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malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2508110000 definitions=main-2509030147 X-Proofpoint-GUID: uAZsMiqh1VmTyWMBtzGIyFv3h7m-P8GY X-Proofpoint-ORIG-GUID: uAZsMiqh1VmTyWMBtzGIyFv3h7m-P8GY X-Authority-Analysis: v=2.4 cv=Of2YDgTY c=1 sm=1 tr=0 ts=68b852fd b=1 cx=c_pps a=WeWmnZmh0fydH62SvGsd2A==:117 a=WeWmnZmh0fydH62SvGsd2A==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=QDtFxmwZSgi6VDxugLkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODMwMDAzMiBTYWx0ZWRfX0dZKWD39A5lk nLa2wMFrKE1UKsdS5JpIauJZlp8UZrOpjAM3PM4rIenzzz9mP0zK6OHzJL23T6H9WLSWEXir6pI 6SmcsrrO4zDqvdP6mjaNQtGVGvKai/CGiqWoo68o4NtFxJeeUh+P6+TRMtHGTtpgS0pkN7EcTcy NAWutcI6lCkRHMhJ0EW7ESFKLkIg8O0UYvcYL8NXwWKSL2AKKLMERoP3ByuzBI1CbMFZaitS+S2 Jvs7vxX5RUOAY0Za/uicVOTjRf9EQ3BF2R/lKmso0/T1U7rTqPdUiOMMhpgpnOKiESFSNqMcd3W KGyUUuBMwKyjtKK1kYsMC0BxofG0GGI+w5MyTkEwyt9S5LejfdcKB1yD8jOIhhQzQ8Klwn+W7Sf ScjdiUdG On 8/26/25 2:57 PM, Mike Snitzer wrote: > 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=1) > - cached but removed from the page cache upon completion > (NFSD_IO_DONTCACHE=2). > - not cached (NFSD_IO_DIRECT=3) > > io_cache_read may be set by writing to: > /sys/kernel/debug/nfsd/io_cache_read > > If NFSD_IO_DONTCACHE is specified using 2, FOP_DONTCACHE must be > advertised as supported by the underlying filesystem (e.g. XFS), > otherwise all IO flagged with RWF_DONTCACHE will fail with > -EOPNOTSUPP. > > If NFSD_IO_DIRECT is specified using 3, the IO must be aligned > relative to the underlying block device's logical_block_size. Also the > memory buffer used to store the read must be aligned relative to the > underlying block device's dma_alignment. > > Signed-off-by: Mike Snitzer > Reviewed-by: Jeff Layton > --- > fs/nfsd/debugfs.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++ > fs/nfsd/nfsd.h | 9 ++++++++ > fs/nfsd/vfs.c | 18 +++++++++++++++ > 3 files changed, 84 insertions(+) > > diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c > index 84b0c8b559dc9..3cadd45868b48 100644 > --- a/fs/nfsd/debugfs.c > +++ b/fs/nfsd/debugfs.c > @@ -27,11 +27,65 @@ 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) { > + /* > + * Cannot use NFSD_IO_DONTCACHE or NFSD_IO_DIRECT > + * 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: > + * %1: NFS READ will use buffered IO > + * %2: NFS READ will use dontcache (buffered IO w/ dropbehind) > + * %3: NFS READ will use direct IO > + * > + * The default value of this setting is zero (UNSPECIFIED). Hi Mike - I can't remember why we have the UNSPECIFIED setting? IME a debug file reflects the current setting, so if our default behavior is "buffered" then the first "cat io_cache_read" should reflect that rather than "I haven't been changed yet". This doesn't seem like the usual semantics of a /sys/kernel/debug file, IME. For example, a user space application may want to read io_cache_read to find out what the current behavior is. If it gets 0 (UNSPECIFIED) then it has found out nothing. However, if there is a good reason to keep UNSPECIFIED, then you need to add a " %0: NFS READ uses the default behavior" to the documenting comment for nfsd_io_cache_{read,write}. My preference is to remove NFSD_IO_UNSPECIFIED from this patch and her sister (4/7). > + * 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: > + case NFSD_IO_DIRECT: > + /* > + * Must disable splice_read when enabling > + * NFSD_IO_DONTCACHE or NFSD_IO_DIRECT. > + */ > + 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"); > + > void nfsd_debugfs_exit(void) > { > debugfs_remove_recursive(nfsd_top_dir); > @@ -44,4 +98,7 @@ 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", S_IWUSR | S_IRUGO, > + nfsd_top_dir, NULL, &nfsd_io_cache_read_fops); > } > diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h > index 1cd0bed57bc2f..6ef799405145f 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 { > + NFSD_IO_UNSPECIFIED = 0, > + NFSD_IO_BUFFERED, > + NFSD_IO_DONTCACHE, > + NFSD_IO_DIRECT, > +}; > + > +extern u64 nfsd_io_cache_read __read_mostly; And then here, initialize nfsd_io_cache_read to reflect the default behavior. That would be NFSD_IO_BUFFERED for now... then later we might want to change it to NFSD_IO_DIRECT, for instance. Same suggestion for 4/7. > + > 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 79439ad93880a..8ea8b80097195 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -49,6 +49,7 @@ > #define NFSDDBG_FACILITY NFSDDBG_FILEOP > > bool nfsd_disable_splice_read __read_mostly; > +u64 nfsd_io_cache_read __read_mostly; > > /** > * nfserrno - Map Linux errnos to NFS errnos > @@ -1099,6 +1100,23 @@ __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_DIRECT: > + /* Verify ondisk and memory DIO alignment */ > + if (nf->nf_dio_mem_align && nf->nf_dio_read_offset_align && > + (((offset | *count) & (nf->nf_dio_read_offset_align - 1)) == 0) && > + (base & (nf->nf_dio_mem_align - 1)) == 0) > + kiocb.ki_flags = IOCB_DIRECT; > + break; > + case NFSD_IO_DONTCACHE: > + kiocb.ki_flags = IOCB_DONTCACHE; > + fallthrough; Nit: Make this "break;". This is brittle: if someone adds something to the NFSD_IO_BUFFERED arm but happens to miss that the DONTCACHE arm above it is "fallthrough" then we have a latent bug. Same suggestion for 4/7. > + case NFSD_IO_UNSPECIFIED: > + case NFSD_IO_BUFFERED: > + break; > + } > + > kiocb.ki_pos = offset; > > v = 0; -- Chuck Lever