[PATCH V2 7/8] COLO: Migrate dirty pages during the gap of checkpointing

[zhanghailiang <zhang.zhanghailiang@huawei.com>]

We can migrate some dirty pages during the gap of checkpointing,
by this way, we can reduce the amount of ram migrated during checkpointing.

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
---
 migration/colo.c       | 73 ++++++++++++++++++++++++++++++++++++++++--
 migration/migration.h  |  1 +
 migration/trace-events |  1 +
 qapi/migration.json    |  4 ++-
 4 files changed, 75 insertions(+), 4 deletions(-)

diff --git a/migration/colo.c b/migration/colo.c
index 44942c4e23..c36d94072f 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -47,6 +47,13 @@ static COLOMode last_colo_mode;
 
 #define COLO_BUFFER_BASE_SIZE (4 * 1024 * 1024)
 
+#define DEFAULT_RAM_PENDING_CHECK 1000
+
+/* should be calculated by bandwidth and max downtime ? */
+#define THRESHOLD_PENDING_SIZE (100 * 1024 * 1024UL)
+
+static int checkpoint_request;
+
 bool migration_in_colo_state(void)
 {
     MigrationState *s = migrate_get_current();
@@ -517,6 +524,20 @@ static void colo_compare_notify_checkpoint(Notifier *notifier, void *data)
     colo_checkpoint_notify(data);
 }
 
+static bool colo_need_migrate_ram_background(MigrationState *s)
+{
+    uint64_t pending_size, pend_pre, pend_compat, pend_post;
+    int64_t max_size = THRESHOLD_PENDING_SIZE;
+
+    qemu_savevm_state_pending(s->to_dst_file, max_size, &pend_pre,
+                              &pend_compat, &pend_post);
+    pending_size = pend_pre + pend_compat + pend_post;
+
+    trace_colo_need_migrate_ram_background(pending_size);
+    return (pending_size >= max_size);
+}
+
+
 static void colo_process_checkpoint(MigrationState *s)
 {
     QIOChannelBuffer *bioc;
@@ -572,6 +593,8 @@ static void colo_process_checkpoint(MigrationState *s)
 
     timer_mod(s->colo_delay_timer,
             current_time + s->parameters.x_checkpoint_delay);
+    timer_mod(s->pending_ram_check_timer,
+        current_time + DEFAULT_RAM_PENDING_CHECK);
 
     while (s->state == MIGRATION_STATUS_COLO) {
         if (failover_get_state() != FAILOVER_STATUS_NONE) {
@@ -584,9 +607,30 @@ static void colo_process_checkpoint(MigrationState *s)
         if (s->state != MIGRATION_STATUS_COLO) {
             goto out;
         }
-        ret = colo_do_checkpoint_transaction(s, bioc, fb);
-        if (ret < 0) {
-            goto out;
+        if (atomic_xchg(&checkpoint_request, 0)) {
+            /* start a colo checkpoint */
+            ret = colo_do_checkpoint_transaction(s, bioc, fb);
+            if (ret < 0) {
+                goto out;
+            }
+        } else {
+            if (colo_need_migrate_ram_background(s)) {
+                colo_send_message(s->to_dst_file,
+                                  COLO_MESSAGE_MIGRATE_RAM_BACKGROUND,
+                                  &local_err);
+                if (local_err) {
+                    goto out;
+                }
+
+                qemu_savevm_state_iterate(s->to_dst_file, false);
+                qemu_put_byte(s->to_dst_file, QEMU_VM_EOF);
+                ret = qemu_file_get_error(s->to_dst_file);
+                if (ret < 0) {
+                    error_setg_errno(&local_err, -ret,
+                        "Failed to send dirty pages backgroud");
+                    goto out;
+                }
+            }
         }
     }
 
@@ -627,6 +671,8 @@ out:
     colo_compare_unregister_notifier(&packets_compare_notifier);
     timer_del(s->colo_delay_timer);
     timer_free(s->colo_delay_timer);
+    timer_del(s->pending_ram_check_timer);
+    timer_free(s->pending_ram_check_timer);
     qemu_sem_destroy(&s->colo_checkpoint_sem);
 
     /*
@@ -644,6 +690,7 @@ void colo_checkpoint_notify(void *opaque)
     MigrationState *s = opaque;
     int64_t next_notify_time;
 
+    atomic_inc(&checkpoint_request);
     qemu_sem_post(&s->colo_checkpoint_sem);
     s->colo_checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
     next_notify_time = s->colo_checkpoint_time +
@@ -651,6 +698,19 @@ void colo_checkpoint_notify(void *opaque)
     timer_mod(s->colo_delay_timer, next_notify_time);
 }
 
+static void colo_pending_ram_check_notify(void *opaque)
+{
+    int64_t next_notify_time;
+    MigrationState *s = opaque;
+
+    if (migration_in_colo_state()) {
+        next_notify_time = DEFAULT_RAM_PENDING_CHECK +
+                           qemu_clock_get_ms(QEMU_CLOCK_HOST);
+        timer_mod(s->pending_ram_check_timer, next_notify_time);
+        qemu_sem_post(&s->colo_checkpoint_sem);
+    }
+}
+
 void migrate_start_colo_process(MigrationState *s)
 {
     qemu_mutex_unlock_iothread();
@@ -658,6 +718,8 @@ void migrate_start_colo_process(MigrationState *s)
     s->colo_delay_timer =  timer_new_ms(QEMU_CLOCK_HOST,
                                 colo_checkpoint_notify, s);
 
+    s->pending_ram_check_timer = timer_new_ms(QEMU_CLOCK_HOST,
+                                colo_pending_ram_check_notify, s);
     qemu_sem_init(&s->colo_exit_sem, 0);
     migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_COLO);
@@ -806,6 +868,11 @@ static void colo_wait_handle_message(MigrationIncomingState *mis,
     case COLO_MESSAGE_CHECKPOINT_REQUEST:
         colo_incoming_process_checkpoint(mis, fb, bioc, errp);
         break;
+    case COLO_MESSAGE_MIGRATE_RAM_BACKGROUND:
+        if (qemu_loadvm_state_main(mis->from_src_file, mis) < 0) {
+            error_setg(errp, "Load ram background failed");
+        }
+        break;
     default:
         error_setg(errp, "Got unknown COLO message: %d", msg);
         break;
diff --git a/migration/migration.h b/migration/migration.h
index 8473ddfc88..5355259789 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -219,6 +219,7 @@ struct MigrationState
     QemuSemaphore colo_checkpoint_sem;
     int64_t colo_checkpoint_time;
     QEMUTimer *colo_delay_timer;
+    QEMUTimer *pending_ram_check_timer;
 
     /* The first error that has occurred.
        We used the mutex to be able to return the 1st error message */
diff --git a/migration/trace-events b/migration/trace-events
index 4ab0a503d2..f2ed0c8645 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -295,6 +295,7 @@ migration_tls_incoming_handshake_complete(void) ""
 colo_vm_state_change(const char *old, const char *new) "Change '%s' => '%s'"
 colo_send_message(const char *msg) "Send '%s' message"
 colo_receive_message(const char *msg) "Receive '%s' message"
+colo_need_migrate_ram_background(uint64_t pending_size) "Pending 0x%" PRIx64 " dirty ram"
 
 # colo-failover.c
 colo_failover_set_state(const char *new_state) "new state %s"
diff --git a/qapi/migration.json b/qapi/migration.json
index 52f3429969..73445f1978 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -977,12 +977,14 @@
 #
 # @vmstate-loaded: VM's state has been loaded by SVM.
 #
+# @migrate-ram-background: Send some dirty pages during the gap of COLO checkpoint
+#
 # Since: 2.8
 ##
 { 'enum': 'COLOMessage',
   'data': [ 'checkpoint-ready', 'checkpoint-request', 'checkpoint-reply',
             'vmstate-send', 'vmstate-size', 'vmstate-received',
-            'vmstate-loaded' ] }
+            'vmstate-loaded', 'migrate-ram-background' ] }
 
 ##
 # @COLOMode:
-- 
2.21.0