Re: [PATCH 2/2] virtio_balloon: export 'available' memory to balloon statistics

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Feb 16, 2016 at 06:50:52PM +0300, Denis V. Lunev wrote:
> From: Igor Redko <redkoi@virtuozzo.com>
> 
> Add a new field, VIRTIO_BALLOON_S_AVAIL, to virtio_balloon memory
> statistics protocol, corresponding to 'Available' in /proc/meminfo.
> 
> It indicates to the hypervisor how big the balloon can be inflated
> without pushing the guest system to swap.
> 
> Signed-off-by: Igor Redko <redkoi@virtuozzo.com>
> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Michael S. Tsirkin <mst@redhat.com>
> CC: Andrew Morton <akpm@linux-foundation.org>

Oops - I missed the fact that this affects host/guest ABI.

Can you please submit ABI update proposal to virtio tc?
Spec patch would be even better.

This is important to ensure there are no conflicts
with other features being developed in parallel.

> ---
>  drivers/virtio/virtio_balloon.c     | 6 ++++++
>  include/uapi/linux/virtio_balloon.h | 3 ++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 0c3691f..f2b77de 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -30,6 +30,7 @@
>  #include <linux/balloon_compaction.h>
>  #include <linux/oom.h>
>  #include <linux/wait.h>
> +#include <linux/mm.h>
>  
>  /*
>   * Balloon device works in 4K page units.  So each page is pointed to by
> @@ -229,10 +230,13 @@ static void update_balloon_stats(struct virtio_balloon *vb)
>  	unsigned long events[NR_VM_EVENT_ITEMS];
>  	struct sysinfo i;
>  	int idx = 0;
> +	long available;
>  
>  	all_vm_events(events);
>  	si_meminfo(&i);
>  
> +	available = si_mem_available();
> +
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
>  				pages_to_bytes(events[PSWPIN]));
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
> @@ -243,6 +247,8 @@ static void update_balloon_stats(struct virtio_balloon *vb)
>  				pages_to_bytes(i.freeram));
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
>  				pages_to_bytes(i.totalram));
> +	update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
> +				pages_to_bytes(available));
>  }
>  
>  /*
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index d7f1cbc..343d7dd 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -51,7 +51,8 @@ struct virtio_balloon_config {
>  #define VIRTIO_BALLOON_S_MINFLT   3   /* Number of minor faults */
>  #define VIRTIO_BALLOON_S_MEMFREE  4   /* Total amount of free memory */
>  #define VIRTIO_BALLOON_S_MEMTOT   5   /* Total amount of memory */
> -#define VIRTIO_BALLOON_S_NR       6
> +#define VIRTIO_BALLOON_S_AVAIL    6   /* Available memory as in /proc */
> +#define VIRTIO_BALLOON_S_NR       7
>  
>  /*
>   * Memory statistics structure.
> -- 
> 2.5.0