Are piggybacking of write and redirection of read available in md driver now?

there were two optimizations-redirection of reads and piggybacking of
writes-which first introduced in paper "Performance Analysis of Disk
Arrays under Failure" 16th VLDB conference 1990.

redirection of reads: the user accesses to data that has already been
reconstructed are serviced by (redirected to) the replacement disk,
rather than invoking on-the-fly reconstruction as they would if the
data were not yet available.
piggybacking of writes: the user reads that cause on-the-fly
reconstruction also cause the reconstructed data to be written to the
replacement disk.

have these two features been implemented in md driver now? if so,
where i can find them? if not, is there any plan on them?

Thanks