BLOCK MAP ERAS(9)

💖 Block map eras(9) 💖

okay so bestie, welcome to Block map eras(9) from the Kernel API Manual — section 9, kernel API vibes, very “I read source code for fun” energy ✨

The block map era, or maximum age, is used as follows:

Each block map page, when dirty, records the earliest recovery journal block sequence number of the changes reflected in that dirty block. Sequence numbers get classified into eras: every maximum_age sequence numbers, we switch to a new era. Block map pages are assigned to eras according to the sequence number they record. no cap, that’s the whole assignment system 🎀

In the current (newest) era, block map pages are not written unless there is cache pressure. In the next oldest era, each time a new journal block is written, 1/maximum_age of the pages in this era are issued for write. In all older eras, pages are issued for write immediately. 🦋

bestie tl;dr: newest era = chill unless cache pressure shows up; next oldest = little trickle writes; older eras = write immediately, periodt 💅

🌈 SEE ALSO 🌈

Kernel file ./drivers/md/dm-vdo/block-map.c

• initialize_info(9)
• allocate_cache_components(9)
• assert_on_cache_thread(9)
• get_page_state_name(9)
• update_counter(9)
• set_info_state(9)
• find_free_page(9)
• find_page(9)
• select_lru_page(9)
• complete_with_page(9)
• complete_waiter_with_error(9)
• complete_waiter_with_page(9)
• distribute_page_over_waitq(9)
• set_persistent_error(9)
• validate_completed_page(9)
• handle_load_error(9)
• page_is_loaded(9)
• handle_rebuild_read_error(9)
• launch_page_load(9)
• schedule_page_save(9)
• launch_page_save(9)
• completion_needs_page(9)
• allocate_free_page(9)
• discard_a_page(9)
• discard_page_if_needed(9)
• write_has_finished(9)
• handle_page_write_error(9)
• page_is_written_out(9)
• write_pages(9)
• vdo_release_page_completion(9)
• vdo_get_page(9)
• vdo_request_page_write(9)
• vdo_get_cached_page(9)
• vdo_invalidate_page_cache(9)
• get_tree_page_by_index(9)
• in_cyclic_range(9)
• is_not_older(9)
• add_to_dirty_lists(9)
• vdo_find_block_map_slot(9)
• make_forest(9)
• replace_forest(9)
• finish_cursor(9)
• continue_traversal(9)
• finish_traversal_load(9)
• traverse(9)
• launch_cursor(9)
• compute_boundary(9)
• vdo_traverse_forest(9)
• initialize_block_map_zone(9)
• clear_mapped_location(9)
• set_mapped_location(9)

that’s the whole page, bestie — signed from ./drivers/md/dm-vdo, dated October 2026 💅✨