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

[David Hildenbrand]

On 24.07.19 21:47, 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@xxxxxxxxxx>
>> ---
>>  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.
> 

+1

I especially like passing full addresses and sizes instead of PFNs and
orders (compared to Alex's v1, where he would pass PFNs and orders).

-- 

Thanks,

David / dhildenb