Re: [PATCH v1 1/1] migration/colo.c: migrate dirty ram pages before colo checkpoint

[Derek Su <dereksu@qnap.com>]

Hello,

Ping...

Anyone have comments about this path?
To reduce the downtime during checkpoints, the patch tries to migrate 
memory page as many as possible just before entering COLO state.

Thanks.

Regards,
Derek

On 2020/6/21 上午10:10, Derek Su wrote:
> To reduce the guest's downtime during checkpoint, migrate dirty
> ram pages as many as possible before colo checkpoint.
> 
> If the iteration count reaches COLO_RAM_MIGRATE_ITERATION_MAX or
> ram pending size is lower than 'x-colo-migrate-ram-threshold',
> stop the ram migration and colo checkpoint.
> 
> Signed-off-by: Derek Su <dereksu@qnap.com>
> ---
>   migration/colo.c       | 79 ++++++++++++++++++++++++++++++++++++++++++
>   migration/migration.c  | 20 +++++++++++
>   migration/trace-events |  2 ++
>   monitor/hmp-cmds.c     |  8 +++++
>   qapi/migration.json    | 18 ++++++++--
>   5 files changed, 125 insertions(+), 2 deletions(-)
> 
> diff --git a/migration/colo.c b/migration/colo.c
> index ea7d1e9d4e..a0c71d7c56 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -46,6 +46,13 @@ static Notifier packets_compare_notifier;
>   static COLOMode last_colo_mode;
>   
>   #define COLO_BUFFER_BASE_SIZE (4 * 1024 * 1024)
> +#define COLO_RAM_MIGRATE_ITERATION_MAX 10
> +
> +typedef enum {
> +    COLO_MIG_ITERATE_RESUME = 0,  /* Resume migration iteration */
> +    COLO_MIG_ITERATE_BREAK  = 1,  /* Break migration loop */
> +} COLOMigIterateState;
> +
>   
>   bool migration_in_colo_state(void)
>   {
> @@ -398,6 +405,68 @@ static uint64_t colo_receive_message_value(QEMUFile *f, uint32_t expect_msg,
>       return value;
>   }
>   
> +static int colo_migrate_ram_iteration(MigrationState *s, Error **errp)
> +{
> +    int64_t threshold_size = s->parameters.x_colo_migrate_ram_threshold;
> +    uint64_t pending_size, pend_pre, pend_compat, pend_post;
> +    Error *local_err = NULL;
> +    int ret;
> +
> +    if (threshold_size == 0) {
> +        return COLO_MIG_ITERATE_BREAK;
> +    }
> +
> +    qemu_savevm_state_pending(s->to_dst_file, threshold_size,
> +                              &pend_pre, &pend_compat, &pend_post);
> +    pending_size = pend_pre + pend_compat + pend_post;
> +
> +    trace_colo_migrate_pending(pending_size, threshold_size,
> +                               pend_pre, pend_compat, pend_post);
> +
> +    /* Still a significant amount to transfer */
> +    if (pending_size && pending_size >= threshold_size) {
> +        colo_send_message(s->to_dst_file, COLO_MESSAGE_MIGRATE_RAM, &local_err);
> +        if (local_err) {
> +            error_propagate(errp, local_err);
> +            return COLO_MIG_ITERATE_BREAK;
> +        }
> +
> +        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(errp, -ret, "Failed to send dirty pages");
> +            return COLO_MIG_ITERATE_BREAK;
> +        }
> +
> +        return COLO_MIG_ITERATE_RESUME;
> +    }
> +
> +    trace_colo_migration_low_pending(pending_size);
> +
> +    return COLO_MIG_ITERATE_BREAK;
> +}
> +
> +static void colo_migrate_ram_before_checkpoint(MigrationState *s, Error **errp)
> +{
> +    Error *local_err = NULL;
> +    int iterate_count = 0;
> +
> +    while (iterate_count++ < COLO_RAM_MIGRATE_ITERATION_MAX) {
> +        COLOMigIterateState state;
> +
> +        state = colo_migrate_ram_iteration(s, &local_err);
> +        if (state == COLO_MIG_ITERATE_BREAK) {
> +            if (local_err) {
> +                error_propagate(errp, local_err);
> +            }
> +
> +            return;
> +        }
> +    };
> +}
> +
>   static int colo_do_checkpoint_transaction(MigrationState *s,
>                                             QIOChannelBuffer *bioc,
>                                             QEMUFile *fb)
> @@ -405,6 +474,11 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
>       Error *local_err = NULL;
>       int ret = -1;
>   
> +    colo_migrate_ram_before_checkpoint(s, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +
>       colo_send_message(s->to_dst_file, COLO_MESSAGE_CHECKPOINT_REQUEST,
>                         &local_err);
>       if (local_err) {
> @@ -819,6 +893,11 @@ 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:
> +        if (qemu_loadvm_state_main(mis->from_src_file, mis) < 0) {
> +            error_setg(errp, "Load ram failed");
> +        }
> +        break;
>       default:
>           error_setg(errp, "Got unknown COLO message: %d", msg);
>           break;
> diff --git a/migration/migration.c b/migration/migration.c
> index 481a590f72..390937ae5d 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -88,6 +88,7 @@
>   
>   /* The delay time (in ms) between two COLO checkpoints */
>   #define DEFAULT_MIGRATE_X_CHECKPOINT_DELAY (200 * 100)
> +#define DEFAULT_COLO_MIGRATE_RAM_THRESHOLD (100 * 1024 * 1024UL)
>   #define DEFAULT_MIGRATE_MULTIFD_CHANNELS 2
>   #define DEFAULT_MIGRATE_MULTIFD_COMPRESSION MULTIFD_COMPRESSION_NONE
>   /* 0: means nocompress, 1: best speed, ... 9: best compress ratio */
> @@ -800,6 +801,9 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
>       params->downtime_limit = s->parameters.downtime_limit;
>       params->has_x_checkpoint_delay = true;
>       params->x_checkpoint_delay = s->parameters.x_checkpoint_delay;
> +    params->has_x_colo_migrate_ram_threshold = true;
> +    params->x_colo_migrate_ram_threshold =
> +            s->parameters.x_colo_migrate_ram_threshold;
>       params->has_block_incremental = true;
>       params->block_incremental = s->parameters.block_incremental;
>       params->has_multifd_channels = true;
> @@ -1223,6 +1227,8 @@ static bool migrate_params_check(MigrationParameters *params, Error **errp)
>   
>       /* x_checkpoint_delay is now always positive */
>   
> +    /* x_colo_migrate_ram_threshold is zero or positive */
> +
>       if (params->has_multifd_channels && (params->multifd_channels < 1)) {
>           error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
>                      "multifd_channels",
> @@ -1356,6 +1362,11 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
>           dest->x_checkpoint_delay = params->x_checkpoint_delay;
>       }
>   
> +    if (params->has_x_colo_migrate_ram_threshold) {
> +        dest->x_colo_migrate_ram_threshold =
> +            params->x_colo_migrate_ram_threshold;
> +    }
> +
>       if (params->has_block_incremental) {
>           dest->block_incremental = params->block_incremental;
>       }
> @@ -1463,6 +1474,11 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
>           }
>       }
>   
> +    if (params->has_x_colo_migrate_ram_threshold) {
> +        s->parameters.x_colo_migrate_ram_threshold =
> +                params->x_colo_migrate_ram_threshold;
> +    }
> +
>       if (params->has_block_incremental) {
>           s->parameters.block_incremental = params->block_incremental;
>       }
> @@ -3622,6 +3638,9 @@ static Property migration_properties[] = {
>       DEFINE_PROP_UINT32("x-checkpoint-delay", MigrationState,
>                         parameters.x_checkpoint_delay,
>                         DEFAULT_MIGRATE_X_CHECKPOINT_DELAY),
> +    DEFINE_PROP_UINT64("x-colo-migrate-ram-threshold", MigrationState,
> +                      parameters.x_colo_migrate_ram_threshold,
> +                      DEFAULT_COLO_MIGRATE_RAM_THRESHOLD),
>       DEFINE_PROP_UINT8("multifd-channels", MigrationState,
>                         parameters.multifd_channels,
>                         DEFAULT_MIGRATE_MULTIFD_CHANNELS),
> @@ -3724,6 +3743,7 @@ static void migration_instance_init(Object *obj)
>       params->has_max_bandwidth = true;
>       params->has_downtime_limit = true;
>       params->has_x_checkpoint_delay = true;
> +    params->has_x_colo_migrate_ram_threshold = true;
>       params->has_block_incremental = true;
>       params->has_multifd_channels = true;
>       params->has_multifd_compression = true;
> diff --git a/migration/trace-events b/migration/trace-events
> index 4ab0a503d2..32bf42cdb3 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -295,6 +295,8 @@ 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_migrate_pending(uint64_t size, uint64_t max, uint64_t pre, uint64_t compat, uint64_t post) "pending size %" PRIu64 " max %" PRIu64 " (pre = %" PRIu64 " compat=%" PRIu64 " post=%" PRIu64 ")"
> +colo_migration_low_pending(uint64_t pending) "%" PRIu64
>   
>   # colo-failover.c
>   colo_failover_set_state(const char *new_state) "new state %s"
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index e03adf0d4d..ebca533960 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -450,6 +450,10 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
>           monitor_printf(mon, "%s: %u\n",
>               MigrationParameter_str(MIGRATION_PARAMETER_X_CHECKPOINT_DELAY),
>               params->x_checkpoint_delay);
> +        assert(params->has_x_colo_migrate_ram_threshold);
> +        monitor_printf(mon, "%s: %" PRIu64 "\n",
> +            MigrationParameter_str(MIGRATION_PARAMETER_X_COLO_MIGRATE_RAM_THRESHOLD),
> +            params->x_colo_migrate_ram_threshold);
>           assert(params->has_block_incremental);
>           monitor_printf(mon, "%s: %s\n",
>               MigrationParameter_str(MIGRATION_PARAMETER_BLOCK_INCREMENTAL),
> @@ -1330,6 +1334,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
>           p->has_x_checkpoint_delay = true;
>           visit_type_int(v, param, &p->x_checkpoint_delay, &err);
>           break;
> +    case MIGRATION_PARAMETER_X_COLO_MIGRATE_RAM_THRESHOLD:
> +        p->has_x_colo_migrate_ram_threshold = true;
> +        visit_type_int(v, param, &p->x_colo_migrate_ram_threshold, &err);
> +        break;
>       case MIGRATION_PARAMETER_BLOCK_INCREMENTAL:
>           p->has_block_incremental = true;
>           visit_type_bool(v, param, &p->block_incremental, &err);
> diff --git a/qapi/migration.json b/qapi/migration.json
> index d5000558c6..30576c038c 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -600,6 +600,9 @@
>   # @x-checkpoint-delay: The delay time (in ms) between two COLO checkpoints in
>   #                      periodic mode. (Since 2.8)
>   #
> +# @x-colo-migrate-ram-threshold: the threshold (in bytes) of the COLO ram migration's
> +#                                pending size before COLO checkpoint. (Since 5.0)
> +#
>   # @block-incremental: Affects how much storage is migrated when the
>   #                     block migration capability is enabled.  When false, the entire
>   #                     storage backing chain is migrated into a flattened image at
> @@ -651,7 +654,8 @@
>              'cpu-throttle-initial', 'cpu-throttle-increment',
>              'cpu-throttle-tailslow',
>              'tls-creds', 'tls-hostname', 'tls-authz', 'max-bandwidth',
> -           'downtime-limit', 'x-checkpoint-delay', 'block-incremental',
> +           'downtime-limit', 'x-checkpoint-delay',
> +           'x-colo-migrate-ram-threshold', 'block-incremental',
>              'multifd-channels',
>              'xbzrle-cache-size', 'max-postcopy-bandwidth',
>              'max-cpu-throttle', 'multifd-compression',
> @@ -740,6 +744,9 @@
>   #
>   # @x-checkpoint-delay: the delay time between two COLO checkpoints. (Since 2.8)
>   #
> +# @x-colo-migrate-ram-threshold: the threshold in bytes of the COLO ram migration's
> +#                                pending size before COLO checkpoint. (Since 5.0)
> +#
>   # @block-incremental: Affects how much storage is migrated when the
>   #                     block migration capability is enabled.  When false, the entire
>   #                     storage backing chain is migrated into a flattened image at
> @@ -804,6 +811,7 @@
>               '*max-bandwidth': 'int',
>               '*downtime-limit': 'int',
>               '*x-checkpoint-delay': 'int',
> +            '*x-colo-migrate-ram-threshold': 'int',
>               '*block-incremental': 'bool',
>               '*multifd-channels': 'int',
>               '*xbzrle-cache-size': 'size',
> @@ -915,6 +923,9 @@
>   #
>   # @x-checkpoint-delay: the delay time between two COLO checkpoints. (Since 2.8)
>   #
> +# @x-colo-migrate-ram-threshold: the threshold in bytes of the COLO ram migration's
> +#                                pending size before COLO checkpoint. (Since 5.0)
> +#
>   # @block-incremental: Affects how much storage is migrated when the
>   #                     block migration capability is enabled.  When false, the entire
>   #                     storage backing chain is migrated into a flattened image at
> @@ -978,6 +989,7 @@
>               '*max-bandwidth': 'size',
>               '*downtime-limit': 'uint64',
>               '*x-checkpoint-delay': 'uint32',
> +            '*x-colo-migrate-ram-threshold': 'uint64',
>               '*block-incremental': 'bool' ,
>               '*multifd-channels': 'uint8',
>               '*xbzrle-cache-size': 'size',
> @@ -1116,12 +1128,14 @@
>   #
>   # @vmstate-loaded: VM's state has been loaded by SVM.
>   #
> +# @migrate-ram: Send dirty pages as many as possible before 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' ] }
>   
>   ##
>   # @COLOMode:
>