[PATCH v4 0/3] Initial NFS client support for RWF_DONTCACHE

[Trond Myklebust <trondmy@kernel.org>]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

The following patch set attempts to add support for the RWF_DONTCACHE
flag in preadv2() and pwritev2() on NFS filesystems.

The main issue is allowing support on 2 stage writes (i.e. unstable
WRITE followed by a COMMIT) since those don't follow the current
assumption that the 'dropbehind' flag can be fulfilled as soon as the
writeback lock is dropped.

v2:
 - Make use of the new iocb parameter for nfs_write_begin()
v3:
 - Set/clear PG_DROPBEHIND on the head of the nfs_page group
 - Simplify helper folio_end_dropbehind
v4:
 - Replace filemap_end_dropbehind_write() with folio_end_dropbehind()
 - Add a helper to replace folio_end_writeback with an equivalent that
   does not attempt to interpret the dropbehind flag
 - Keep the folio dropbehind flag set until the NFS client is ready to
   call folio_end_dropbehind.
 - Don't try to do a read-modify-write in nfs_write_begin() if the folio
   has the dropbehind flag set.

Trond Myklebust (3):
  filemap: Add a helper for filesystems implementing dropbehind
  filemap: Add a version of folio_end_writeback that ignores dropbehind
  NFS: Enable use of the RWF_DONTCACHE flag on the NFS client

 fs/nfs/file.c           |  9 +++++----
 fs/nfs/nfs4file.c       |  1 +
 fs/nfs/write.c          |  4 +++-
 include/linux/pagemap.h |  2 ++
 mm/filemap.c            | 34 ++++++++++++++++++++++++++--------
 5 files changed, 37 insertions(+), 13 deletions(-)

-- 
2.50.1