Linux Virtualization - Feb 2016 - [PATCH 2/2] virtio_balloon: export 'available' memory to balloon statistics

On Tue, Feb 16, 2016 at 06:50:52PM +0300, Denis V. Lunev
wrote:
> From: Igor Redko <redkoi at 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 at virtuozzo.com>
> Reviewed-by: Roman Kagan <rkagan at virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den at openvz.org>
> CC: Michael S. Tsirkin <mst at redhat.com>
> CC: Andrew Morton <akpm at 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

On 02/23/2016 06:10 PM, Michael S. Tsirkin wrote:
> On Tue, Feb 16, 2016 at 06:50:52PM +0300, Denis V. Lunev wrote:
>> From: Igor Redko <redkoi at 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 at virtuozzo.com>
>> Reviewed-by: Roman Kagan <rkagan at virtuozzo.com>
>> Signed-off-by: Denis V. Lunev <den at openvz.org>
>> CC: Michael S. Tsirkin <mst at redhat.com>
>> CC: Andrew Morton <akpm at 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.
hmmm

 From my point of view ABI remains untouched.
The guest can send any amount of <tag>;<value>
pairs and unknown tags are properly ignored
by the host.

That is why I think that this change is safe.

On Tue, Feb 23, 2016 at 06:26:47PM +0300, Denis V. Lunev
wrote:
> On 02/23/2016 06:10 PM, Michael S. Tsirkin wrote:
> >On Tue, Feb 16, 2016 at 06:50:52PM +0300, Denis V. Lunev wrote:
> >>From: Igor Redko <redkoi at 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 at virtuozzo.com>
> >>Reviewed-by: Roman Kagan <rkagan at virtuozzo.com>
> >>Signed-off-by: Denis V. Lunev <den at openvz.org>
> >>CC: Michael S. Tsirkin <mst at redhat.com>
> >>CC: Andrew Morton <akpm at 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.
> 
> hmmm
> 
> From my point of view ABI remains untouched.
Anything exposed by guest to host is ABI.
Once we add stuff there, we never can remove it
as some host might rely on it.
> The guest can send any amount of <tag>;<value>
> pairs and unknown tags are properly ignored
> by the host.
> 
> That is why I think that this change is safe.
What happens if someone uses the tag you
used for VIRTIO_BALLOON_S_AVAIL, for some
other purpose?
Any tools using VIRTIO_BALLOON_S_AVAIL will be confused.

Really, it's not hard to get a tag number from virtio TC,
so please just do this.

-- 
MST