Re: [PATCH v2 1/2] balloon: introduce 6 memory statistics

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

On Thu, Jun 06, 2024 at 11:35:43AM +0800, zhenwei pi wrote:
> Note that virtio balloon statistics are OS independent, the names are
> not completely the same as Linux or Windows. For example, 'reclaim' is
> more general than 'steal' (on linux) and 'repurpose' (on windows) for
> a modern operating system.
> 
> Expose more memory statistics of the virtual memory subsystem from
> guest, it's helpful to analyze the memory performance and pressure
> from host side.
> 
> More, once the memory pressure gets critical, a task hits ALLOC STALL,
> and reclaims pages in batch directly. So the ALLOC STALL count is not
> the same as direct reclaim count.
> 
> Now we have a metric to analyze the memory performance:
> - y: counter increases
> - n: counter does not changes
> - h: the rate of counter change is high
> - l: the rate of counter change is low
> 
> OOM: VIRTIO_BALLOON_S_OOM_KILL
> STALL: VIRTIO_BALLOON_S_ALLOC_STALL
> ASCAN: VIRTIO_BALLOON_S_SCAN_ASYNC
> DSCAN: VIRTIO_BALLOON_S_SCAN_DIRECT
> ARCLM: VIRTIO_BALLOON_S_RECLAIM_ASYNC
> DRCLM: VIRTIO_BALLOON_S_RECLAIM_DIRECT
> 
> - OOM[y], STALL[*], ASCAN[*], DSCAN[*], ARCLM[*], DRCLM[*]:
>   the guest runs under really critial memory pressure
> 
> - OOM[n], STALL[h], ASCAN[*], DSCAN[l], ARCLM[*], DRCLM[l]:
>   the memory allocation stalls due to cgroup, not the global memory
>   pressure (for Linux).
> 
> - OOM[n], STALL[h], ASCAN[*], DSCAN[h], ARCLM[*], DRCLM[h]:
>   the memory allocation stalls due to global memory pressure. The
>   performance gets hurt a lot. A high ratio between DRCLM/DSCAN shows
>   quite effective memory reclaiming.
> 
> - OOM[n], STALL[h], ASCAN[*], DSCAN[h], ARCLM[*], DRCLM[l]:
>   the memory allocation stalls due to global memory pressure.
>   the ratio between DRCLM/DSCAN gets low, the guest OS is thrashing
>   heavily, the serious case leads poor performance and difficult
>   trouble shooting. Ex, sshd may block on memory allocation when
>   accepting new connections, a user can't login a VM by ssh command.
> 
> - OOM[n], STALL[n], ASCAN[h], DSCAN[n], ARCLM[l], DRCLM[n]:
>   the low ratio between ARCLM/ASCAN shows that the guest tries to
>   reclaim more memory, but it can't. Once more memory is required in
>   future, it will struggle to reclaim memory.
> 
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  device-types/balloon/description.tex | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/device-types/balloon/description.tex b/device-types/balloon/description.tex
> index a1d9603..7ef4e3f 100644
> --- a/device-types/balloon/description.tex
> +++ b/device-types/balloon/description.tex
> @@ -305,6 +305,12 @@ \subsubsection{Memory Statistics}\label{sec:Device Types / Memory Balloon Device
>  #define VIRTIO_BALLOON_S_CACHES   7
>  #define VIRTIO_BALLOON_S_HTLB_PGALLOC 8
>  #define VIRTIO_BALLOON_S_HTLB_PGFAIL  9
> +#define VIRTIO_BALLOON_S_OOM_KILL       10
> +#define VIRTIO_BALLOON_S_ALLOC_STALL    11
> +#define VIRTIO_BALLOON_S_ASYNC_SCAN     12
> +#define VIRTIO_BALLOON_S_DIRECT_SCAN    13
> +#define VIRTIO_BALLOON_S_ASYNC_RECLAIM  14
> +#define VIRTIO_BALLOON_S_DIRECT_RECLAIM 15
>          le16 tag;
>          le64 val;
>  } __attribute__((packed));
> @@ -399,6 +405,24 @@ \subsubsection{Memory Statistics Tags}\label{sec:Device Types / Memory Balloon D
>  
>  \item[VIRTIO_BALLOON_S_HTLB_PGFAIL (9)] The number of failed hugetlb page
>    allocations in the guest.
> +
> +\item[VIRTIO_BALLOON_S_OOM_KILL (10)] The count of OOM killer invocations
> +  increases when the kernel invokes the OOM killer. The OOM killer selects a task
> +  to terminate in order to free up memory.
> +
> +\item[VIRTIO_BALLOON_S_ALLOC_STALL (11)] The count of stalls on memory allocation.
> +
> +\item[VIRTIO_BALLOON_S_ASYNC_SCAN (12)] The amount of memory scanned asynchronously
> +  by the kernel background task (in bytes).
> +
> +\item[VIRTIO_BALLOON_S_DIRECT_SCAN (13)] The amount of memory scanned directly by
> +  the running task (in bytes).
> +
> +\item[VIRTIO_BALLOON_S_ASYNC_RECLAIM (14)] The amount of memory reclaimed
> +  asynchronously by the kernel background task (in bytes).
> +
> +\item[VIRTIO_BALLOON_S_DIRECT_RECLAIM (15)] The amount of memory reclaimed
> +  directly by the running task (in bytes).
>  \end{description}

OOM kill description is unnecessarily verbose, the rest not very clear,
and not consistent with existing stats.


>  \subsubsection{Free Page Hinting}\label{sec:Device Types / Memory Balloon Device / Device Operation / Free Page Hinting}
> -- 
> 2.43.0
>