Re: [PATCH v3 1/7] introduce 'track-writes-ram' migration capability

[Peter Xu <peterx@redhat.com>]

On Thu, Nov 19, 2020 at 03:59:34PM +0300, Andrey Gruzdev via wrote:
> Signed-off-by: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
> ---
>  migration/migration.c | 96 +++++++++++++++++++++++++++++++++++++++++++
>  migration/migration.h |  1 +
>  qapi/migration.json   |  7 +++-
>  3 files changed, 103 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 87a9b59f83..ff0364dde0 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -56,6 +56,7 @@
>  #include "net/announce.h"
>  #include "qemu/queue.h"
>  #include "multifd.h"
> +#include "sysemu/cpus.h"
>  
>  #ifdef CONFIG_VFIO
>  #include "hw/vfio/vfio-common.h"
> @@ -1165,6 +1166,91 @@ static bool migrate_caps_check(bool *cap_list,
>          }
>      }
>  
> +    if (cap_list[MIGRATION_CAPABILITY_TRACK_WRITES_RAM]) {
> +        if (cap_list[MIGRATION_CAPABILITY_POSTCOPY_RAM]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with postcopy-ram");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_DIRTY_BITMAPS]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with dirty-bitmaps");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_POSTCOPY_BLOCKTIME]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with postcopy-blocktime");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_LATE_BLOCK_ACTIVATE]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with late-block-activate");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_RETURN_PATH]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with return-path");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_MULTIFD]) {
> +            error_setg(errp, "Track-writes is not compatible with multifd");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_PAUSE_BEFORE_SWITCHOVER]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with pause-before-switchover");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_AUTO_CONVERGE]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with auto-converge");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_RELEASE_RAM]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with release-ram");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_RDMA_PIN_ALL]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with rdma-pin-all");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_COMPRESS]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with compression");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_XBZRLE]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with XBZLRE");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_X_COLO]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with x-colo");
> +            return false;
> +        }
> +
> +        if (cap_list[MIGRATION_CAPABILITY_VALIDATE_UUID]) {
> +            error_setg(errp,
> +                    "Track-writes is not compatible with validate-uuid");
> +            return false;
> +        }
> +    }
> +
>      return true;
>  }
>  
> @@ -2490,6 +2576,15 @@ bool migrate_use_block_incremental(void)
>      return s->parameters.block_incremental;
>  }
>  
> +bool migrate_track_writes_ram(void)
> +{
> +    MigrationState *s;
> +
> +    s = migrate_get_current();
> +
> +    return s->enabled_capabilities[MIGRATION_CAPABILITY_TRACK_WRITES_RAM];
> +}
> +
>  /* migration thread support */
>  /*
>   * Something bad happened to the RP stream, mark an error
> @@ -3783,6 +3878,7 @@ static Property migration_properties[] = {
>      DEFINE_PROP_MIG_CAP("x-block", MIGRATION_CAPABILITY_BLOCK),
>      DEFINE_PROP_MIG_CAP("x-return-path", MIGRATION_CAPABILITY_RETURN_PATH),
>      DEFINE_PROP_MIG_CAP("x-multifd", MIGRATION_CAPABILITY_MULTIFD),
> +    DEFINE_PROP_MIG_CAP("x-track-writes-ram", MIGRATION_CAPABILITY_TRACK_WRITES_RAM),
>  
>      DEFINE_PROP_END_OF_LIST(),
>  };
> diff --git a/migration/migration.h b/migration/migration.h
> index d096b77f74..339ae720e0 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -341,6 +341,7 @@ int migrate_compress_wait_thread(void);
>  int migrate_decompress_threads(void);
>  bool migrate_use_events(void);
>  bool migrate_postcopy_blocktime(void);
> +bool migrate_track_writes_ram(void);
>  
>  /* Sending on the return path - generic and then for each message type */
>  void migrate_send_rp_shut(MigrationIncomingState *mis,
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 3c75820527..a28d8b7ee8 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -442,6 +442,11 @@
>  # @validate-uuid: Send the UUID of the source to allow the destination
>  #                 to ensure it is the same. (since 4.2)
>  #
> +# @track-writes-ram: If enabled, the migration stream will be a snapshot
> +#                    of the VM exactly at the point when the migration
> +#                    procedure starts. The VM RAM is saved with running VM.
> +#                    (since 6.0)
> +#

The name is slightly confusing to me.  Could I ask why changed from previous
one?  "snapshot" sounds a very necessary keyword to me here and tells exactly
on what we do...  Because we can do quite a few things with "trace-writes-ram"
but not snapshotting, e.g., to calculate per-vm dirty rates.

-- 
Peter Xu