[Qemu-devel] virtio: Report new guest memory statistics pertinent to memory ballooning (V3)

[Adam Litke <agl@us.ibm.com>]

virtio: Report new guest memory statistics pertinent to memory ballooning (V3)

Changes since V2:
 - Use a virtqueue for communication instead of the device config space

Changes since V1:
 - In the monitor, print all stats on one line with less abbreviated names
 - Coding style changes

When using ballooning to manage overcommitted memory on a host, a system for
guests to communicate their memory usage to the host can provide information
that will minimize the impact of ballooning on the guests.  The current method
employs a daemon running in each guest that communicates memory statistics to a
host daemon at a specified time interval.  The host daemon aggregates this
information and inflates and/or deflates balloons according to the level of
host memory pressure.  This approach is effective but overly complex since a
daemon must be installed inside each guest and coordinated to communicate with
the host.  A simpler approach is to collect memory statistics in the virtio
balloon driver and communicate them directly to the hypervisor.

This patch implements the qemu side of the communication channel.  I will post
the kernel driver modifications in-reply to this message.

Signed-off-by: Adam Litke <agl@us.ibm.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: qemu-devel@nongnu.org

diff --git a/balloon.h b/balloon.h
index 60b4a5d..def4c56 100644
--- a/balloon.h
+++ b/balloon.h
@@ -16,12 +16,12 @@
 
 #include "cpu-defs.h"
 
-typedef ram_addr_t (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
+typedef int (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
 
 void qemu_add_balloon_handler(QEMUBalloonEvent *func, void *opaque);
 
 void qemu_balloon(ram_addr_t target);
 
-ram_addr_t qemu_balloon_status(void);
+int qemu_balloon_status(void);
 
 #endif
diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index cfd3b41..81dd1f3 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -19,6 +19,7 @@
 #include "balloon.h"
 #include "virtio-balloon.h"
 #include "kvm.h"
+#include "monitor.h"
 
 #if defined(__linux__)
 #include <sys/mman.h>
@@ -27,9 +28,13 @@
 typedef struct VirtIOBalloon
 {
     VirtIODevice vdev;
-    VirtQueue *ivq, *dvq;
+    VirtQueue *ivq, *dvq, *svq;
     uint32_t num_pages;
     uint32_t actual;
+    uint32_t stats[VIRTIO_BALLOON_S_NR];
+    VirtQueueElement stats_vq_elem;
+    size_t stats_vq_offset;
+    uint8_t stats_requested;
 } VirtIOBalloon;
 
 static VirtIOBalloon *to_virtio_balloon(VirtIODevice *vdev)
@@ -46,6 +51,34 @@ static void balloon_page(void *addr, int deflate)
 #endif
 }
 
+static inline void reset_stats(VirtIOBalloon *dev)
+{
+    int i;
+    for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
+}
+
+static inline void print_stat(uint32_t val, const char *label)
+{
+    if (val != -1) {
+        monitor_printf(cur_mon, ",%s=%u", label, val);
+    }
+}
+
+static void virtio_balloon_print_stats(VirtIOBalloon *dev)
+{
+    uint32_t actual = ram_size - (dev->actual << VIRTIO_BALLOON_PFN_SHIFT);
+
+    monitor_printf(cur_mon, "balloon: actual=%d", (int)(actual >> 20));
+    print_stat(dev->stats[VIRTIO_BALLOON_S_SWAP_IN], "pages_swapped_in");
+    print_stat(dev->stats[VIRTIO_BALLOON_S_SWAP_OUT], "pages_swapped_out");
+    print_stat(dev->stats[VIRTIO_BALLOON_S_ANON], "anon_pages");
+    print_stat(dev->stats[VIRTIO_BALLOON_S_MAJFLT], "major_page_faults");
+    print_stat(dev->stats[VIRTIO_BALLOON_S_MINFLT], "minor_page_faults");
+    print_stat(dev->stats[VIRTIO_BALLOON_S_MEMFREE], "free_memory");
+    print_stat(dev->stats[VIRTIO_BALLOON_S_MEMTOT], "total_memory");
+    monitor_printf(cur_mon, "\n");
+}
+
 /* FIXME: once we do a virtio refactoring, this will get subsumed into common
  * code */
 static size_t memcpy_from_iovector(void *data, size_t offset, size_t size,
@@ -104,6 +137,31 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
     }
 }
 
+static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *s = to_virtio_balloon(vdev);
+    VirtQueueElement *elem = &s->stats_vq_elem;
+    VirtIOBalloonStat stat;
+    size_t offset = 0;
+
+    if (!virtqueue_pop(vq, elem))
+        return;
+
+    while (memcpy_from_iovector(&stat, offset, sizeof(stat), elem->out_sg,
+                                elem->out_num) == sizeof(stat)) {
+        offset += sizeof(stat);
+        if (stat.tag < VIRTIO_BALLOON_S_NR)
+            s->stats[stat.tag] = stat.val;
+    }
+    s->stats_vq_offset = offset;
+
+    if (s->stats_requested) {
+        virtio_balloon_print_stats(s);
+        monitor_resume(cur_mon);
+        s->stats_requested = 0;
+    }
+}
+
 static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
 {
     VirtIOBalloon *dev = to_virtio_balloon(vdev);
@@ -126,10 +184,19 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
 
 static uint32_t virtio_balloon_get_features(VirtIODevice *vdev)
 {
-    return 0;
+    return 1 << VIRTIO_BALLOON_F_STATS_VQ;
 }
 
-static ram_addr_t virtio_balloon_to_target(void *opaque, ram_addr_t target)
+static void request_stats(VirtIOBalloon *vb)
+{
+    vb->stats_requested = 1;
+    reset_stats(vb);
+    monitor_suspend(cur_mon);
+    virtqueue_push(vb->svq, &vb->stats_vq_elem, vb->stats_vq_offset);
+    virtio_notify(&vb->vdev, vb->svq);
+}
+
+static int virtio_balloon_to_target(void *opaque, ram_addr_t target)
 {
     VirtIOBalloon *dev = opaque;
 
@@ -139,9 +206,14 @@ static ram_addr_t virtio_balloon_to_target(void *opaque, ram_addr_t target)
     if (target) {
         dev->num_pages = (ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
         virtio_notify_config(&dev->vdev);
+    } else if (dev->vdev.features & (1 << VIRTIO_BALLOON_F_STATS_VQ)) {
+        request_stats(dev);
+    } else {
+        reset_stats(dev);
+        virtio_balloon_print_stats(dev);
     }
 
-    return ram_size - (dev->actual << VIRTIO_BALLOON_PFN_SHIFT);
+    return 0;
 }
 
 static void virtio_balloon_save(QEMUFile *f, void *opaque)
@@ -152,6 +224,9 @@ static void virtio_balloon_save(QEMUFile *f, void *opaque)
 
     qemu_put_be32(f, s->num_pages);
     qemu_put_be32(f, s->actual);
+    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_elem, sizeof(VirtQueueElement));
+    qemu_put_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
+    qemu_put_byte(f, s->stats_requested);
 }
 
 static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
@@ -165,6 +240,9 @@ static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
 
     s->num_pages = qemu_get_be32(f);
     s->actual = qemu_get_be32(f);
+    qemu_get_buffer(f, (uint8_t *)&s->stats_vq_elem, sizeof(VirtQueueElement));
+    qemu_get_buffer(f, (uint8_t *)&s->stats_vq_offset, sizeof(size_t));
+    s->stats_requested = qemu_get_byte(f);
 
     return 0;
 }
@@ -183,6 +261,7 @@ VirtIODevice *virtio_balloon_init(DeviceState *dev)
 
     s->ivq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
     s->dvq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
+    s->svq = virtio_add_queue(&s->vdev, 128, virtio_balloon_receive_stats);
 
     qemu_add_balloon_handler(virtio_balloon_to_target, s);
 
diff --git a/hw/virtio-balloon.h b/hw/virtio-balloon.h
index 9a0d119..005ddeb 100644
--- a/hw/virtio-balloon.h
+++ b/hw/virtio-balloon.h
@@ -25,6 +25,7 @@
 
 /* The feature bitmap for virtio balloon */
 #define VIRTIO_BALLOON_F_MUST_TELL_HOST 0 /* Tell before reclaiming pages */
+#define VIRTIO_BALLOON_F_STATS_VQ 1       /* Memory stats virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
@@ -37,4 +38,19 @@ struct virtio_balloon_config
     uint32_t actual;
 };
 
+/* Memory Statistics */
+#define VIRTIO_BALLOON_S_SWAP_IN  0   /* Number of pages swapped in */
+#define VIRTIO_BALLOON_S_SWAP_OUT 1   /* Number of pages swapped out */
+#define VIRTIO_BALLOON_S_ANON     2   /* Number of anonymous pages in use */
+#define VIRTIO_BALLOON_S_MAJFLT   3   /* Number of major faults */
+#define VIRTIO_BALLOON_S_MINFLT   4   /* Number of minor faults */
+#define VIRTIO_BALLOON_S_MEMFREE  5   /* Total amount of free memory */
+#define VIRTIO_BALLOON_S_MEMTOT   6   /* Total amount of memory */
+#define VIRTIO_BALLOON_S_NR       7
+
+typedef struct VirtIOBalloonStat {
+    uint16_t tag;
+    uint32_t val;
+} VirtIOBalloonStat;
+
 #endif
diff --git a/monitor.c b/monitor.c
index ed1ce6e..73484c8 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1583,16 +1583,14 @@ static void do_balloon(Monitor *mon, int value)
 
 static void do_info_balloon(Monitor *mon)
 {
-    ram_addr_t actual;
+    int ret;
 
-    actual = qemu_balloon_status();
     if (kvm_enabled() && !kvm_has_sync_mmu())
         monitor_printf(mon, "Using KVM without synchronous MMU, "
                        "ballooning disabled\n");
-    else if (actual == 0)
+    ret = qemu_balloon_status();
+    if (ret == -1)
         monitor_printf(mon, "Ballooning not activated in VM\n");
-    else
-        monitor_printf(mon, "balloon: actual=%d\n", (int)(actual >> 20));
 }
 
 static qemu_acl *find_acl(Monitor *mon, const char *name)
diff --git a/vl.c b/vl.c
index 710d52e..aebceab 100644
--- a/vl.c
+++ b/vl.c
@@ -337,11 +337,11 @@ void qemu_balloon(ram_addr_t target)
         qemu_balloon_event(qemu_balloon_event_opaque, target);
 }
 
-ram_addr_t qemu_balloon_status(void)
+int qemu_balloon_status(void)
 {
     if (qemu_balloon_event)
         return qemu_balloon_event(qemu_balloon_event_opaque, 0);
-    return 0;
+    return -1;
 }
 
 /***********************************************************/


-- 
Thanks,
Adam