InnoDB is issuing writes to buffer pool pages and redo log, which are not actually modifying anything. Here are some examples:

• fsp_alloc_seg_inode_page() is unnecessarily zero-initializing FSEG_ID, which is already zero-initialized since MySQL 5.1.48 or MariaDB 5.1.49.
• btr_store_big_rec_extern_fields() is zero-initializing the most significant 32 bits of BTR_EXTERN_LEN, even though the field is zero-initialized in the BLOB pointer at least since MySQL 5.5.42, MariaDB 5.5.42.
• The function rtr_adjust_upper_level(), introduced in MySQL 5.7.5 and MariaDB 10.2.2, appears to be unnecessarily retrieving and null-modifying the preceding page (prev_page_no).