rwf-hipri · shipping

RWF_HIPRI

RWF_HIPRI is a Linux per-operation flag permitting completion polling for eligible direct I/O.

The flag is documented since Linux 4.6 for preadv2/pwritev2 on O_DIRECT descriptors. Unlike RWF_NOWAIT, it does not request an immediate result when a read would need to wait. [1]

In Linux v6.14, the VFS iterator path initializes a synchronous kiocb. The iomap submission helper marks a BIO for polling only when IOCB_HIPRI is set and that kiocb is not synchronous. A synchronous request reaching this helper therefore cannot take that polling branch. Acceptance of the flag is not evidence that polling occurred. [2] [3] [4]

Relations

related
Direct I/O, I/O completion polling, RWF_NOWAIT, io_uring

Limitations

  • The flag alone supplies no durability contract or guaranteed latency reduction.

Citations

  1. Linux man-pages 6.19: readv(2), RWF_HIPRI and RWF_NOWAIT (accessed 2026-11-10)
  2. Linux v6.14: do_iter_readv_writev and preadv2/pwritev2 dispatch (accessed 2026-11-10)
  3. Linux v6.14: init_sync_kiocb, is_sync_kiocb and kiocb_set_rw_flags (accessed 2026-11-10)
  4. Linux v6.14: iomap_dio_submit_bio polling eligibility (accessed 2026-11-10)

Further reading

  1. Hesela: distinguish completion polling from submission polling and NOWAIT (accessed 2026-11-10)
Sources & caveats
  • The implementation trace is pinned to Linux v6.14; it is not a hardware measurement or a claim about every filesystem and kernel. [2] [3] [4]

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Hesela team. RWF_HIPRI. Hesela. 2026-11-10. https://hesela.dev/terms/rwf-hipri/