[PATCH v11 0/3] NFSD: Implement NFSD_IO_DIRECT for NFS WRITE

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

Following on https://lore.kernel.org/linux-nfs/aPAci7O_XK1ljaum@kernel.org/
this series includes the patches needed to make NFSD Direct WRITE
operational.

After applying Christoph's patch, I looked at restoring the comment
block in front of iov_iter_bvec_offset(), but it seems to make
slightly more sense to leave it where it is in
nfsd_write_dio_iters_init().

I'm still looking into Neil's comment about adding a trace point
for unaligned segments.

One controversy remains: Whether to set DONTCACHE for the unaligned
segments.

I still see this during fstests runs with NFSD_IO_DIRECT enabled:

WARNING: CPU: 5 PID: 1309 at fs/iomap/buffered-io.c:1402 iomap_zero_iter+0x1a4/0x390

No new test failures, but I need to narrow down which test is
triggering this message.

Applies on: 7f7d8421c7fa2588930146cb461e3e069658ced9
In the branch https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/log/?h=nfsd-testing


Changes since v10:
* Applied Christoph's clean-ups
* Applied Mike's documentation fixes

Changes since v9:
* Unaligned segments no longer use IOCB_DONTCACHE
* Squashed all review patches into Mike's initial patch
* Squashed Mike's documentation update into the final patch

Changes since v8:
* Drop "NFSD: Handle both offset and memory alignment for direct I/O"
* Include the Sep 3 version of the Documentation update

Changes since v7:
* Rebase the series on Mike's original v3 patch
* Address more review comments
* Optimize the "when can NFSD use IOCB_DIRECT" logic
* Revert the "always promote to FILE_SYNC" logic

Changes since v6:
* Patches to address review comments have been split out
* Refactored the iter initialization code

Changes since v5:
* Add a patch to make FILE_SYNC WRITEs persist timestamps
* Address some of Christoph's review comments
* The svcrdma patch has been dropped until we actually need it

Changes since v4:
* Split out refactoring nfsd_buffered_write() into a separate patch
* Expand patch description of 1/4
* Don't set IOCB_SYNC flag

Changes since v3:
* Address checkpatch.pl nits in 2/3
* Add an untested patch to mark ingress RDMA Read chunks

Chuck Lever (1):
  NFSD: Make FILE_SYNC WRITEs comply with spec

Mike Snitzer (2):
  NFSD: Implement NFSD_IO_DIRECT for NFS WRITE
  NFSD: add Documentation/filesystems/nfs/nfsd-io-modes.rst

 .../filesystems/nfs/nfsd-io-modes.rst         | 144 ++++++++++++++++
 fs/nfsd/debugfs.c                             |   1 +
 fs/nfsd/trace.h                               |   1 +
 fs/nfsd/vfs.c                                 | 154 +++++++++++++++++-
 4 files changed, 294 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/filesystems/nfs/nfsd-io-modes.rst

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