> @@ -317,7 +321,21 @@ static void coroutine_fn backup_run(void *opaque)
>                   if (alloced == 0) {
>                       continue;
>                   }
> +            } else if (job->sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
> +                int i, dirty = 0;
> +                for (i = 0; i < BACKUP_SECTORS_PER_CLUSTER;
> +                     i += job->sync_bitmap_gran) {
> +                    if (bdrv_get_dirty(bs, job->sync_bitmap,
> +                            start * BACKUP_SECTORS_PER_CLUSTER + i)) {
> +                        dirty = 1;
> +                        break;
> +                    }
> +                }
> +                if (!dirty) {
> +                    continue;
> +                }
>               }
> +
With such solution we don't use the power of HBitmap, which provides 
"hbitmap_iter_skip_words", with O(log(n)) complexity. Here we look 
through the whole bitmap (O(n)), instead of jumping to the next dirty bit.

-- 
С уважением,
Владимир