Re: [PATCH v3 2/4] virtio_balloon: introduce oom-kill invocations

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

On Tue, Apr 23, 2024 at 11:41:07AM +0800, zhenwei pi wrote:
> When the guest OS runs under critical memory pressure, the guest
> starts to kill processes. A guest monitor agent may scan 'oom_kill'
> from /proc/vmstat, and reports the OOM KILL event. However, the agent
> may be killed and we will loss this critical event(and the later
> events).
> 
> For now we can also grep for magic words in guest kernel log from host
> side. Rather than this unstable way, virtio balloon reports OOM-KILL
> invocations instead.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  drivers/virtio/virtio_balloon.c     | 1 +
>  include/uapi/linux/virtio_balloon.h | 6 ++++--
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 1710e3098ecd..f7a47eaa0936 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -330,6 +330,7 @@ static inline unsigned int update_balloon_vm_stats(struct virtio_balloon *vb)
>  		    pages_to_bytes(events[PSWPOUT]));
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
> +	update_stat(vb, idx++, VIRTIO_BALLOON_S_OOM_KILL, events[OOM_KILL]);
>  
>  #ifdef CONFIG_HUGETLB_PAGE
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index ddaa45e723c4..b17bbe033697 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -71,7 +71,8 @@ struct virtio_balloon_config {
>  #define VIRTIO_BALLOON_S_CACHES   7   /* Disk caches */
>  #define VIRTIO_BALLOON_S_HTLB_PGALLOC  8  /* Hugetlb page allocations */
>  #define VIRTIO_BALLOON_S_HTLB_PGFAIL   9  /* Hugetlb page allocation failures */
> -#define VIRTIO_BALLOON_S_NR       10
> +#define VIRTIO_BALLOON_S_OOM_KILL      10 /* OOM killer invocations */
> +#define VIRTIO_BALLOON_S_NR       11
>  
>  #define VIRTIO_BALLOON_S_NAMES_WITH_PREFIX(VIRTIO_BALLOON_S_NAMES_prefix) { \
>  	VIRTIO_BALLOON_S_NAMES_prefix "swap-in", \

Looks like a useful extension. But
any UAPI extension has to go to virtio spec first.

> @@ -83,7 +84,8 @@ struct virtio_balloon_config {
>  	VIRTIO_BALLOON_S_NAMES_prefix "available-memory", \
>  	VIRTIO_BALLOON_S_NAMES_prefix "disk-caches", \
>  	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-allocations", \
> -	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-failures" \
> +	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-failures", \
> +	VIRTIO_BALLOON_S_NAMES_prefix "oom-kills" \
>  }
>  
>  #define VIRTIO_BALLOON_S_NAMES VIRTIO_BALLOON_S_NAMES_WITH_PREFIX("")
> -- 
> 2.34.1