virtio_balloon: introduce memory allocation stall counter

Memory allocation stall counter represents the performance/latency of
memory allocation, expose this counter to the host side by virtio
balloon device via out-of-bound way.

Acked-by: David Hildenbrand <[e-mail]>
Signed-off-by: zhenwei pi <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>

drivers/virtio/virtio_balloon.c

···
 {
 	unsigned long events[NR_VM_EVENT_ITEMS];
 	unsigned int idx = 0;
+	unsigned int zid;
+	unsigned long stall = 0;
 
 	all_vm_events(events);
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
···
 	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]);
+
+	/* sum all the stall events */
+	for (zid = 0; zid < MAX_NR_ZONES; zid++)
+		stall += events[ALLOCSTALL_NORMAL - ZONE_NORMAL + zid];
+
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_ALLOC_STALL, stall);
 
 #ifdef CONFIG_HUGETLB_PAGE
 	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,

include/uapi/linux/virtio_balloon.h

···
 #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_OOM_KILL      10 /* OOM killer invocations */
-#define VIRTIO_BALLOON_S_NR       11
+#define VIRTIO_BALLOON_S_ALLOC_STALL   11 /* Stall count of memory allocatoin */
+#define VIRTIO_BALLOON_S_NR       12
 
 #define VIRTIO_BALLOON_S_NAMES_WITH_PREFIX(VIRTIO_BALLOON_S_NAMES_prefix) { \
 	VIRTIO_BALLOON_S_NAMES_prefix "swap-in", \
···
 	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 "oom-kills" \
+	VIRTIO_BALLOON_S_NAMES_prefix "oom-kills", \
+	VIRTIO_BALLOON_S_NAMES_prefix "alloc-stalls" \
 }
 
 #define VIRTIO_BALLOON_S_NAMES VIRTIO_BALLOON_S_NAMES_WITH_PREFIX("")