When a InnoDB data file page is freed, its contents becomes garbage, and any storage allocated in the data file is wasted.
We should introduce an InnoDB redo log record for marking pages as freed. This record, MLOG_INIT_FREE_PAGE, could be treated as no-op, or we could elect to punch a hole, especially when the page_compressed=1 option is used.
If scrubbing is enabled, we should initialize the page with zeros. This should replace some of the non-working scrubbing logic (MDEV-8139).