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

Michael S. Tsirkin
2020-03-26T07:18:09Z

First, either QEMU or Linux version of any interface changes
should be copied to the virtio TC.

:

On Mon, Mar 23, 2020 at 12:04:56AM +0800, Hui Zhu wrote:
> 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>

I'd like to repeat my original idea of doing large page allocations
unconditionally within guest.

> ---
> 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)
> {

Hmm no this is not what was previously suggested. David Hildenbrand proposed
starting with highest order and iterating until we reach 0.
And I proposed a new API to allocate some memory between min and max
orders.

> @@ -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