On Wed, Nov 07, 2012 at 01:05:52AM -0200, Rafael Aquini wrote:
> Memory fragmentation introduced by ballooning might reduce significantly
> the number of 2MB contiguous memory blocks that can be used within a guest,
> thus imposing performance penalties associated with the reduced number of
> transparent huge pages that could be used by the guest workload.
>
> Besides making balloon pages movable at allocation time and introducing
> the necessary primitives to perform balloon page migration/compaction,
> this patch also introduces the following locking scheme, in order to
> enhance the syncronization methods for accessing elements of struct
> virtio_balloon, thus providing protection against concurrent access
> introduced by parallel memory migration threads.
>
> - balloon_lock (mutex) : synchronizes the access demand to elements of
> struct virtio_balloon and its queue operations;
>
> Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_balloon.c | 135 ++++++++++++++++++++++++++++++++++++----
> 1 file changed, 123 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 0908e60..69eede7 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -27,6 +27,7 @@
> #include <linux/delay.h>
> #include <linux/slab.h>
> #include <linux/module.h>
> +#include <linux/balloon_compaction.h>
>
> /*
> * Balloon device works in 4K page units. So each page is pointed to by
> @@ -34,6 +35,7 @@
> * page units.
> */
> #define VIRTIO_BALLOON_PAGES_PER_PAGE (PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
> +#define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
>
> struct virtio_balloon
> {
> @@ -52,15 +54,19 @@ struct virtio_balloon
> /* Number of balloon pages we've told the Host we're not using. */
> unsigned int num_pages;
> /*
> - * The pages we've told the Host we're not using.
> + * The pages we've told the Host we're not using are enqueued
> + * at vb_dev_info->pages list.
> * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
> * to num_pages above.
> */
> - struct list_head pages;
> + struct balloon_dev_info *vb_dev_info;
> +
> + /* Synchronize access/update to this struct virtio_balloon elements */
> + struct mutex balloon_lock;
>
> /* The array of pfns we tell the Host about. */
> unsigned int num_pfns;
> - u32 pfns[256];
> + u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
>
> /* Memory statistics */
> int need_stats_update;
> @@ -122,18 +128,25 @@ static void set_page_pfns(u32 pfns[], struct page *page)
>
> static void fill_balloon(struct virtio_balloon *vb, size_t num)
> {
> + struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
> +
> + static DEFINE_RATELIMIT_STATE(fill_balloon_rs,
> + DEFAULT_RATELIMIT_INTERVAL,
> + DEFAULT_RATELIMIT_BURST);
> +
> /* 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;
> vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> - struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
> - __GFP_NOMEMALLOC | __GFP_NOWARN);
> + struct page *page = balloon_page_enqueue(vb_dev_info);
> +
> if (!page) {
> - if (printk_ratelimit())
> + if (__ratelimit(&fill_balloon_rs))
> dev_printk(KERN_INFO, &vb->vdev->dev,
> "Out of puff! Can't get %zu pages\n",
> - num);
> + VIRTIO_BALLOON_PAGES_PER_PAGE);
> /* Sleep for at least 1/5 of a second before retry. */
> msleep(200);
> break;
> @@ -141,7 +154,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
> set_page_pfns(vb->pfns + vb->num_pfns, page);
> vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
> totalram_pages--;
> - list_add(&page->lru, &vb->pages);
> }
>
> /* Didn't get any? Oh well. */
> @@ -149,6 +161,7 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num)
> return;
>
> tell_host(vb, vb->inflate_vq);
> + mutex_unlock(&vb->balloon_lock);
> }
>
> static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
> @@ -165,14 +178,17 @@ static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
> static void leak_balloon(struct virtio_balloon *vb, size_t num)
> {
> struct page *page;
> + struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
>
> /* 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;
> vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
> - page = list_first_entry(&vb->pages, struct page, lru);
> - list_del(&page->lru);
> + page = balloon_page_dequeue(vb_dev_info);
> + if (!page)
> + break;
> set_page_pfns(vb->pfns + vb->num_pfns, page);
> vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
> }
> @@ -183,6 +199,7 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> * is true, we *have* to do it in this order
> */
> tell_host(vb, vb->deflate_vq);
> + mutex_unlock(&vb->balloon_lock);
> release_pages_by_pfn(vb->pfns, vb->num_pfns);
> }
>
> @@ -339,9 +356,76 @@ static int init_vqs(struct virtio_balloon *vb)
> return 0;
> }
>
> +static const struct address_space_operations virtio_balloon_aops;
> +#ifdef CONFIG_BALLOON_COMPACTION
> +/*
> + * virtballoon_migratepage - perform the balloon page migration on behalf of
> + * a compation thread. (called under page lock)
> + * @mapping: the page->mapping which will be assigned to the new migrated page.
> + * @newpage: page that will replace the isolated page after migration finishes.
> + * @page : the isolated (old) page that is about to be migrated to newpage.
> + * @mode : compaction mode -- not used for balloon page migration.
> + *
> + * After a ballooned page gets isolated by compaction procedures, this is the
> + * function that performs the page migration on behalf of a compaction thread
> + * The page migration for virtio balloon is done in a simple swap fashion which
> + * follows these two macro steps:
> + * 1) insert newpage into vb->pages list and update the host about it;
> + * 2) update the host about the old page removed from vb->pages list;
> + *
> + * This function preforms the balloon page migration task.
> + * Called through balloon_mapping->a_ops->migratepage
> + */
> +int virtballoon_migratepage(struct address_space *mapping,
> + struct page *newpage, struct page *page, enum migrate_mode mode)
> +{
> + struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
> + struct virtio_balloon *vb;
> + unsigned long flags;
> +
> + BUG_ON(!vb_dev_info);
> +
> + vb = vb_dev_info->balloon_device;
> +
> + if (!mutex_trylock(&vb->balloon_lock))
> + return -EAGAIN;
> +
> + /* balloon's page migration 1st step -- inflate "newpage" */
> + spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
> + balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
> + vb_dev_info->isolated_pages--;
> + spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
> + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> + set_page_pfns(vb->pfns, newpage);
> + tell_host(vb, vb->inflate_vq);
> +
> + /*
> + * balloon's page migration 2nd step -- deflate "page"
> + *
> + * It's safe to delete page->lru here because this page is at
> + * an isolated migration list, and this step is expected to happen here
> + */
> + balloon_page_delete(page);
> + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
> + set_page_pfns(vb->pfns, page);
> + tell_host(vb, vb->deflate_vq);
> +
> + mutex_unlock(&vb->balloon_lock);
> +
> + return MIGRATEPAGE_BALLOON_SUCCESS;
> +}
> +
> +/* define the balloon_mapping->a_ops callback to allow balloon page migration */
> +static const struct address_space_operations virtio_balloon_aops = {
> + .migratepage = virtballoon_migratepage,
> +};
> +#endif /* CONFIG_BALLOON_COMPACTION */
> +
> static int virtballoon_probe(struct virtio_device *vdev)
> {
> struct virtio_balloon *vb;
> + struct address_space *vb_mapping;
> + struct balloon_dev_info *vb_devinfo;
> int err;
>
> vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
> @@ -350,16 +434,37 @@ static int virtballoon_probe(struct virtio_device *vdev)
> goto out;
> }
>
> - INIT_LIST_HEAD(&vb->pages);
> vb->num_pages = 0;
> + mutex_init(&vb->balloon_lock);
> init_waitqueue_head(&vb->config_change);
> init_waitqueue_head(&vb->acked);
> vb->vdev = vdev;
> vb->need_stats_update = 0;
>
> + vb_devinfo = balloon_devinfo_alloc(vb);
> + if (IS_ERR(vb_devinfo)) {
> + err = PTR_ERR(vb_devinfo);
> + goto out_free_vb;
> + }
> +
> + vb_mapping = balloon_mapping_alloc(vb_devinfo,
> + (balloon_compaction_check()) ?
> + &virtio_balloon_aops : NULL);
> + if (IS_ERR(vb_mapping)) {
> + /*
> + * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
> + * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
> + */
> + err = PTR_ERR(vb_mapping);
> + if (err != -EOPNOTSUPP)
> + goto out_free_vb_devinfo;
> + }
> +
> + vb->vb_dev_info = vb_devinfo;
> +
> err = init_vqs(vb);
> if (err)
> - goto out_free_vb;
> + goto out_free_vb_mapping;
>
> vb->thread = kthread_run(balloon, vb, "vballoon");
> if (IS_ERR(vb->thread)) {
> @@ -371,6 +476,10 @@ static int virtballoon_probe(struct virtio_device *vdev)
>
> out_del_vqs:
> vdev->config->del_vqs(vdev);
> +out_free_vb_mapping:
> + balloon_mapping_free(vb_mapping);
> +out_free_vb_devinfo:
> + balloon_devinfo_free(vb_devinfo);
> out_free_vb:
> kfree(vb);
> out:
> @@ -396,6 +505,8 @@ static void __devexit virtballoon_remove(struct virtio_device *vdev)
>
> kthread_stop(vb->thread);
> remove_common(vb);
> + balloon_mapping_free(vb->vb_dev_info->mapping);
> + balloon_devinfo_free(vb->vb_dev_info);
> kfree(vb);
> }
>
> --
> 1.7.11.7
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