Re: [RFC PATCH 0/3] Initial NFS client support for RWF_DONTCACHE

[Chuck Lever <chuck.lever@oracle.com>]

On 4/23/25 12:25 AM, trondmy@kernel.org wrote:
> 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.

Hi Trond-

"RFC" in the subject field noted.

The cover letter does not explain why one would want this facility, nor
does it quantify the performance implications.

I can understand not wanting to cache on an NFS server, but don't you
want to maintain a data cache as close to applications as possible?


> 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.
> 
> Trond Myklebust (3):
>   filemap: Add a helper for filesystems implementing dropbehind
>   filemap: Mark folios as dropbehind in generic_perform_write()
>   NFS: Enable the RWF_DONTCACHE flag for the NFS client
> 
>  fs/nfs/file.c            |  2 ++
>  fs/nfs/nfs4file.c        |  2 ++
>  fs/nfs/write.c           | 12 +++++++++++-
>  include/linux/nfs_page.h |  1 +
>  include/linux/pagemap.h  |  1 +
>  mm/filemap.c             | 21 +++++++++++++++++++++
>  6 files changed, 38 insertions(+), 1 deletion(-)
> 


-- 
Chuck Lever