Re: [PATCH for-6.0 v1 1/4] migration: Fix missing qemu_fflush() on buffer file in bg_migration_thread

[Dr. David Alan Gilbert]

* Andrey Gruzdev (andrey.gruzdev@virtuozzo.com) wrote:
> Added missing qemu_fflush() on buffer file holding precopy device state.
> Increased initial QIOChannelBuffer allocation to 512KB to avoid reallocs.
> Typical configurations often require >200KB for device state and VMDESC.
> 
> Fixes: 8518278a6af589ccc401f06e35f171b1e6fae800 (migration: implementation
>   of background snapshot thread)
> Signed-off-by: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/migration.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index ca8b97baa5..00e13f9d58 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -3812,7 +3812,7 @@ static void *bg_migration_thread(void *opaque)
>       * with vCPUs running and, finally, write stashed non-RAM part of
>       * the vmstate from the buffer to the migration stream.
>       */
> -    s->bioc = qio_channel_buffer_new(128 * 1024);
> +    s->bioc = qio_channel_buffer_new(512 * 1024);
>      qio_channel_set_name(QIO_CHANNEL(s->bioc), "vmstate-buffer");
>      fb = qemu_fopen_channel_output(QIO_CHANNEL(s->bioc));
>      object_unref(OBJECT(s->bioc));
> @@ -3866,6 +3866,12 @@ static void *bg_migration_thread(void *opaque)
>      if (qemu_savevm_state_complete_precopy_non_iterable(fb, false, false)) {
>          goto fail;
>      }
> +    /*
> +     * Since we are going to get non-iterable state data directly
> +     * from s->bioc->data, explicit flush is needed here.
> +     */
> +    qemu_fflush(fb);
> +
>      /* Now initialize UFFD context and start tracking RAM writes */
>      if (ram_write_tracking_start()) {
>          goto fail;
> -- 
> 2.27.0
> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK