On Sat, 2025-09-06 at 17:25 -0400, Chuck Lever wrote:
> From: Mike Snitzer <snitzer@xxxxxxxxxx>
>
> Add 'io_cache_read' to NFSD's debugfs interface so that any data
> read by NFSD will either be:
> - cached using page cache (NFSD_IO_BUFFERED=0)
> - cached but removed from the page cache upon completion
> (NFSD_IO_DONTCACHE=1).
>
> io_cache_read may be set by writing to:
> /sys/kernel/debug/nfsd/io_cache_read
>
> Add 'io_cache_write' to NFSD's debugfs interface so that any data
> written by NFSD will either be:
> - cached using page cache (NFSD_IO_BUFFERED=0)
> - cached but removed from the page cache upon completion
> (NFSD_IO_DONTCACHE=1).
>
> io_cache_write may be set by writing to:
> /sys/kernel/debug/nfsd/io_cache_write
>
> The default value for both settings is NFSD_IO_BUFFERED, which is
> NFSD's existing behavior for both read and write. Changes to these
> settings take immediate effect for all exports and NFS versions.
>
> Currently only xfs and ext4 implement RWF_DONTCACHE. For file
> systems that do not implement RWF_DONTCACHE, NFSD use only buffered
> I/O when the io_cache setting is NFSD_IO_DONTCACHE.
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/debugfs.c | 93 +++++++++++++++++++++++++++++++++++++++++++++++
> fs/nfsd/nfsd.h | 9 +++++
> fs/nfsd/vfs.c | 21 +++++++++++
> 3 files changed, 123 insertions(+)
>
> Changes since v1:
> - Corrected patch author
> - Break back to NFSD_IO_BUFFERED when exported file system does not
> support RWF_DONTCACHE
> - Smoke tested NFSD_IO_DONTCACHE with NFSv3,v4.0,v4.1 on xfs and
> tmpfs
>
> diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
> index 84b0c8b559dc..2b1bb716b608 100644
> --- a/fs/nfsd/debugfs.c
> +++ b/fs/nfsd/debugfs.c
> @@ -27,11 +27,98 @@ static int nfsd_dsr_get(void *data, u64 *val)
> static int nfsd_dsr_set(void *data, u64 val)
> {
> nfsd_disable_splice_read = (val > 0) ? true : false;
> + if (!nfsd_disable_splice_read) {
> + /*
> + * Must use buffered I/O if splice_read is enabled.
> + */
> + nfsd_io_cache_read = NFSD_IO_BUFFERED;
> + }
> return 0;
> }
>
> DEFINE_DEBUGFS_ATTRIBUTE(nfsd_dsr_fops, nfsd_dsr_get, nfsd_dsr_set, "%llu\n");
>
> +/*
> + * /sys/kernel/debug/nfsd/io_cache_read
> + *
> + * Contents:
> + * %0: NFS READ will use buffered IO
> + * %1: NFS READ will use dontcache (buffered IO w/ dropbehind)
> + *
> + * This setting takes immediate effect for all NFS versions,
> + * all exports, and in all NFSD net namespaces.
> + */
> +
> +static int nfsd_io_cache_read_get(void *data, u64 *val)
> +{
> + *val = nfsd_io_cache_read;
> + return 0;
> +}
> +
> +static int nfsd_io_cache_read_set(void *data, u64 val)
> +{
> + int ret = 0;
> +
> + switch (val) {
> + case NFSD_IO_BUFFERED:
> + nfsd_io_cache_read = NFSD_IO_BUFFERED;
> + break;
> + case NFSD_IO_DONTCACHE:
> + /*
> + * Must disable splice_read when enabling
> + * NFSD_IO_DONTCACHE.
> + */
> + nfsd_disable_splice_read = true;
> + nfsd_io_cache_read = val;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> +
> + return ret;
> +}
> +
> +DEFINE_DEBUGFS_ATTRIBUTE(nfsd_io_cache_read_fops, nfsd_io_cache_read_get,
> + nfsd_io_cache_read_set, "%llu\n");
> +
> +/*
> + * /sys/kernel/debug/nfsd/io_cache_write
> + *
> + * Contents:
> + * %0: NFS WRITE will use buffered IO
> + * %1: NFS WRITE will use dontcache (buffered IO w/ dropbehind)
> + *
> + * This setting takes immediate effect for all NFS versions,
> + * all exports, and in all NFSD net namespaces.
> + */
> +
> +static int nfsd_io_cache_write_get(void *data, u64 *val)
> +{
> + *val = nfsd_io_cache_write;
> + return 0;
> +}
> +
> +static int nfsd_io_cache_write_set(void *data, u64 val)
> +{
> + int ret = 0;
> +
> + switch (val) {
> + case NFSD_IO_BUFFERED:
> + case NFSD_IO_DONTCACHE:
> + nfsd_io_cache_write = val;
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> +
> + return ret;
> +}
> +
> +DEFINE_DEBUGFS_ATTRIBUTE(nfsd_io_cache_write_fops, nfsd_io_cache_write_get,
> + nfsd_io_cache_write_set, "%llu\n");
> +
> void nfsd_debugfs_exit(void)
> {
> debugfs_remove_recursive(nfsd_top_dir);
> @@ -44,4 +131,10 @@ void nfsd_debugfs_init(void)
>
> debugfs_create_file("disable-splice-read", S_IWUSR | S_IRUGO,
> nfsd_top_dir, NULL, &nfsd_dsr_fops);
> +
> + debugfs_create_file("io_cache_read", 0644, nfsd_top_dir, NULL,
> + &nfsd_io_cache_read_fops);
> +
> + debugfs_create_file("io_cache_write", 0644, nfsd_top_dir, NULL,
> + &nfsd_io_cache_write_fops);
> }
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index 1cd0bed57bc2..809729d41e08 100644
> --- a/fs/nfsd/nfsd.h
> +++ b/fs/nfsd/nfsd.h
> @@ -153,6 +153,15 @@ static inline void nfsd_debugfs_exit(void) {}
>
> extern bool nfsd_disable_splice_read __read_mostly;
>
> +enum {
> + /* Any new NFSD_IO enum value must be added at the end */
> + NFSD_IO_BUFFERED,
> + NFSD_IO_DONTCACHE,
> +};
> +
> +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)
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 3cd3b9e069f4..714777c221ed 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -49,6 +49,8 @@
> #define NFSDDBG_FACILITY NFSDDBG_FILEOP
>
> bool nfsd_disable_splice_read __read_mostly;
> +u64 nfsd_io_cache_read __read_mostly = NFSD_IO_BUFFERED;
> +u64 nfsd_io_cache_write __read_mostly = NFSD_IO_BUFFERED;
>
> /**
> * nfserrno - Map Linux errnos to NFS errnos
> @@ -1099,6 +1101,16 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
> size_t len;
>
> init_sync_kiocb(&kiocb, file);
> +
> + switch (nfsd_io_cache_read) {
> + case NFSD_IO_BUFFERED:
> + break;
> + case NFSD_IO_DONTCACHE:
> + if (file->f_op->fop_flags & FOP_DONTCACHE)
> + kiocb.ki_flags = IOCB_DONTCACHE;
> + break;
> + }
> +
> kiocb.ki_pos = offset;
>
> v = 0;
> @@ -1224,6 +1236,15 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> since = READ_ONCE(file->f_wb_err);
> if (verf)
> nfsd_copy_write_verifier(verf, nn);
> +
> + switch (nfsd_io_cache_write) {
> + case NFSD_IO_BUFFERED:
> + break;
> + case NFSD_IO_DONTCACHE:
> + if (file->f_op->fop_flags & FOP_DONTCACHE)
> + kiocb.ki_flags |= IOCB_DONTCACHE;
> + break;
> + }
> host_err = vfs_iocb_iter_write(file, &kiocb, &iter);
> if (host_err < 0) {
> commit_reset_write_verifier(nn, rqstp, host_err);
Could we get this into v6.18?
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
