+ size_t psize = env->me_psize, sz = psize, off;
+ /* For ! #MDB_NOMEMINIT, psize counts how much to init.
+ * For a single page alloc, we init everything after the page header.
+ * For multi-page, we init the final page; if the caller needed that
+ * many pages they will be filling in at least up to the last page.
+ */