[PATCH v9 0/7] NFS DIRECT: align misaligned DIO for LOCALIO

[Mike Snitzer <snitzer@kernel.org>]

Hi,

NFS and LOCALIO in particular benefit from avoiding the page cache for
workloads that have a working set that is significantly larger than
available system memory. NFS DIRECT makes it possible to always enable
LOCALIO to use O_DIRECT even if the IO is not DIO-aligned.

This patchset's changes are focused on NFS LOCALIO (fs/nfs/localio.c);
as such they will not impact NFS at all unless CONFIG_NFS_LOCALIO=y

Please give this patchset full consideration for merging upstream for
v6.18, I'll fully support this code now, into v6.18-rcX and beyond.

Changes since v8 (08.15.2025):
- Removed all fs/nfs/direct.c changes and pushed this misaligned DIO
  handling down to LOCALIO where it belongs.
- Updated all commit headers to reflect changes to code.
- Because misaligned DIO is now handled properly in LOCALIO, removed
  the nfs modparam 'localio_O_DIRECT_semantics' that was added during
  v6.14 to require users opt-in to the requirement that all O_DIRECT
  be properly DIO-aligned.
- Enhanced LOCALIO's DIO WRITE code to handle potential for VFS to
  return -ENOTBLK if it fails to invalidate page cache on WRITE.
- Verified various test IO workloads function as expected; including a
  misaligned DIO test that failed with the previous v8 direct.c
  implementation.
- Verified performance remains high with LOCALIO on fast NVMe.
- Verified sparse and checkpatch.pl are clean.

Earlier changelog was provided in v8's 0th patch header, see:
https://lore.kernel.org/linux-nfs/20250815233003.55071-1-snitzer@kernel.org/

All review appreciated, thanks.
Mike

Mike Snitzer (7):
  nfs/localio: make trace_nfs_local_open_fh more useful
  nfs/localio: avoid issuing misaligned IO using O_DIRECT
  nfs/localio: refactor iocb and iov_iter_bvec initialization
  nfs/localio: refactor iocb initialization further
  nfs/localio: add proper O_DIRECT support for READ and WRITE
  nfs/localio: add tracepoints for misaligned DIO READ and WRITE support
  NFS: add basic STATX_DIOALIGN and STATX_DIO_READ_ALIGN support

 fs/nfs/inode.c             |  15 ++
 fs/nfs/internal.h          |  10 +
 fs/nfs/localio.c           | 411 ++++++++++++++++++++++++++++---------
 fs/nfs/nfs3xdr.c           |   2 +-
 fs/nfs/nfstrace.h          |  76 ++++++-
 fs/nfsd/localio.c          |  11 +
 include/linux/nfslocalio.h |   2 +
 7 files changed, 426 insertions(+), 101 deletions(-)

-- 
2.44.0