	vb->pfn_limit = VIRTIO_BALLOON_PFNS_LIMIT;
> +	vb->pfn_limit = min(vb->pfn_limit, get_max_pfn());
> +	vb->bmap_len = ALIGN(vb->pfn_limit, BITS_PER_LONG) /
> +		 BITS_PER_BYTE + 2 * sizeof(unsigned long);
> +	hdr_len = sizeof(struct balloon_bmap_hdr);
> +	vb->bmap_hdr = kzalloc(hdr_len + vb->bmap_len, 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 = vb->bmap_hdr + hdr_len;
>  	mutex_init(&vb->balloon_lock);
>  	init_waitqueue_head(&vb->acked);
>  	vb->vdev = vdev;
> @@ -541,9 +676,12 @@ out:
>  
>  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. */
> @@ -565,6 +703,7 @@ 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);
>  }
>  
> @@ -603,6 +742,7 @@ 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 = {
> -- 
> 1.9.1

On Wed, Jul 27, 2016 at 09:23:32AM +0800, Liang Li
wrote:
> Expose the function to get the max pfn, so it can be used in the
> virtio-balloon device driver.
> 
> Signed-off-by: Liang Li <liang.z.li at intel.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Amit Shah <amit.shah at redhat.com>
> ---
>  mm/page_alloc.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8b3e134..7da61ad 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4517,6 +4517,12 @@ void show_free_areas(unsigned int filter)
>  	show_swap_cache_info();
>  }
>  
> +unsigned long get_max_pfn(void)
> +{
> +	return max_pfn;
> +}
> +EXPORT_SYMBOL(get_max_pfn);
> +

This needs a coment that this can change at any time.
So it's only good as a hint e.g. for sizing data structures.
>  static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
>  {
>  	zoneref->zone = zone;
> -- 
> 1.9.1

On Wed, Jul 27, 2016 at 09:23:35AM +0800, Liang Li
wrote:
> Save the free page info into a page bitmap, will be used in virtio
> balloon device driver.
> 
> Signed-off-by: Liang Li <liang.z.li at intel.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: Cornelia Huck <cornelia.huck at de.ibm.com>
> Cc: Amit Shah <amit.shah at redhat.com>
> ---
>  mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7da61ad..3ad8b10 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4523,6 +4523,52 @@ unsigned long get_max_pfn(void)
>  }
>  EXPORT_SYMBOL(get_max_pfn);
>  
> +static void mark_free_pages_bitmap(struct zone *zone, unsigned long
start_pfn,
> +	unsigned long end_pfn, unsigned long *bitmap, unsigned long len)
> +{
> +	unsigned long pfn, flags, page_num;
> +	unsigned int order, t;
> +	struct list_head *curr;
> +
> +	if (zone_is_empty(zone))
> +		return;
> +	end_pfn = min(start_pfn + len, end_pfn);
> +	spin_lock_irqsave(&zone->lock, flags);
> +
> +	for_each_migratetype_order(order, t) {
Why not do each order separately? This way you can
use a single bit to pass a huge page to host.

Not a requirement but hey.

Alternatively (and maybe that is a better idea0
if you wanted to, you could just skip lone 4K pages.
It's not clear that they are worth bothering with.
Add a flag to start with some reasonably large order and go from there.

> +		list_for_each(curr, &zone->free_area[order].free_list[t]) {
> +			pfn = page_to_pfn(list_entry(curr, struct page, lru));
> +			if (pfn >= start_pfn && pfn <= end_pfn) {
> +				page_num = 1UL << order;
> +				if (pfn + page_num > end_pfn)
> +					page_num = end_pfn - pfn;
> +				bitmap_set(bitmap, pfn - start_pfn, page_num);
> +			}
> +		}
> +	}
> +
> +	spin_unlock_irqrestore(&zone->lock, flags);
> +}
> +
> +int get_free_pages(unsigned long start_pfn, unsigned long end_pfn,
> +		unsigned long *bitmap, unsigned long len)
> +{
> +	struct zone *zone;
> +	int ret = 0;
> +
> +	if (bitmap == NULL || start_pfn > end_pfn || start_pfn >= max_pfn)
> +		return 0;
> +	if (end_pfn < max_pfn)
> +		ret = 1;
> +	if (end_pfn >= max_pfn)
> +		ret = 0;
> +
> +	for_each_populated_zone(zone)
> +		mark_free_pages_bitmap(zone, start_pfn, end_pfn, bitmap, len);
> +	return ret;
> +}
> +EXPORT_SYMBOL(get_free_pages);
> +
>  static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
>  {
>  	zoneref->zone = zone;
> -- 
> 1.9.1