Re: [RFC][Patch v11 2/2] virtio-balloon: page_hinting: reporting to the host

[Nitesh Narayan Lal <nitesh@redhat.com>]

On 7/24/19 3:47 PM, Michael S. Tsirkin wrote:
> On Wed, Jul 10, 2019 at 03:51:58PM -0400, Nitesh Narayan Lal wrote:
>> Enables the kernel to negotiate VIRTIO_BALLOON_F_HINTING feature with the
>> host. If it is available and page_hinting_flag is set to true, page_hinting
>> is enabled and its callbacks are configured along with the max_pages count
>> which indicates the maximum number of pages that can be isolated and hinted
>> at a time. Currently, only free pages of order >= (MAX_ORDER - 2) are
>> reported. To prevent any false OOM max_pages count is set to 16.
>>
>> By default page_hinting feature is enabled and gets loaded as soon
>> as the virtio-balloon driver is loaded. However, it could be disabled
>> by writing the page_hinting_flag which is a virtio-balloon parameter.
>>
>> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
>> ---
>>  drivers/virtio/Kconfig              |  1 +
>>  drivers/virtio/virtio_balloon.c     | 91 ++++++++++++++++++++++++++++-
>>  include/uapi/linux/virtio_balloon.h | 11 ++++
>>  3 files changed, 102 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
>> index 023fc3bc01c6..dcc0cb4269a5 100644
>> --- a/drivers/virtio/Kconfig
>> +++ b/drivers/virtio/Kconfig
>> @@ -47,6 +47,7 @@ config VIRTIO_BALLOON
>>  	tristate "Virtio balloon driver"
>>  	depends on VIRTIO
>>  	select MEMORY_BALLOON
>> +	select PAGE_HINTING
>>  	---help---
>>  	 This driver supports increasing and decreasing the amount
>>  	 of memory within a KVM guest.
>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
>> index 44339fc87cc7..1fb0eb0b2c20 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/mount.h>
>>  #include <linux/magic.h>
>> +#include <linux/page_hinting.h>
>>  
>>  /*
>>   * Balloon device works in 4K page units.  So each page is pointed to by
>> @@ -35,6 +36,12 @@
>>  /* The size of a free page block in bytes */
>>  #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
>>  	(1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
>> +/* Number of isolated pages to be reported to the host at a time.
>> + * TODO:
>> + * 1. Set it via host.
>> + * 2. Find an optimal value for this.
>> + */
>> +#define PAGE_HINTING_MAX_PAGES	16
>>  
>>  #ifdef CONFIG_BALLOON_COMPACTION
>>  static struct vfsmount *balloon_mnt;
>> @@ -45,6 +52,7 @@ enum virtio_balloon_vq {
>>  	VIRTIO_BALLOON_VQ_DEFLATE,
>>  	VIRTIO_BALLOON_VQ_STATS,
>>  	VIRTIO_BALLOON_VQ_FREE_PAGE,
>> +	VIRTIO_BALLOON_VQ_HINTING,
>>  	VIRTIO_BALLOON_VQ_MAX
>>  };
>>  
>> @@ -54,7 +62,8 @@ 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,
>> +			 *hinting_vq;
>>  
>>  	/* Balloon's own wq for cpu-intensive work items */
>>  	struct workqueue_struct *balloon_wq;
>> @@ -112,6 +121,9 @@ struct virtio_balloon {
>>  
>>  	/* To register a shrinker to shrink memory upon memory pressure */
>>  	struct shrinker shrinker;
>> +
>> +	/* Array object pointing at the isolated pages ready for hinting */
>> +	struct isolated_memory isolated_pages[PAGE_HINTING_MAX_PAGES];
>>  };
>>  
>>  static struct virtio_device_id id_table[] = {
>> @@ -119,6 +131,66 @@ static struct virtio_device_id id_table[] = {
>>  	{ 0 },
>>  };
>>  
>> +static struct page_hinting_config page_hinting_conf;
>> +bool page_hinting_flag = true;
>> +struct virtio_balloon *hvb;
>> +module_param(page_hinting_flag, bool, 0444);
>> +MODULE_PARM_DESC(page_hinting_flag, "Enable page hinting");
>> +
>> +static int page_hinting_report(void)
>> +{
>> +	struct virtqueue *vq = hvb->hinting_vq;
>> +	struct scatterlist sg;
>> +	int err = 0, unused;
>> +
>> +	mutex_lock(&hvb->balloon_lock);
>> +	sg_init_one(&sg, hvb->isolated_pages, sizeof(hvb->isolated_pages[0]) *
>> +		    PAGE_HINTING_MAX_PAGES);
>> +	err = virtqueue_add_outbuf(vq, &sg, 1, hvb, GFP_KERNEL);
> In Alex's patch, I really like it that he's passing pages as sg
> entries. IMHO that's both cleaner and allows seamless
> support for arbitrary page sizes.
>
> In particular ....
+1. I will also incorporate this change.
>
>> +	if (!err)
>> +		virtqueue_kick(hvb->hinting_vq);
>> +	wait_event(hvb->acked, virtqueue_get_buf(vq, &unused));
>> +	mutex_unlock(&hvb->balloon_lock);
>> +	return err;
>> +}
>> +
>> +void hint_pages(struct list_head *pages)
>> +{
>> +	struct device *dev = &hvb->vdev->dev;
>> +	struct page *page, *next;
>> +	int idx = 0, order, err;
>> +	unsigned long pfn;
>> +
>> +	list_for_each_entry_safe(page, next, pages, lru) {
>> +		pfn = page_to_pfn(page);
>> +		order = page_private(page);
>> +		hvb->isolated_pages[idx].phys_addr = pfn << PAGE_SHIFT;
>> +		hvb->isolated_pages[idx].size = (1 << order) * PAGE_SIZE;
>> +		idx++;
> ... passing native endian-ness values to host creates pain for
> cross-endian configurations.
>
>> +	}
>> +	err = page_hinting_report();
>> +	if (err < 0)
>> +		dev_err(dev, "Failed to hint pages, err = %d\n", err);
>> +}
>> +
>> +static void page_hinting_init(struct virtio_balloon *vb)
>> +{
>> +	struct device *dev = &vb->vdev->dev;
>> +	int err;
>> +
>> +	page_hinting_conf.hint_pages = hint_pages;
>> +	page_hinting_conf.max_pages = PAGE_HINTING_MAX_PAGES;
>> +	err = page_hinting_enable(&page_hinting_conf);
>> +	if (err < 0) {
>> +		dev_err(dev, "Failed to enable page-hinting, err = %d\n", err);
> It would be nicer to disable the feature bit then, or fail probe
> completely.
Makes sense. Thanks.
>> +		page_hinting_flag = false;
>> +		page_hinting_conf.hint_pages = NULL;
>> +		page_hinting_conf.max_pages = 0;
>> +		return;
>> +	}
>> +	hvb = vb;
>> +}
>> +
>>  static u32 page_to_balloon_pfn(struct page *page)
>>  {
>>  	unsigned long pfn = page_to_pfn(page);
>> @@ -475,6 +547,7 @@ static int init_vqs(struct virtio_balloon *vb)
>>  	names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
>>  	names[VIRTIO_BALLOON_VQ_STATS] = NULL;
>>  	names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
>> +	names[VIRTIO_BALLOON_VQ_HINTING] = NULL;
>>  
>>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>>  		names[VIRTIO_BALLOON_VQ_STATS] = "stats";
>> @@ -486,11 +559,18 @@ static int init_vqs(struct virtio_balloon *vb)
>>  		callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
>>  	}
>>  
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) {
>> +		names[VIRTIO_BALLOON_VQ_HINTING] = "hinting_vq";
>> +		callbacks[VIRTIO_BALLOON_VQ_HINTING] = balloon_ack;
>> +	}
>>  	err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
>>  					 vqs, callbacks, names, NULL, NULL);
>>  	if (err)
>>  		return err;
>>  
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING))
>> +		vb->hinting_vq = vqs[VIRTIO_BALLOON_VQ_HINTING];
>> +
>>  	vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
>>  	vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
>>  	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>> @@ -929,6 +1009,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
>>  		if (err)
>>  			goto out_del_balloon_wq;
>>  	}
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING) &&
>> +	    page_hinting_flag)
>> +		page_hinting_init(vb);
>>  	virtio_device_ready(vdev);
>>  
>>  	if (towards_target(vb))
>> @@ -976,6 +1059,10 @@ static void virtballoon_remove(struct virtio_device *vdev)
>>  		destroy_workqueue(vb->balloon_wq);
>>  	}
>>  
>> +	if (!page_hinting_flag) {
>> +		hvb = NULL;
>> +		page_hinting_disable();
>> +	}
>>  	remove_common(vb);
>>  #ifdef CONFIG_BALLOON_COMPACTION
>>  	if (vb->vb_dev_info.inode)
>> @@ -1030,8 +1117,10 @@ static unsigned int features[] = {
>>  	VIRTIO_BALLOON_F_MUST_TELL_HOST,
>>  	VIRTIO_BALLOON_F_STATS_VQ,
>>  	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
>> +	VIRTIO_BALLOON_F_HINTING,
>>  	VIRTIO_BALLOON_F_FREE_PAGE_HINT,
>>  	VIRTIO_BALLOON_F_PAGE_POISON,
>> +	VIRTIO_BALLOON_F_HINTING,
>>  };
>>  
>>  static struct virtio_driver virtio_balloon_driver = {
>> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
>> index a1966cd7b677..29eed0ec83d3 100644
>> --- a/include/uapi/linux/virtio_balloon.h
>> +++ b/include/uapi/linux/virtio_balloon.h
>> @@ -36,6 +36,8 @@
>>  #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 */
>> +/* TODO: Find a better name to avoid any confusion with FREE_PAGE_HINT */
>> +#define VIRTIO_BALLOON_F_HINTING	5 /* Page hinting virtqueue */
>>  
>>  /* Size of a PFN in the balloon interface. */
>>  #define VIRTIO_BALLOON_PFN_SHIFT 12
>> @@ -108,4 +110,13 @@ struct virtio_balloon_stat {
>>  	__virtio64 val;
>>  } __attribute__((packed));
>>  
>> +/*
>> + * struct isolated_memory- holds the pages which will be reported to the host.
>> + * @phys_add:	physical address associated with a page.
>> + * @size:	total size of memory to be reported.
>> + */
>> +struct isolated_memory {
>> +	__virtio64 phys_addr;
>> +	__virtio64 size;
>> +};
>>  #endif /* _LINUX_VIRTIO_BALLOON_H */
>> -- 
>> 2.21.0
-- 
Thanks
Nitesh