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@xxxxxxxxx>
---
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();
+ bmap_bytes = ALIGN(max_pfn, BITS_PER_LONG) / BITS_PER_BYTE;
+ if (!vb->page_bitmap)
+ vb->page_bitmap = kzalloc(bmap_bytes, GFP_KERNEL);
+ 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;
+}
+
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)) {
+ 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);
+ 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);
+ }
+
+ 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)
--
1.9.1
--
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