rwf-dontcache · shipping · also uncached buffered I/O, buffered I/O drop-behind

RWF_DONTCACHE

RWF_DONTCACHE is a Linux per-operation flag requesting best-effort removal of page-cache content newly instantiated by a buffered read or write.

Related Observatory article: RWF_DONTCACHE on hesela.com

The flag is documented since Linux 6.14; previously cached ranges are not pruned by the hint, and unsupported targets report EOPNOTSUPP. Writes initiate writeback, which is not a durability guarantee. [1] The v6.14 filemap_read path still copies cached folios to the caller before attempting drop-behind; this is not O_DIRECT or proof of zero-copy transfer. [2]

Relations

related

buffered-io, page-cache, direct-io, posix-fadv-noreuse, posix-fadv-dontneed, fsync

Advantages

• Can limit cache retention for one-pass buffered access while retaining already cached ranges.

Limitations

• No hard guarantee of final cache state, durable completion or improved throughput.

Citations

1. Linux man-pages 6.19: readv(2), RWF_DONTCACHE and RWF_DSYNC/RWF_SYNC. (accessed 2026-10-15)
2. Linux v6.14 mm/filemap.c: filemap_read and drop-behind read completion. (accessed 2026-10-15)

JSON: /data/terms/rwf-dontcache.json