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Date: Mon, 15 Apr 2024 17:06:20 +0200
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Subject: Re: [RFC 3/3] virtio_balloon: introduce memory scan/reclaim info
To: zhenwei pi <pizhenwei@bytedance.com>, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org, virtualization@lists.linux.dev
Cc: mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com,
 akpm@linux-foundation.org
References: <20240415084113.1203428-1-pizhenwei@bytedance.com>
 <20240415084113.1203428-4-pizhenwei@bytedance.com>
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From: David Hildenbrand <david@redhat.com>
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In-Reply-To: <20240415084113.1203428-4-pizhenwei@bytedance.com>
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On 15.04.24 10:41, zhenwei pi wrote:
> Expose memory scan/reclaim information to the host side via virtio
> balloon device.
> 
> 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.
> 
> - 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>
> ---
>   drivers/virtio/virtio_balloon.c     |  9 +++++++++
>   include/uapi/linux/virtio_balloon.h | 12 ++++++++++--
>   2 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 4b9c9569f6e5..7b86514e99d4 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -372,6 +372,15 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb)
>   	stall += events[ALLOCSTALL_MOVABLE];
>   	update_stat(vb, idx++, VIRTIO_BALLOON_S_ALLOC_STALL, stall);
>   
> +	update_stat(vb, idx++, VIRTIO_BALLOON_S_SCAN_ASYNC,
> +				pages_to_bytes(events[PGSCAN_KSWAPD]));
> +	update_stat(vb, idx++, VIRTIO_BALLOON_S_SCAN_DIRECT,
> +				pages_to_bytes(events[PGSCAN_DIRECT]));
> +	update_stat(vb, idx++, VIRTIO_BALLOON_S_RECLAIM_ASYNC,
> +				pages_to_bytes(events[PGSTEAL_KSWAPD]));
> +	update_stat(vb, idx++, VIRTIO_BALLOON_S_RECLAIM_DIRECT,
> +				pages_to_bytes(events[PGSTEAL_DIRECT]));
> +
>   	return idx;
>   }
>   
> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
> index 13d0c32ba27c..0875a9cccb01 100644
> --- a/include/uapi/linux/virtio_balloon.h
> +++ b/include/uapi/linux/virtio_balloon.h
> @@ -73,7 +73,11 @@ struct virtio_balloon_config {
>   #define VIRTIO_BALLOON_S_HTLB_PGFAIL   9  /* Hugetlb page allocation failures */
>   #define VIRTIO_BALLOON_S_OOM_KILL      10 /* OOM killer invocations */
>   #define VIRTIO_BALLOON_S_ALLOC_STALL   11 /* Stall count of memory allocatoin */
> -#define VIRTIO_BALLOON_S_NR       12
> +#define VIRTIO_BALLOON_S_SCAN_ASYNC    12 /* Amount of memory scanned asynchronously */
> +#define VIRTIO_BALLOON_S_SCAN_DIRECT   13 /* Amount of memory scanned directly */
> +#define VIRTIO_BALLOON_S_RECLAIM_ASYNC 14 /* Amount of memory reclaimed asynchronously */
> +#define VIRTIO_BALLOON_S_RECLAIM_DIRECT 15 /* Amount of memory reclaimed directly */

Should these be the other way around:

ASYN_SCAN
..
ASYNC_RECLAIM

so we can get ...

> +#define VIRTIO_BALLOON_S_NR       16
>   
>   #define VIRTIO_BALLOON_S_NAMES_WITH_PREFIX(VIRTIO_BALLOON_S_NAMES_prefix) { \
>   	VIRTIO_BALLOON_S_NAMES_prefix "swap-in", \
> @@ -87,7 +91,11 @@ struct virtio_balloon_config {
>   	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-allocations", \
>   	VIRTIO_BALLOON_S_NAMES_prefix "hugetlb-failures", \
>   	VIRTIO_BALLOON_S_NAMES_prefix "oom-kill", \
> -	VIRTIO_BALLOON_S_NAMES_prefix "alloc-stall" \
> +	VIRTIO_BALLOON_S_NAMES_prefix "alloc-stall", \
> +	VIRTIO_BALLOON_S_NAMES_prefix "scan-async", \
> +	VIRTIO_BALLOON_S_NAMES_prefix "scan-direct", \
> +	VIRTIO_BALLOON_S_NAMES_prefix "reclaim-async", \
> +	VIRTIO_BALLOON_S_NAMES_prefix "reclaim-direct" \

..

"async-scans", "async-reclaims" ...

-- 
Cheers,

David / dhildenb