fastboot - platform/system/core - Git at Google

After generating the list of tasks to execute, Fastboot will try and
optimize the flashing of the dynamic partitions by constructing an
optimized flash super task. Fastboot will explicitly pattern match the
following commands and try and concatenate it into this task. (doing so
will allow us to avoid the reboot into userspace fastbootd which takes
significant time)

//Optimizable Block
reboot fastboot
update-super                        ---> generate optimized flash super task
$FOR EACH {dynamic partition}
    flash {dynamic partition}