Re: (subset) [PATCH v5 00/13] NFSD DIRECT and NFS DIRECT

[Mike Snitzer <snitzer@kernel.org>]

On Sun, Jul 27, 2025 at 12:16:04PM -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> On Thu, 24 Jul 2025 15:30:49 -0400, Mike Snitzer wrote:
> > Some workloads benefit from NFSD avoiding the page cache, particularly
> > those with a working set that is significantly larger than available
> > system memory.  This patchset introduces _optional_ support to
> > configure the use of O_DIRECT or DONTCACHE for NFSD's READ and WRITE
> > support.  The NFSD default to use page cache is left unchanged.
> > 
> > The performance win associated with using NFSD DIRECT was previously
> > summarized here:
> > https://lore.kernel.org/linux-nfs/aEslwqa9iMeZjjlV@kernel.org/
> > This picture offers a nice summary of performance gains:
> > https://original.art/NFSD_direct_vs_buffered_IO.jpg
> > 
> > [...]
> 
> Applied to nfsd-testing, thanks!
> 
> [01/13] NFSD: filecache: add STATX_DIOALIGN and STATX_DIO_READ_ALIGN support
>         commit: af157e09634a113da83d8ac5fff541f9e06ad653

> [05/13] NFSD: filecache: only get DIO alignment attrs if NFSD_IO_DIRECT enabled
>         commit: af157e09634a113da83d8ac5fff541f9e06ad653

I noticed you folded these, unfortunately that isn't bisect safe
unless you pull these fs/nfsd/nfsd.h changes to the front too:

git diff f76b72e4908c556021d94bdeca86fffce430c791^..a45da44bb6bade1dfef569c792ae2ee6507f4724 -- fs/nfsd/nfsd.h

diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 1cd0bed57bc2..fe935b4cda53 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -153,6 +153,16 @@ static inline void nfsd_debugfs_exit(void) {}
 
 extern bool nfsd_disable_splice_read __read_mostly;
 
+enum {
+	NFSD_IO_UNSPECIFIED = 0,
+	NFSD_IO_BUFFERED,
+	NFSD_IO_DONTCACHE,
+	NFSD_IO_DIRECT,
+};
+
+extern u64 nfsd_io_cache_read __read_mostly;
+extern u64 nfsd_io_cache_write __read_mostly;
+
 extern int nfsd_max_blksize;
 
 static inline int nfsd_v4client(struct svc_rqst *rq)

> [02/13] NFSD: pass nfsd_file to nfsd_iter_read()
>         commit: 63a534c8b18642dc27318e08b77952c4d7f55628
> [03/13] NFSD: add io_cache_read controls to debugfs interface
>         commit: f76b72e4908c556021d94bdeca86fffce430c791
> [04/13] NFSD: add io_cache_write controls to debugfs interface
>         commit: a45da44bb6bade1dfef569c792ae2ee6507f4724

> [06/13] NFSD: issue READs using O_DIRECT even if IO is misaligned
>         commit: 6d80efb3cb6f9817bedfa460e9ddf56a916caf2f

Thanks!
Mike