Re: [PATCH RFC 2/2] nfsd: call generic_fadvise after v3 READ, stable WRITE or COMMIT

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Jul 03, 2025 at 04:07:51PM -0400, Chuck Lever wrote:
> On 7/3/25 3:53 PM, Jeff Layton wrote:
> > Recent testing has shown that keeping pagecache pages around for too
> > long can be detrimental to performance with nfsd. Clients only rarely
> > revisit the same data, so the pages tend to just hang around.
> > 
> > This patch changes the pc_release callbacks for NFSv3 READ, WRITE and
> > COMMIT to call generic_fadvise(..., POSIX_FADV_DONTNEED) on the accessed
> > range.
> > 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/nfsd/debugfs.c  |  2 ++
> >  fs/nfsd/nfs3proc.c | 59 +++++++++++++++++++++++++++++++++++++++++++++---------
> >  fs/nfsd/nfsd.h     |  1 +
> >  fs/nfsd/nfsproc.c  |  4 ++--
> >  fs/nfsd/vfs.c      | 21 ++++++++++++++-----
> >  fs/nfsd/vfs.h      |  5 +++--
> >  fs/nfsd/xdr3.h     |  3 +++
> >  7 files changed, 77 insertions(+), 18 deletions(-)
> > 
> > diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
> > index 84b0c8b559dc90bd5c2d9d5e15c8e0682c0d610c..b007718dd959bc081166ec84e06f577a8fc2b46b 100644
> > --- a/fs/nfsd/debugfs.c
> > +++ b/fs/nfsd/debugfs.c
> > @@ -44,4 +44,6 @@ void nfsd_debugfs_init(void)
> >  
> >  	debugfs_create_file("disable-splice-read", S_IWUSR | S_IRUGO,
> >  			    nfsd_top_dir, NULL, &nfsd_dsr_fops);
> > +	debugfs_create_bool("enable-fadvise-dontneed", 0644,
> > +			    nfsd_top_dir, &nfsd_enable_fadvise_dontneed);
> 
> I prefer that this setting is folded into the new io_cache_read /
> io_cache_write tune-ables that Mike's patch adds, rather than adding
> a new boolean.
> 
> That might make a hybrid "DONTCACHE for READ and fadvise for WRITE"
> pretty easy.

That'd be really easy.  Jeff, maybe have a look to rebase your changes
on this patchset:
https://lore.kernel.org/linux-nfs/20250708160619.64800-1-snitzer@kernel.org/

Ontop of this patch in particular:
https://lore.kernel.org/linux-nfs/20250708160619.64800-8-snitzer@kernel.org/

My git branch with this patchset at the tip is available here:
https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/log/?h=kernel-6.12.24/nfsd-testing-snitm

Mike