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Re: [Qemu-devel] virtio: Add memory statistics reporting to the balloon


From: Anthony Liguori
Subject: Re: [Qemu-devel] virtio: Add memory statistics reporting to the balloon driver (V8)
Date: Tue, 26 Jan 2010 18:08:02 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091209 Fedora/3.0-4.fc12 Lightning/1.0pre Thunderbird/3.0

On 01/26/2010 02:17 PM, Adam Litke wrote:
The changes in V8 of this patch are related to the monitor infrastructure.  No
changes to the virtio interface core have been made since V4.  This is intended
to apply on top of my API for asynchronous monitor commands patch.

Changes since V7:
  - Ported to the asynchronous monitor API

Changes since V6:
  - Integrated with virtio qdev feature bit changes
    (specifically: Use VirtIODevice 'guest_features' to check if memory stats
    is a negotiated feature)
  - Track which monitor initiated the most recent stats request.  Now it does 
the
    Right Thing(tm) with multiple monitors making parallel requests.

Changes since V5:
  - Asynchronous query-balloon mode for QMP
  - Add timeout to prevent hanging the user monitor in synchronous mode

Changes since V4:
  - Virtio spec updated: 
http://ozlabs.org/~rusty/virtio-spec/virtio-spec-0.8.2.pdf
  - Guest-side Linux implementation applied by Rusty
  - Start using the QObject infrastructure
  - All endian conversions done in the host
  - Report stats that reference a quantity of memory in bytes

Changes since V3:
  - Increase stat field size to 64 bits
  - Report all sizes in kb (not pages)
  - Drop anon_pages stat

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.

Signed-off-by: Adam Litke<address@hidden>
To: Anthony Liguori<address@hidden>
Cc: Avi Kivity<address@hidden>
Cc: Luiz Capitulino<address@hidden>
Cc: address@hidden

Applied.  Thanks.

Regards,

Anthony Liguori
diff --git a/balloon.h b/balloon.h
index 60b4a5d..c3a1ad3 100644
--- a/balloon.h
+++ b/balloon.h
@@ -16,12 +16,13 @@

  #include "cpu-defs.h"

-typedef ram_addr_t (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
+typedef void (QEMUBalloonEvent)(void *opaque, ram_addr_t target,
+                                MonitorCompletion cb, void *cb_data);

  void qemu_add_balloon_handler(QEMUBalloonEvent *func, void *opaque);

-void qemu_balloon(ram_addr_t target);
+int qemu_balloon(ram_addr_t target, MonitorCompletion cb, void *opaque);

-ram_addr_t qemu_balloon_status(void);
+int qemu_balloon_status(MonitorCompletion cb, void *opaque);

  #endif
diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index e17880f..086d9d1 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -16,9 +16,13 @@
  #include "pc.h"
  #include "sysemu.h"
  #include "cpu.h"
+#include "monitor.h"
  #include "balloon.h"
  #include "virtio-balloon.h"
  #include "kvm.h"
+#include "qlist.h"
+#include "qint.h"
+#include "qstring.h"

  #if defined(__linux__)
  #include<sys/mman.h>
@@ -27,9 +31,14 @@
  typedef struct VirtIOBalloon
  {
      VirtIODevice vdev;
-    VirtQueue *ivq, *dvq;
+    VirtQueue *ivq, *dvq, *svq;
      uint32_t num_pages;
      uint32_t actual;
+    uint64_t stats[VIRTIO_BALLOON_S_NR];
+    VirtQueueElement stats_vq_elem;
+    size_t stats_vq_offset;
+    MonitorCompletion *stats_callback;
+    void *stats_opaque_callback_data;
  } VirtIOBalloon;

  static VirtIOBalloon *to_virtio_balloon(VirtIODevice *vdev)
@@ -46,6 +55,42 @@ static void balloon_page(void *addr, int deflate)
  #endif
  }

+/*
+ * reset_stats - Mark all items in the stats array as unset
+ *
+ * This function needs to be called at device intialization and before
+ * before updating to a set of newly-generated stats.  This will ensure that no
+ * stale values stick around in case the guest reports a subset of the 
supported
+ * statistics.
+ */
+static inline void reset_stats(VirtIOBalloon *dev)
+{
+    int i;
+    for (i = 0; i<  VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
+}
+
+static void stat_put(QDict *dict, const char *label, uint64_t val)
+{
+    if (val != -1)
+        qdict_put(dict, label, qint_from_int(val));
+}
+
+static QObject *get_stats_qobject(VirtIOBalloon *dev)
+{
+    QDict *dict = qdict_new();
+    uint32_t actual = ram_size - (dev->actual<<  VIRTIO_BALLOON_PFN_SHIFT);
+
+    stat_put(dict, "actual", actual);
+    stat_put(dict, "mem_swapped_in", dev->stats[VIRTIO_BALLOON_S_SWAP_IN]);
+    stat_put(dict, "mem_swapped_out", dev->stats[VIRTIO_BALLOON_S_SWAP_OUT]);
+    stat_put(dict, "major_page_faults", dev->stats[VIRTIO_BALLOON_S_MAJFLT]);
+    stat_put(dict, "minor_page_faults", dev->stats[VIRTIO_BALLOON_S_MINFLT]);
+    stat_put(dict, "free_mem", dev->stats[VIRTIO_BALLOON_S_MEMFREE]);
+    stat_put(dict, "total_mem", dev->stats[VIRTIO_BALLOON_S_MEMTOT]);
+
+    return QOBJECT(dict);
+}
+
  /* 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 +149,51 @@ static void virtio_balloon_handle_output(VirtIODevice 
*vdev, VirtQueue *vq)
      }
  }

+static void complete_stats_request(VirtIOBalloon *vb)
+{
+    QObject *stats;
+
+    if (!vb->stats_opaque_callback_data)
+        return;
+
+    stats = get_stats_qobject(vb);
+    vb->stats_callback(vb->stats_opaque_callback_data, stats);
+    qobject_decref(stats);
+    vb->stats_opaque_callback_data = NULL;
+    vb->stats_callback = NULL;
+}
+
+static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
+    VirtQueueElement *elem =&s->stats_vq_elem;
+    VirtIOBalloonStat stat;
+    size_t offset = 0;
+
+    if (!virtqueue_pop(vq, elem)) {
+        return;
+    }
+
+    /* Initialize the stats to get rid of any stale values.  This is only
+     * needed to handle the case where a guest supports fewer stats than it
+     * used to (ie. it has booted into an old kernel).
+     */
+    reset_stats(s);
+
+    while (memcpy_from_iovector(&stat, offset, sizeof(stat), elem->out_sg,
+                                elem->out_num) == sizeof(stat)) {
+        uint16_t tag = tswap16(stat.tag);
+        uint64_t val = tswap64(stat.val);
+
+        offset += sizeof(stat);
+        if (tag<  VIRTIO_BALLOON_S_NR)
+            s->stats[tag] = val;
+    }
+    s->stats_vq_offset = offset;
+
+    complete_stats_request(s);
+}
+
  static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t 
*config_data)
  {
      VirtIOBalloon *dev = to_virtio_balloon(vdev);
@@ -126,10 +216,12 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,

  static uint32_t virtio_balloon_get_features(VirtIODevice *vdev, uint32_t f)
  {
+    f |= (1<<  VIRTIO_BALLOON_F_STATS_VQ);
      return f;
  }

-static ram_addr_t virtio_balloon_to_target(void *opaque, ram_addr_t target)
+static void virtio_balloon_to_target(void *opaque, ram_addr_t target,
+                                     MonitorCompletion cb, void *cb_data)
  {
      VirtIOBalloon *dev = opaque;

@@ -139,9 +231,26 @@ 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 {
+        /* For now, only allow one request at a time.  This restriction can be
+         * removed later by queueing callback and data pairs.
+         */
+        if (dev->stats_callback != NULL) {
+            return;
+        }
+        dev->stats_callback = cb;
+        dev->stats_opaque_callback_data = cb_data;
+        if (dev->vdev.guest_features&  (1<<  VIRTIO_BALLOON_F_STATS_VQ)) {
+            virtqueue_push(dev->svq,&dev->stats_vq_elem, dev->stats_vq_offset);
+            virtio_notify(&dev->vdev, dev->svq);
+        } else {
+            /* Stats are not supported.  Clear out any stale values that might
+             * have been set by a more featureful guest kernel.
+             */
+            reset_stats(dev);
+            complete_stats_request(dev);
+        }
      }
-
-    return ram_size - (dev->actual<<  VIRTIO_BALLOON_PFN_SHIFT);
  }

  static void virtio_balloon_save(QEMUFile *f, void *opaque)
@@ -152,6 +261,10 @@ 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_buffer(f, (uint8_t *)&s->stats_callback, 
sizeof(MonitorCompletion));
+    qemu_put_buffer(f, (uint8_t *)&s->stats_opaque_callback_data, 
sizeof(void));
  }

  static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
@@ -165,6 +278,10 @@ 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));
+    qemu_get_buffer(f, (uint8_t *)&s->stats_callback, 
sizeof(MonitorCompletion));
+    qemu_get_buffer(f, (uint8_t *)&s->stats_opaque_callback_data, 
sizeof(void));

      return 0;
  }
@@ -183,7 +300,9 @@ 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);

+    reset_stats(s);
      qemu_add_balloon_handler(virtio_balloon_to_target, s);

      register_savevm("virtio-balloon", -1, 1, virtio_balloon_save, 
virtio_balloon_load, s);
diff --git a/hw/virtio-balloon.h b/hw/virtio-balloon.h
index 9a0d119..e20cf6b 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 +38,18 @@ struct virtio_balloon_config
      uint32_t actual;
  };

+/* Memory Statistics */
+#define VIRTIO_BALLOON_S_SWAP_IN  0   /* Amount of memory swapped in */
+#define VIRTIO_BALLOON_S_SWAP_OUT 1   /* Amount of memory swapped out */
+#define VIRTIO_BALLOON_S_MAJFLT   2   /* Number of major faults */
+#define VIRTIO_BALLOON_S_MINFLT   3   /* Number of minor faults */
+#define VIRTIO_BALLOON_S_MEMFREE  4   /* Total amount of free memory */
+#define VIRTIO_BALLOON_S_MEMTOT   5   /* Total amount of memory */
+#define VIRTIO_BALLOON_S_NR       6
+
+typedef struct VirtIOBalloonStat {
+    uint16_t tag;
+    uint64_t val;
+} __attribute__((packed)) VirtIOBalloonStat;
+
  #endif
diff --git a/monitor.c b/monitor.c
index 58cd02c..43a88fd 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2154,33 +2154,13 @@ static void do_info_status(Monitor *mon, QObject 
**ret_data)
                                      vm_running, singlestep);
  }

-static ram_addr_t balloon_get_value(void)
+static void print_balloon_stat(const char *key, QObject *obj, void *opaque)
  {
-    ram_addr_t actual;
-
-    if (kvm_enabled()&&  !kvm_has_sync_mmu()) {
-        qemu_error_new(QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
-        return 0;
-    }
-
-    actual = qemu_balloon_status();
-    if (actual == 0) {
-        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, "balloon");
-        return 0;
-    }
-
-    return actual;
-}
+    Monitor *mon = opaque;

-/**
- * do_balloon(): Request VM to change its memory allocation
- */
-static void do_balloon(Monitor *mon, const QDict *qdict, QObject **ret_data)
-{
-    if (balloon_get_value()) {
-        /* ballooning is active */
-        qemu_balloon(qdict_get_int(qdict, "value"));
-    }
+    if (strcmp(key, "actual"))
+        monitor_printf(mon, ",%s=%" PRId64, key,
+                       qint_get_int(qobject_to_qint(obj)));
  }

  static void monitor_print_balloon(Monitor *mon, const QObject *data)
@@ -2188,31 +2168,74 @@ static void monitor_print_balloon(Monitor *mon, const 
QObject *data)
      QDict *qdict;

      qdict = qobject_to_qdict(data);
+    if (!qdict_haskey(qdict, "actual"))
+        return;

-    monitor_printf(mon, "balloon: actual=%" PRId64 "\n",
-                        qdict_get_int(qdict, "balloon")>>  20);
+    monitor_printf(mon, "balloon: actual=%" PRId64,
+                   qdict_get_int(qdict, "actual")>>  20);
+    qdict_iter(qdict, print_balloon_stat, mon);
+    monitor_printf(mon, "\n");
  }

  /**
   * do_info_balloon(): Balloon information
   *
- * Return a QDict with the following information:
+ * Make an asynchronous request for balloon info.  When the request completes
+ * a QDict will be returned according to the following specification:
   *
- * - "balloon": current balloon value in bytes
+ * - "actual": current balloon value in bytes
+ * The following fields may or may not be present:
+ * - "mem_swapped_in": Amount of memory swapped in (bytes)
+ * - "mem_swapped_out": Amount of memory swapped out (bytes)
+ * - "major_page_faults": Number of major faults
+ * - "minor_page_faults": Number of minor faults
+ * - "free_mem": Total amount of free and unused memory (bytes)
+ * - "total_mem": Total amount of available memory (bytes)
   *
   * Example:
   *
- * { "balloon": 1073741824 }
+ * { "actual": 1073741824, "mem_swapped_in": 0, "mem_swapped_out": 0,
+ *   "major_page_faults": 142, "minor_page_faults": 239245,
+ *   "free_mem": 1014185984, "total_mem": 1044668416 }
+ */
+static int do_info_balloon(Monitor *mon, MonitorCompletion cb, void *opaque)
+{
+    int ret;
+
+    if (kvm_enabled()&&  !kvm_has_sync_mmu()) {
+        qemu_error_new(QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
+        return -1;
+    }
+
+    ret = qemu_balloon_status(cb, opaque);
+    if (!ret) {
+        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, "balloon");
+        return -1;
+    }
+
+    return 0;
+}
+
+/**
+ * do_balloon(): Request VM to change its memory allocation
   */
-static void do_info_balloon(Monitor *mon, QObject **ret_data)
+static int do_balloon(Monitor *mon, const QDict *params,
+                       MonitorCompletion cb, void *opaque)
  {
-    ram_addr_t actual;
+    int ret;
+
+    if (kvm_enabled()&&  !kvm_has_sync_mmu()) {
+        qemu_error_new(QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
+        return -1;
+    }

-    actual = balloon_get_value();
-    if (actual != 0) {
-        *ret_data = qobject_from_jsonf("{ 'balloon': %" PRId64 "}",
-                                       (int64_t) actual);
+    ret = qemu_balloon(qdict_get_int(params, "value"), cb, opaque);
+    if (ret == 0) {
+        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, "balloon");
+        return -1;
      }
+
+    return 0;
  }

  static qemu_acl *find_acl(Monitor *mon, const char *name)
@@ -2697,7 +2720,8 @@ static const mon_cmd_t info_cmds[] = {
          .params     = "",
          .help       = "show balloon information",
          .user_print = monitor_print_balloon,
-        .mhandler.info_new = do_info_balloon,
+        .mhandler.info_async = do_info_balloon,
+        .async      = 1,
      },
      {
          .name       = "qtree",
diff --git a/qemu-monitor.hx b/qemu-monitor.hx
index 1aa7818..62e6e81 100644
--- a/qemu-monitor.hx
+++ b/qemu-monitor.hx
@@ -890,7 +890,8 @@ ETEXI
          .params     = "target",
          .help       = "request VM to change it's memory allocation (in MB)",
          .user_print = monitor_user_noop,
-        .mhandler.cmd_new = do_balloon,
+        .mhandler.cmd_async = do_balloon,
+        .async      = 1,
      },

  STEXI
diff --git a/vl.c b/vl.c
index e070ec9..5c5b991 100644
--- a/vl.c
+++ b/vl.c
@@ -364,17 +364,24 @@ void qemu_add_balloon_handler(QEMUBalloonEvent *func, 
void *opaque)
      qemu_balloon_event_opaque = opaque;
  }

-void qemu_balloon(ram_addr_t target)
+int qemu_balloon(ram_addr_t target, MonitorCompletion cb, void *opaque)
  {
-    if (qemu_balloon_event)
-        qemu_balloon_event(qemu_balloon_event_opaque, target);
+    if (qemu_balloon_event) {
+        qemu_balloon_event(qemu_balloon_event_opaque, target, cb, opaque);
+        return 1;
+    } else {
+        return 0;
+    }
  }

-ram_addr_t qemu_balloon_status(void)
+int qemu_balloon_status(MonitorCompletion cb, void *opaque)
  {
-    if (qemu_balloon_event)
-        return qemu_balloon_event(qemu_balloon_event_opaque, 0);
-    return 0;
+    if (qemu_balloon_event) {
+        qemu_balloon_event(qemu_balloon_event_opaque, 0, cb, opaque);
+        return 1;
+    } else {
+        return 0;
+    }
  }









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