f2fs-segment-information-table · shipping · also F2FS SIT

F2FS Segment Information Table

The F2FS Segment Information Table records segment-level block validity information used in space management and cleaning.

In Linux v6.12, an on-disk SIT entry contains a validity bitmap, a field encoding valid-block count and allocation type, and a segment-age field. A validity bit concerns allocation state, not verification of the block's payload against a checksum. [1]

The in-memory seg_entry separately tracks current and checkpoint-valid block counts and maps. These are not interchangeable observations. The in-memory ckpt_valid_map is not always a frozen last-checkpoint image: enabled-checkpoint allocation can set its bits, and SSR excludes positions set in either map. [4] [2]

Relations

related

F2FS, F2FS Node Address Table, F2FS Segment Summary Area, F2FS checkpoint, Host-side flash GC, F2FS slack space recycling

Citations

1. Linux v6.12 include/linux/f2fs_fs.h: NAT, SIT and summary entry formats. (accessed 2026-10-21)
2. Linux v6.12 fs/f2fs/segment.h: seg_entry and current/checkpoint validity maps. (accessed 2026-10-21)
4. Linux v6.12 fs/f2fs/segment.c: update_sit_entry, __next_free_blkoff and change_curseg. (accessed 2026-10-21)

Further reading

3. F2FS: when a successful fsync is not a recovery promise (accessed 2026-10-21)

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