[PATCH for Linux v2] virtio_balloon: Add VIRTIO_BALLOON_VQ_INFLATE_CONT to handle THP split issue

Hui Zhu
2020-03-22T16:13:05Z

The first version is in [1].
According to the comments from Michael and David, I updated the patch.
1. Added a separate vq inflate_cont_vq to transport inflate continuous
pages.
2. Set all the pages in the continuous pages movable then they can be
compaction.
3. Added a new element pages_order to virtio_balloon_config. It is the
inflate pages order that is set by the QEMU.
4. If the balloon cannot get any continuous pages from the system.
Go back to use the single page to fill the balloon.
5. Use balloon_pages_alloc to allocate the single page and continuous
pages. Replace __GFP_NORETRY with __GFP_RETRY_MAYFAIL when allocating
the continuous pages because it can increase the success rate of
allocating large chunks of memory.

Following is the introduction of the function.
If the guest kernel has many fragmentation pages, use virtio_balloon
will split THP of QEMU when it calls MADV_DONTNEED madvise to release
the balloon pages.
This is an example in a VM with 1G memory 1CPU:
// This is the THP number before VM execution in the host.
// None use THP.
cat /proc/meminfo | grep AnonHugePages:
AnonHugePages: 0 kB

// After VM start, use usemem
// (https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git)
// punch-holes function generates 400m fragmentation pages in the guest
// kernel.
usemem --punch-holes -s -1 800m &

// This is the THP number after this command in the host.
// Some THP is used by VM because usemem will access 800M memory
// in the guest.
cat /proc/meminfo | grep AnonHugePages:
AnonHugePages: 976896 kB

// Connect to the QEMU monitor, setup balloon, and set it size to 600M.
(qemu) device_add virtio-balloon-pci,id=balloon1
(qemu) info balloon
balloon: actual=1024
(qemu) balloon 600
(qemu) info balloon
balloon: actual=600

// This is the THP number after inflate the balloon in the host.
cat /proc/meminfo | grep AnonHugePages:
AnonHugePages: 151552 kB

THP number decreased more than 800M.
The reason is usemem with punch-holes option will free every other
page after allocation. Then 400M free memory inside the guest kernel
is fragmentation pages.
The guest kernel will use them to inflate the balloon. When these
fragmentation pages are freed, THP will be split.

This commit tries to handle this with add a new flag
VIRTIO_BALLOON_VQ_INFLATE_CONT.
When this flag is set, the balloon will try to use continuous pages
inflate the balloon. And the pages order is set to THP order.
Then THP pages will be freed together in the host.
This is an example in a VM with 1G memory 1CPU:
// This is the THP number before VM execution in the host.
// None use THP.
cat /proc/meminfo | grep AnonHugePages:
AnonHugePages: 0 kB

// After VM start, use usemem punch-holes function generates 400M
// fragmentation pages in the guest kernel.
usemem --punch-holes -s -1 800m &

// This is the THP number after this command in the host.
// Some THP is used by VM because usemem will access 800M memory
// in the guest.
cat /proc/meminfo | grep AnonHugePages:
AnonHugePages: 976896 kB

// Connect to the QEMU monitor, setup balloon, and set it size to 600M.
(qemu) device_add virtio-balloon-pci,id=balloon1,cont-pages=on
(qemu) info balloon
balloon: actual=1024
(qemu) balloon 600
(qemu) info balloon
balloon: actual=600

// This is the THP number after inflate the balloon in the host.
cat /proc/meminfo | grep AnonHugePages:
AnonHugePages: 610304 kB

The THP number decreases 358M. This shows that
VIRTIO_BALLOON_VQ_INFLATE_CONT can help handle the THP split issue.

[1] https://lkml.org/lkml/2020/3/12/144

Signed-off-by: Hui Zhu <teawaterz@linux.alibaba.com>
---
drivers/virtio/virtio_balloon.c | 78 ++++++++++++++++++++++++++++++-------
include/linux/balloon_compaction.h | 9 ++++-
include/uapi/linux/virtio_balloon.h | 3 ++
mm/balloon_compaction.c | 40 +++++++++++++++----
4 files changed, 109 insertions(+), 21 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 341458f..fbd2b02f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -47,6 +47,7 @@ enum virtio_balloon_vq {
VIRTIO_BALLOON_VQ_DEFLATE,
VIRTIO_BALLOON_VQ_STATS,
VIRTIO_BALLOON_VQ_FREE_PAGE,
+ VIRTIO_BALLOON_VQ_INFLATE_CONT,
VIRTIO_BALLOON_VQ_MAX
};

@@ -56,7 +57,8 @@ enum virtio_balloon_config_read {

struct virtio_balloon {
struct virtio_device *vdev;
- struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
+ struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq,
+ *inflate_cont_vq;

/* Balloon's own wq for cpu-intensive work items */
struct workqueue_struct *balloon_wq;
@@ -114,6 +116,12 @@ struct virtio_balloon {

/* To register a shrinker to shrink memory upon memory pressure */
struct shrinker shrinker;
+
+ /* Pages order if VIRTIO_BALLOON_F_CONT_PAGES is set.
+ * if VIRTIO_BALLOON_F_CONT_PAGES is not set,
+ * pages_order will be set to 0.
+ */
+ __u32 pages_order;
};

static struct virtio_device_id id_table[] = {
@@ -169,10 +177,11 @@ 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 unsigned int fill_balloon_order(struct virtio_balloon *vb, size_t num,
+ unsigned int order)
{
- unsigned num_allocated_pages;
- unsigned num_pfns;
+ unsigned int num_allocated_pages;
+ unsigned int num_pfns;
struct page *page;
LIST_HEAD(pages);

@@ -181,12 +190,12 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)

for (num_pfns = 0; num_pfns < num;
num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
- struct page *page = balloon_page_alloc();
+ struct page *page = balloon_pages_alloc(order);

if (!page) {
dev_info_ratelimited(&vb->vdev->dev,
- "Out of puff! Can't get %u pages\n",
- VIRTIO_BALLOON_PAGES_PER_PAGE);
+ "Out of puff! Can't get %u pages\n",
+ VIRTIO_BALLOON_PAGES_PER_PAGE << order);
/* Sleep for at least 1/5 of a second before retry. */
msleep(200);
break;
@@ -200,25 +209,48 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
vb->num_pfns = 0;

while ((page = balloon_page_pop(&pages))) {
- balloon_page_enqueue(&vb->vb_dev_info, page);
+ balloon_pages_enqueue(&vb->vb_dev_info, page, order);

set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
- vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
+ vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE << order;
if (!virtio_has_feature(vb->vdev,
VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
- adjust_managed_page_count(page, -1);
+ adjust_managed_page_count(page, -(1 << order));
vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
}

- num_allocated_pages = vb->num_pfns;
+ num_allocated_pages = vb->num_pfns << order;
/* Did we get any? */
- if (vb->num_pfns != 0)
- tell_host(vb, vb->inflate_vq);
+ if (vb->num_pfns != 0) {
+ if (order)
+ tell_host(vb, vb->inflate_cont_vq);
+ else
+ tell_host(vb, vb->inflate_vq);
+ }
mutex_unlock(&vb->balloon_lock);

return num_allocated_pages;
}

+static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num)
+{
+ unsigned int num_allocated_pages = 0;
+
+ if (vb->pages_order) {
+ num_allocated_pages = fill_balloon_order(vb, num,
+ vb->pages_order);
+ if (!num_allocated_pages)
+ dev_info_ratelimited(&vb->vdev->dev,
+ "Fail get any continuous pages in order %u\n",
+ vb->pages_order);
+ }
+
+ if (!num_allocated_pages)
+ num_allocated_pages = fill_balloon_order(vb, num, 0);
+
+ return num_allocated_pages;
+}
+
static void release_pages_balloon(struct virtio_balloon *vb,
struct list_head *pages)
{
@@ -481,6 +513,8 @@ static int init_vqs(struct virtio_balloon *vb)
names[VIRTIO_BALLOON_VQ_STATS] = NULL;
callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+ callbacks[VIRTIO_BALLOON_VQ_INFLATE_CONT] = NULL;
+ names[VIRTIO_BALLOON_VQ_INFLATE_CONT] = NULL;

if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
names[VIRTIO_BALLOON_VQ_STATS] = "stats";
@@ -492,6 +526,11 @@ static int init_vqs(struct virtio_balloon *vb)
callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
}

+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CONT_PAGES)) {
+ names[VIRTIO_BALLOON_VQ_INFLATE_CONT] = "inflate_cont";
+ callbacks[VIRTIO_BALLOON_VQ_INFLATE_CONT] = balloon_ack;
+ }
+
err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
vqs, callbacks, names, NULL, NULL);
if (err)
@@ -524,6 +563,10 @@ static int init_vqs(struct virtio_balloon *vb)
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];

+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CONT_PAGES))
+ vb->inflate_cont_vq
+ = vqs[VIRTIO_BALLOON_VQ_INFLATE_CONT];
+
return 0;
}

@@ -945,6 +988,14 @@ static int virtballoon_probe(struct virtio_device *vdev)
if (err)
goto out_del_balloon_wq;
}
+ if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CONT_PAGES)) {
+ virtio_cread(vb->vdev, struct virtio_balloon_config,
+ pages_order, &vb->pages_order);
+ if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
+ vb->pages_order
+ = le32_to_cpu((__force __le32)vb->pages_order);
+ } else
+ vb->pages_order = 0;
virtio_device_ready(vdev);

if (towards_target(vb))
@@ -1058,6 +1109,7 @@ static unsigned int features[] = {
VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
VIRTIO_BALLOON_F_FREE_PAGE_HINT,
VIRTIO_BALLOON_F_PAGE_POISON,
+ VIRTIO_BALLOON_F_CONT_PAGES,
};

static struct virtio_driver virtio_balloon_driver = {
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 338aa27..8180bbf 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -60,15 +60,22 @@ struct balloon_dev_info {
struct inode *inode;
};

-extern struct page *balloon_page_alloc(void);
+extern struct page *balloon_pages_alloc(unsigned int order);
extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
struct page *page);
+extern void balloon_pages_enqueue(struct balloon_dev_info *b_dev_info,
+ struct page *page, unsigned int order);
extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
struct list_head *pages);
extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
struct list_head *pages, size_t n_req_pages);

+static inline struct page *balloon_page_alloc(void)
+{
+ return balloon_pages_alloc(0);
+}
+
static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
{
balloon->isolated_pages = 0;
diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
index a1966cd7..e21b0aa 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -36,6 +36,7 @@
#define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
#define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */
#define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */
+#define VIRTIO_BALLOON_F_CONT_PAGES 5 /* VQ to report continuous pages */

/* Size of a PFN in the balloon interface. */
#define VIRTIO_BALLOON_PFN_SHIFT 12
@@ -51,6 +52,8 @@ struct virtio_balloon_config {
__u32 free_page_report_cmd_id;
/* Stores PAGE_POISON if page poisoning is in use */
__u32 poison_val;
+ /* Pages order if VIRTIO_BALLOON_F_CONT_PAGES is set */
+ __u32 pages_order;
};

#define VIRTIO_BALLOON_S_SWAP_IN 0 /* Amount of memory swapped in */
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 26de020..87df4b2 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -112,8 +112,8 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);

/*
- * balloon_page_alloc - allocates a new page for insertion into the balloon
- * page list.
+ * balloon_pages_alloc - allocates a new page for insertion into the balloon
+ * page list.
*
* Driver must call this function to properly allocate a new balloon page.
* Driver must call balloon_page_enqueue before definitively removing the page
@@ -121,14 +121,21 @@ EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
*
* Return: struct page for the allocated page or NULL on allocation failure.
*/
-struct page *balloon_page_alloc(void)
+struct page *balloon_pages_alloc(unsigned int order)
{
- struct page *page = alloc_page(balloon_mapping_gfp_mask() |
- __GFP_NOMEMALLOC | __GFP_NORETRY |
- __GFP_NOWARN);
+ gfp_t gfp_mask;
+
+ if (order > 1)
+ gfp_mask = __GFP_RETRY_MAYFAIL;
+ else
+ gfp_mask = __GFP_NORETRY;
+
+ struct page *page = alloc_pages(balloon_mapping_gfp_mask() |
+ gfp_mask | __GFP_NOMEMALLOC |
+ __GFP_NOWARN, order);
return page;
}
-EXPORT_SYMBOL_GPL(balloon_page_alloc);
+EXPORT_SYMBOL_GPL(balloon_pages_alloc);

/*
* balloon_page_enqueue - inserts a new page into the balloon page list.
@@ -155,6 +162,25 @@ void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
EXPORT_SYMBOL_GPL(balloon_page_enqueue);

/*
+ * balloon_pages_enqueue - inserts continuous pages into the balloon page list.
+ */
+void balloon_pages_enqueue(struct balloon_dev_info *b_dev_info,
+ struct page *page, unsigned int order)
+{
+ unsigned long flags;
+ unsigned long pfn = page_to_pfn(page);
+ unsigned long last_pfn = pfn + (1 << order) - 1;
+
+ spin_lock_irqsave(&b_dev_info->pages_lock, flags);
+ for (; pfn <= last_pfn; pfn++) {
+ page = pfn_to_page(pfn);
+ balloon_page_enqueue_one(b_dev_info, page);
+ }
+ spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+}
+EXPORT_SYMBOL_GPL(balloon_pages_enqueue);
+
+/*
* balloon_page_dequeue - removes a page from balloon's page list and returns
* its address to allow the driver to release the page.
* @b_dev_info: balloon device decriptor where we will grab a page from.
--
2.7.4