Re: [Qemu-devel] [PATCH v2 1/1] virtio_balloon: include buffers and cached memory statistics

[Michael S. Tsirkin]

On Thu, Sep 21, 2017 at 02:55:41PM +0200, Tomáš Golembiovský wrote:
> Add a new fields, VIRTIO_BALLOON_S_BUFFERS and VIRTIO_BALLOON_S_CACHED,
> to virtio_balloon memory statistics protocol. The values correspond to
> 'Buffers' and 'Cached' in /proc/meminfo.
> 
> To be able to compute the value of 'Cached' memory it is necessary to
> export total_swapcache_pages() to modules.
> 
> Signed-off-by: Tomáš Golembiovský <address@hidden>

Does 'Buffers' actually make sense? It's a temporary storage -
wouldn't it be significantly out of date by the time
host receives it?

> ---
>  drivers/virtio/virtio_balloon.c     | 11 +++++++++++
>  include/uapi/linux/virtio_balloon.h |  4 +++-
>  mm/swap_state.c                     |  1 +
>  3 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index f0b3a0b9d42f..c2558ec47a62 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -244,12 +244,19 @@ static unsigned int update_balloon_stats(struct 
> virtio_balloon *vb)
>       struct sysinfo i;
>       unsigned int idx = 0;
>       long available;
> +     long cached;
>  
>       all_vm_events(events);
>       si_meminfo(&i);
>  
>       available = si_mem_available();
>  
> +     cached = global_node_page_state(NR_FILE_PAGES) -
> +                     total_swapcache_pages() - i.bufferram;
> +     if (cached < 0)
> +             cached = 0;
> +
> +
>  #ifdef CONFIG_VM_EVENT_COUNTERS
>       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
>                               pages_to_bytes(events[PSWPIN]));
> @@ -264,6 +271,10 @@ static unsigned int update_balloon_stats(struct 
> virtio_balloon *vb)
>                               pages_to_bytes(i.totalram));
>       update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
>                               pages_to_bytes(available));
> +     update_stat(vb, idx++, VIRTIO_BALLOON_S_BUFFERS,
> +                             pages_to_bytes(i.bufferram));
> +     update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHED,
> +                             pages_to_bytes(cached));
>  
>       return idx;
>  }
> diff --git a/include/uapi/linux/virtio_balloon.h 
> b/include/uapi/linux/virtio_balloon.h
> index 343d7ddefe04..d5dc8a56a497 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -52,7 +52,9 @@ struct virtio_balloon_config {
>  #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_AVAIL    6   /* Available memory as in /proc */
> -#define VIRTIO_BALLOON_S_NR       7
> +#define VIRTIO_BALLOON_S_BUFFERS  7   /* Buffers memory as in /proc */
> +#define VIRTIO_BALLOON_S_CACHED   8   /* Cached memory as in /proc */
> +#define VIRTIO_BALLOON_S_NR       9
>  
>  /*
>   * Memory statistics structure.
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 71ce2d1ccbf7..f3a4ff7d6c52 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -95,6 +95,7 @@ unsigned long total_swapcache_pages(void)
>       rcu_read_unlock();
>       return ret;
>  }
> +EXPORT_SYMBOL_GPL(total_swapcache_pages);
>  
>  static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);

Need an ack from MM crowd on that.

> -- 
> 2.14.1