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From: zhenwei pi <pizhenwei@bytedance.com>
To: linux-kernel@vger.kernel.org,
	linux-mm@kvack.org,
	virtualization@lists.linux.dev
Cc: mst@redhat.com,
	david@redhat.com,
	jasowang@redhat.com,
	xuanzhuo@linux.alibaba.com,
	akpm@linux-foundation.org,
	zhenwei pi <pizhenwei@bytedance.com>
Subject: [RFC 3/3] virtio_balloon: introduce memory scan/reclaim info
Date: Mon, 15 Apr 2024 16:41:13 +0800
Message-Id: <20240415084113.1203428-4-pizhenwei@bytedance.com>
In-Reply-To: <20240415084113.1203428-1-pizhenwei@bytedance.com>
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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 */
+#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" \
 }
 
 #define VIRTIO_BALLOON_S_NAMES VIRTIO_BALLOON_S_NAMES_WITH_PREFIX("")
-- 
2.34.1