* [PATCH v3 1/4] NFSD: refactor nfsd_read_vector_dio to EVENT_CLASS useful for READ and WRITE
2025-07-31 23:06 [PATCH v3 0/4] NFSD DIRECT: add handling for misaligned WRITEs Mike Snitzer
@ 2025-07-31 23:06 ` Mike Snitzer
2025-07-31 23:06 ` [PATCH v3 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs Mike Snitzer
` (2 subsequent siblings)
3 siblings, 0 replies; 9+ messages in thread
From: Mike Snitzer @ 2025-07-31 23:06 UTC (permalink / raw)
To: Chuck Lever, Jeff Layton; +Cc: linux-nfs
Transform nfsd_read_vector_dio trace event into nfsd_analyze_dio_class
and use it to create nfsd_analyze_read_dio and nfsd_analyze_write_dio
trace events.
This prepares for nfsd_vfs_write() to also make use of it when
handling misaligned WRITEs.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
---
fs/nfsd/trace.h | 52 ++++++++++++++++++++++++++++++++++++-------------
fs/nfsd/vfs.c | 11 ++++++-----
2 files changed, 44 insertions(+), 19 deletions(-)
diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index 55055482f8a84..4173bd9344b6b 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -473,25 +473,29 @@ DEFINE_NFSD_IO_EVENT(write_done);
DEFINE_NFSD_IO_EVENT(commit_start);
DEFINE_NFSD_IO_EVENT(commit_done);
-TRACE_EVENT(nfsd_read_vector_dio,
+DECLARE_EVENT_CLASS(nfsd_analyze_dio_class,
TP_PROTO(struct svc_rqst *rqstp,
struct svc_fh *fhp,
u64 offset,
u32 len,
- loff_t start,
- loff_t start_extra,
- loff_t end,
- loff_t end_extra),
- TP_ARGS(rqstp, fhp, offset, len, start, start_extra, end, end_extra),
+ loff_t start,
+ ssize_t start_len,
+ loff_t middle,
+ ssize_t middle_len,
+ loff_t end,
+ ssize_t end_len),
+ TP_ARGS(rqstp, fhp, offset, len, start, start_len, middle, middle_len, end, end_len),
TP_STRUCT__entry(
__field(u32, xid)
__field(u32, fh_hash)
__field(u64, offset)
__field(u32, len)
__field(loff_t, start)
- __field(loff_t, start_extra)
+ __field(ssize_t, start_len)
+ __field(loff_t, middle)
+ __field(ssize_t, middle_len)
__field(loff_t, end)
- __field(loff_t, end_extra)
+ __field(ssize_t, end_len)
),
TP_fast_assign(
__entry->xid = be32_to_cpu(rqstp->rq_xid);
@@ -499,16 +503,36 @@ TRACE_EVENT(nfsd_read_vector_dio,
__entry->offset = offset;
__entry->len = len;
__entry->start = start;
- __entry->start_extra = start_extra;
+ __entry->start_len = start_len;
+ __entry->middle = middle;
+ __entry->middle_len = middle_len;
__entry->end = end;
- __entry->end_extra = end_extra;
+ __entry->end_len = end_len;
),
- TP_printk("xid=0x%08x fh_hash=0x%08x offset=%llu len=%u start=%llu+%llu end=%llu-%llu",
+ TP_printk("xid=0x%08x fh_hash=0x%08x offset=%llu len=%u start=%llu+%lu middle=%llu+%lu end=%llu+%lu",
__entry->xid, __entry->fh_hash,
__entry->offset, __entry->len,
- __entry->start, __entry->start_extra,
- __entry->end, __entry->end_extra)
-);
+ __entry->start, __entry->start_len,
+ __entry->middle, __entry->middle_len,
+ __entry->end, __entry->end_len)
+)
+
+#define DEFINE_NFSD_ANALYZE_DIO_EVENT(name) \
+DEFINE_EVENT(nfsd_analyze_dio_class, nfsd_analyze_##name##_dio, \
+ TP_PROTO(struct svc_rqst *rqstp, \
+ struct svc_fh *fhp, \
+ u64 offset, \
+ u32 len, \
+ loff_t start, \
+ ssize_t start_len, \
+ loff_t middle, \
+ ssize_t middle_len, \
+ loff_t end, \
+ ssize_t end_len), \
+ TP_ARGS(rqstp, fhp, offset, len, start, start_len, middle, middle_len, end, end_len))
+
+DEFINE_NFSD_ANALYZE_DIO_EVENT(read);
+DEFINE_NFSD_ANALYZE_DIO_EVENT(write);
DECLARE_EVENT_CLASS(nfsd_err_class,
TP_PROTO(struct svc_rqst *rqstp,
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 46189020172fb..35c29b8ade9c3 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1094,7 +1094,7 @@ static bool nfsd_analyze_read_dio(struct svc_rqst *rqstp, struct svc_fh *fhp,
struct nfsd_read_dio *read_dio)
{
const u32 dio_blocksize = nf->nf_dio_read_offset_align;
- loff_t orig_end = offset + len;
+ loff_t middle_end, orig_end = offset + len;
if (WARN_ONCE(!nf->nf_dio_mem_align || !nf->nf_dio_read_offset_align,
"%s: underlying filesystem has not provided DIO alignment info\n",
@@ -1133,10 +1133,11 @@ static bool nfsd_analyze_read_dio(struct svc_rqst *rqstp, struct svc_fh *fhp,
}
/* Show original offset and count, and how it was expanded for DIO */
- trace_nfsd_read_vector_dio(rqstp, fhp, offset, len,
- read_dio->start, read_dio->start_extra,
- read_dio->end, read_dio->end_extra);
-
+ middle_end = read_dio->end - read_dio->end_extra;
+ trace_nfsd_analyze_read_dio(rqstp, fhp, offset, len,
+ read_dio->start, read_dio->start_extra,
+ offset, (middle_end - offset),
+ middle_end, read_dio->end_extra);
return true;
}
--
2.44.0
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH v3 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs
2025-07-31 23:06 [PATCH v3 0/4] NFSD DIRECT: add handling for misaligned WRITEs Mike Snitzer
2025-07-31 23:06 ` [PATCH v3 1/4] NFSD: refactor nfsd_read_vector_dio to EVENT_CLASS useful for READ and WRITE Mike Snitzer
@ 2025-07-31 23:06 ` Mike Snitzer
2025-08-01 20:52 ` Chuck Lever
2025-07-31 23:06 ` [PATCH v3 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned Mike Snitzer
2025-07-31 23:06 ` [PATCH v3 4/4] NFSD: handle unaligned DIO for NFS reexport Mike Snitzer
3 siblings, 1 reply; 9+ messages in thread
From: Mike Snitzer @ 2025-07-31 23:06 UTC (permalink / raw)
To: Chuck Lever, Jeff Layton; +Cc: linux-nfs
Refactor nfsd_vfs_write() to support splitting a WRITE into parts
(which will be either misaligned or DIO-aligned). Doing so in a
preliminary commit just allows for indentation and slight
transformation to be more easily understood and reviewed.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
---
fs/nfsd/vfs.c | 45 +++++++++++++++++++++++++++------------------
1 file changed, 27 insertions(+), 18 deletions(-)
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 35c29b8ade9c3..edac73349da0f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1341,7 +1341,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
struct super_block *sb = file_inode(file)->i_sb;
struct kiocb kiocb;
struct svc_export *exp;
- struct iov_iter iter;
errseq_t since;
__be32 nfserr;
int host_err;
@@ -1349,6 +1348,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
unsigned int pflags = current->flags;
bool restore_flags = false;
unsigned int nvecs;
+ struct iov_iter iter_stack[1];
+ struct iov_iter *iter = iter_stack;
+ unsigned int n_iters = 0;
trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
@@ -1378,14 +1380,15 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
kiocb.ki_flags |= IOCB_DSYNC;
nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
- iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
+ iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
+ n_iters++;
switch (nfsd_io_cache_write) {
case NFSD_IO_DIRECT:
/* direct I/O must be aligned to device logical sector size */
if (nf->nf_dio_mem_align && nf->nf_dio_offset_align &&
(((offset | *cnt) & (nf->nf_dio_offset_align-1)) == 0) &&
- iov_iter_is_aligned(&iter, nf->nf_dio_mem_align - 1,
+ iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1,
nf->nf_dio_offset_align - 1))
kiocb.ki_flags = IOCB_DIRECT;
break;
@@ -1399,22 +1402,28 @@ 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);
- host_err = vfs_iocb_iter_write(file, &kiocb, &iter);
- if (host_err < 0) {
- commit_reset_write_verifier(nn, rqstp, host_err);
- goto out_nfserr;
- }
- *cnt = host_err;
- nfsd_stats_io_write_add(nn, exp, *cnt);
- fsnotify_modify(file);
- host_err = filemap_check_wb_err(file->f_mapping, since);
- if (host_err < 0)
- goto out_nfserr;
-
- if (stable && fhp->fh_use_wgather) {
- host_err = wait_for_concurrent_writes(file);
- if (host_err < 0)
+ *cnt = 0;
+ for (int i = 0; i < n_iters; i++) {
+ host_err = vfs_iocb_iter_write(file, &kiocb, &iter[i]);
+ if (host_err < 0) {
commit_reset_write_verifier(nn, rqstp, host_err);
+ goto out_nfserr;
+ }
+ *cnt += host_err;
+ nfsd_stats_io_write_add(nn, exp, host_err);
+
+ fsnotify_modify(file);
+ host_err = filemap_check_wb_err(file->f_mapping, since);
+ if (host_err < 0)
+ goto out_nfserr;
+
+ if (stable && fhp->fh_use_wgather) {
+ host_err = wait_for_concurrent_writes(file);
+ if (host_err < 0) {
+ commit_reset_write_verifier(nn, rqstp, host_err);
+ goto out_nfserr;
+ }
+ }
}
out_nfserr:
--
2.44.0
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH v3 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs
2025-07-31 23:06 ` [PATCH v3 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs Mike Snitzer
@ 2025-08-01 20:52 ` Chuck Lever
2025-08-01 22:29 ` Mike Snitzer
0 siblings, 1 reply; 9+ messages in thread
From: Chuck Lever @ 2025-08-01 20:52 UTC (permalink / raw)
To: Mike Snitzer; +Cc: linux-nfs, Jeff Layton
On 7/31/25 7:06 PM, Mike Snitzer wrote:
> Refactor nfsd_vfs_write() to support splitting a WRITE into parts
> (which will be either misaligned or DIO-aligned). Doing so in a
> preliminary commit just allows for indentation and slight
> transformation to be more easily understood and reviewed.
>
> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> ---
> fs/nfsd/vfs.c | 45 +++++++++++++++++++++++++++------------------
> 1 file changed, 27 insertions(+), 18 deletions(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 35c29b8ade9c3..edac73349da0f 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1341,7 +1341,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> struct super_block *sb = file_inode(file)->i_sb;
> struct kiocb kiocb;
> struct svc_export *exp;
> - struct iov_iter iter;
> errseq_t since;
> __be32 nfserr;
> int host_err;
> @@ -1349,6 +1348,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> unsigned int pflags = current->flags;
> bool restore_flags = false;
> unsigned int nvecs;
> + struct iov_iter iter_stack[1];
> + struct iov_iter *iter = iter_stack;
> + unsigned int n_iters = 0;
>
> trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
>
> @@ -1378,14 +1380,15 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> kiocb.ki_flags |= IOCB_DSYNC;
>
> nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
> - iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
> + iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
> + n_iters++;
>
> switch (nfsd_io_cache_write) {
> case NFSD_IO_DIRECT:
> /* direct I/O must be aligned to device logical sector size */
> if (nf->nf_dio_mem_align && nf->nf_dio_offset_align &&
> (((offset | *cnt) & (nf->nf_dio_offset_align-1)) == 0) &&
> - iov_iter_is_aligned(&iter, nf->nf_dio_mem_align - 1,
> + iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1,
> nf->nf_dio_offset_align - 1))
> kiocb.ki_flags = IOCB_DIRECT;
> break;
> @@ -1399,22 +1402,28 @@ 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);
> - host_err = vfs_iocb_iter_write(file, &kiocb, &iter);
> - if (host_err < 0) {
> - commit_reset_write_verifier(nn, rqstp, host_err);
> - goto out_nfserr;
> - }
> - *cnt = host_err;
> - nfsd_stats_io_write_add(nn, exp, *cnt);
> - fsnotify_modify(file);
> - host_err = filemap_check_wb_err(file->f_mapping, since);
> - if (host_err < 0)
> - goto out_nfserr;
> -
> - if (stable && fhp->fh_use_wgather) {
> - host_err = wait_for_concurrent_writes(file);
> - if (host_err < 0)
> + *cnt = 0;
> + for (int i = 0; i < n_iters; i++) {
> + host_err = vfs_iocb_iter_write(file, &kiocb, &iter[i]);
> + if (host_err < 0) {
> commit_reset_write_verifier(nn, rqstp, host_err);
> + goto out_nfserr;
> + }
Does this loop wait after each iter is written? Would it be better to
wait once after all the iters have been written?
> + *cnt += host_err;
> + nfsd_stats_io_write_add(nn, exp, host_err);
> +
> + fsnotify_modify(file);
> + host_err = filemap_check_wb_err(file->f_mapping, since);
> + if (host_err < 0)
> + goto out_nfserr;
> +
> + if (stable && fhp->fh_use_wgather) {
> + host_err = wait_for_concurrent_writes(file);
> + if (host_err < 0) {
> + commit_reset_write_verifier(nn, rqstp, host_err);
> + goto out_nfserr;
> + }
> + }
> }
>
> out_nfserr:
--
Chuck Lever
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs
2025-08-01 20:52 ` Chuck Lever
@ 2025-08-01 22:29 ` Mike Snitzer
0 siblings, 0 replies; 9+ messages in thread
From: Mike Snitzer @ 2025-08-01 22:29 UTC (permalink / raw)
To: Chuck Lever; +Cc: linux-nfs, Jeff Layton
On Fri, Aug 01, 2025 at 04:52:38PM -0400, Chuck Lever wrote:
> On 7/31/25 7:06 PM, Mike Snitzer wrote:
> > Refactor nfsd_vfs_write() to support splitting a WRITE into parts
> > (which will be either misaligned or DIO-aligned). Doing so in a
> > preliminary commit just allows for indentation and slight
> > transformation to be more easily understood and reviewed.
> >
> > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > Reviewed-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/nfsd/vfs.c | 45 +++++++++++++++++++++++++++------------------
> > 1 file changed, 27 insertions(+), 18 deletions(-)
> >
> > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > index 35c29b8ade9c3..edac73349da0f 100644
> > --- a/fs/nfsd/vfs.c
> > +++ b/fs/nfsd/vfs.c
> > @@ -1341,7 +1341,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > struct super_block *sb = file_inode(file)->i_sb;
> > struct kiocb kiocb;
> > struct svc_export *exp;
> > - struct iov_iter iter;
> > errseq_t since;
> > __be32 nfserr;
> > int host_err;
> > @@ -1349,6 +1348,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > unsigned int pflags = current->flags;
> > bool restore_flags = false;
> > unsigned int nvecs;
> > + struct iov_iter iter_stack[1];
> > + struct iov_iter *iter = iter_stack;
> > + unsigned int n_iters = 0;
> >
> > trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
> >
> > @@ -1378,14 +1380,15 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > kiocb.ki_flags |= IOCB_DSYNC;
> >
> > nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
> > - iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
> > + iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
> > + n_iters++;
> >
> > switch (nfsd_io_cache_write) {
> > case NFSD_IO_DIRECT:
> > /* direct I/O must be aligned to device logical sector size */
> > if (nf->nf_dio_mem_align && nf->nf_dio_offset_align &&
> > (((offset | *cnt) & (nf->nf_dio_offset_align-1)) == 0) &&
> > - iov_iter_is_aligned(&iter, nf->nf_dio_mem_align - 1,
> > + iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1,
> > nf->nf_dio_offset_align - 1))
> > kiocb.ki_flags = IOCB_DIRECT;
> > break;
> > @@ -1399,22 +1402,28 @@ 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);
> > - host_err = vfs_iocb_iter_write(file, &kiocb, &iter);
> > - if (host_err < 0) {
> > - commit_reset_write_verifier(nn, rqstp, host_err);
> > - goto out_nfserr;
> > - }
> > - *cnt = host_err;
> > - nfsd_stats_io_write_add(nn, exp, *cnt);
> > - fsnotify_modify(file);
> > - host_err = filemap_check_wb_err(file->f_mapping, since);
> > - if (host_err < 0)
> > - goto out_nfserr;
> > -
> > - if (stable && fhp->fh_use_wgather) {
> > - host_err = wait_for_concurrent_writes(file);
> > - if (host_err < 0)
> > + *cnt = 0;
> > + for (int i = 0; i < n_iters; i++) {
> > + host_err = vfs_iocb_iter_write(file, &kiocb, &iter[i]);
> > + if (host_err < 0) {
> > commit_reset_write_verifier(nn, rqstp, host_err);
> > + goto out_nfserr;
> > + }
>
> Does this loop wait after each iter is written? Would it be better to
> wait once after all the iters have been written?
It does, sorry about that. This incremental fixes it up and is easily
folded into this patch:
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 2eabcb5651ba..1590fc1fb420 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1533,19 +1533,17 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
}
*cnt += host_err;
nfsd_stats_io_write_add(nn, exp, host_err);
+ }
- fsnotify_modify(file);
- host_err = filemap_check_wb_err(file->f_mapping, since);
+ fsnotify_modify(file);
+ host_err = filemap_check_wb_err(file->f_mapping, since);
+ if (host_err < 0)
+ goto out_nfserr;
+
+ if (stable && fhp->fh_use_wgather) {
+ host_err = wait_for_concurrent_writes(file);
if (host_err < 0)
- goto out_nfserr;
-
- if (stable && fhp->fh_use_wgather) {
- host_err = wait_for_concurrent_writes(file);
- if (host_err < 0) {
- commit_reset_write_verifier(nn, rqstp, host_err);
- goto out_nfserr;
- }
- }
+ commit_reset_write_verifier(nn, rqstp, host_err);
}
out_nfserr:
^ permalink raw reply related [flat|nested] 9+ messages in thread
* [PATCH v3 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned
2025-07-31 23:06 [PATCH v3 0/4] NFSD DIRECT: add handling for misaligned WRITEs Mike Snitzer
2025-07-31 23:06 ` [PATCH v3 1/4] NFSD: refactor nfsd_read_vector_dio to EVENT_CLASS useful for READ and WRITE Mike Snitzer
2025-07-31 23:06 ` [PATCH v3 2/4] NFSD: prepare nfsd_vfs_write() to use O_DIRECT on misaligned WRITEs Mike Snitzer
@ 2025-07-31 23:06 ` Mike Snitzer
2025-08-05 14:55 ` Chuck Lever
2025-07-31 23:06 ` [PATCH v3 4/4] NFSD: handle unaligned DIO for NFS reexport Mike Snitzer
3 siblings, 1 reply; 9+ messages in thread
From: Mike Snitzer @ 2025-07-31 23:06 UTC (permalink / raw)
To: Chuck Lever, Jeff Layton; +Cc: linux-nfs
If NFSD_IO_DIRECT is used, split any misaligned WRITE into a start,
middle and end as needed. The large middle extent is DIO-aligned and
the start and/or end are misaligned. Buffered IO is used for the
misaligned extents and O_DIRECT is used for the middle DIO-aligned
extent.
The nfsd_analyze_write_dio trace event shows how NFSD splits a given
misaligned WRITE into a mix of misaligned extent(s) and a DIO-aligned
extent.
This combination of trace events is useful:
echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_opened/enable
echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_analyze_write_dio/enable
echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_io_done/enable
echo 1 > /sys/kernel/tracing/events/xfs/xfs_file_direct_write/enable
Which for this dd command:
dd if=/dev/zero of=/mnt/share1/test bs=47008 count=2 oflag=direct
Results in:
nfsd-55714 [043] ..... 79976.260851: nfsd_write_opened: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008
nfsd-55714 [043] ..... 79976.260852: nfsd_analyze_write_dio: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008 start=0+0 middle=0+45056 end=45056+1952
nfsd-55714 [043] ..... 79976.260857: xfs_file_direct_write: dev 259:12 ino 0x3e00008f disize 0x0 pos 0x0 bytecount 0xb000
nfsd-55714 [043] ..... 79976.260965: nfsd_write_io_done: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008
nfsd-55714 [043] ..... 79976.307762: nfsd_write_opened: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008
nfsd-55714 [043] ..... 79976.307762: nfsd_analyze_write_dio: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008 start=47008+2144 middle=49152+40960 end=90112+3904
nfsd-55714 [043] ..... 79976.307797: xfs_file_direct_write: dev 259:12 ino 0x3e00008f disize 0xc000 pos 0xc000 bytecount 0xa000
nfsd-55714 [043] ..... 79976.307866: nfsd_write_io_done: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
---
fs/nfsd/vfs.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 124 insertions(+), 11 deletions(-)
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index edac73349da0f..f0cfd7b457240 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1314,6 +1314,113 @@ static int wait_for_concurrent_writes(struct file *file)
return err;
}
+struct nfsd_write_dio
+{
+ loff_t middle_offset; /* Offset for start of DIO-aligned middle */
+ loff_t end_offset; /* Offset for start of DIO-aligned end */
+ ssize_t start_len; /* Length for misaligned first extent */
+ ssize_t middle_len; /* Length for DIO-aligned middle extent */
+ ssize_t end_len; /* Length for misaligned last extent */
+};
+
+static void init_nfsd_write_dio(struct nfsd_write_dio *write_dio)
+{
+ memset(write_dio, 0, sizeof(*write_dio));
+}
+
+static bool nfsd_analyze_write_dio(struct svc_rqst *rqstp, struct svc_fh *fhp,
+ struct nfsd_file *nf, loff_t offset,
+ unsigned long len, struct nfsd_write_dio *write_dio)
+{
+ const u32 dio_blocksize = nf->nf_dio_offset_align;
+ loff_t orig_end, middle_end, start_end, start_offset = offset;
+ ssize_t start_len = len;
+ bool aligned = true;
+
+ if (WARN_ONCE(!nf->nf_dio_mem_align || !dio_blocksize,
+ "%s: underlying filesystem has not provided DIO alignment info\n",
+ __func__))
+ return false;
+
+ if (WARN_ONCE(dio_blocksize > PAGE_SIZE,
+ "%s: underlying storage's dio_blocksize=%u > PAGE_SIZE=%lu\n",
+ __func__, dio_blocksize, PAGE_SIZE))
+ return false;
+
+ if (unlikely(len < dio_blocksize)) {
+ aligned = false;
+ goto out;
+ }
+
+ if (((offset | len) & (dio_blocksize-1)) == 0) {
+ /* already DIO-aligned, no misaligned head or tail */
+ write_dio->middle_offset = offset;
+ write_dio->middle_len = len;
+ /* clear these for the benefit of trace_nfsd_analyze_write_dio */
+ start_offset = 0;
+ start_len = 0;
+ goto out;
+ }
+
+ start_end = round_up(offset, dio_blocksize);
+ start_len = start_end - offset;
+ orig_end = offset + len;
+ middle_end = round_down(orig_end, dio_blocksize);
+
+ write_dio->start_len = start_len;
+ write_dio->middle_offset = start_end;
+ write_dio->middle_len = middle_end - start_end;
+ write_dio->end_offset = middle_end;
+ write_dio->end_len = orig_end - middle_end;
+out:
+ trace_nfsd_analyze_write_dio(rqstp, fhp, offset, len, start_offset, start_len,
+ write_dio->middle_offset, write_dio->middle_len,
+ write_dio->end_offset, write_dio->end_len);
+ return aligned;
+}
+
+/*
+ * Setup as many as 3 iov_iter based on extents possibly described by @write_dio.
+ * @iterp: pointer to pointer to onstack array of 3 iov_iter structs from caller.
+ * @rq_bvec: backing bio_vec used to setup all 3 iov_iter permutations.
+ * @nvecs: number of segments in @rq_bvec
+ * @cnt: size of the request in bytes
+ * @write_dio: nfsd_write_dio struct that describes start, middle and end extents.
+ *
+ * Returns the number of iov_iter that were setup.
+ */
+static int nfsd_setup_write_iters(struct iov_iter **iterp, struct bio_vec *rq_bvec,
+ unsigned int nvecs, unsigned long cnt,
+ struct nfsd_write_dio *write_dio)
+{
+ int n_iters = 0;
+ struct iov_iter *iters = *iterp;
+
+ /* Setup misaligned start? */
+ if (write_dio->start_len) {
+ iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt);
+ iters[n_iters].count = write_dio->start_len;
+ n_iters++;
+ }
+
+ /* Setup possibly DIO-aligned middle */
+ iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt);
+ if (write_dio->start_len)
+ iov_iter_advance(&iters[n_iters], write_dio->start_len);
+ iters[n_iters].count -= write_dio->end_len;
+ n_iters++;
+
+ /* Setup misaligned end? */
+ if (write_dio->end_len) {
+ iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt);
+ iov_iter_advance(&iters[n_iters],
+ write_dio->start_len + write_dio->middle_len);
+ n_iters++;
+ }
+
+ return n_iters;
+}
+
/**
* nfsd_vfs_write - write data to an already-open file
* @rqstp: RPC execution context
@@ -1348,9 +1455,11 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
unsigned int pflags = current->flags;
bool restore_flags = false;
unsigned int nvecs;
- struct iov_iter iter_stack[1];
+ struct iov_iter iter_stack[3];
struct iov_iter *iter = iter_stack;
unsigned int n_iters = 0;
+ bool dio_aligned = false;
+ struct nfsd_write_dio write_dio;
trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
@@ -1379,18 +1488,12 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
if (stable && !fhp->fh_use_wgather)
kiocb.ki_flags |= IOCB_DSYNC;
- nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
- iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
- n_iters++;
-
+ init_nfsd_write_dio(&write_dio);
switch (nfsd_io_cache_write) {
case NFSD_IO_DIRECT:
- /* direct I/O must be aligned to device logical sector size */
- if (nf->nf_dio_mem_align && nf->nf_dio_offset_align &&
- (((offset | *cnt) & (nf->nf_dio_offset_align-1)) == 0) &&
- iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1,
- nf->nf_dio_offset_align - 1))
- kiocb.ki_flags = IOCB_DIRECT;
+ if (nfsd_analyze_write_dio(rqstp, fhp, nf, offset,
+ *cnt, &write_dio))
+ dio_aligned = true;
break;
case NFSD_IO_DONTCACHE:
kiocb.ki_flags = IOCB_DONTCACHE;
@@ -1399,11 +1502,21 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
break;
}
+ nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
+ n_iters = nfsd_setup_write_iters(&iter, rqstp->rq_bvec, nvecs, *cnt, &write_dio);
+
since = READ_ONCE(file->f_wb_err);
if (verf)
nfsd_copy_write_verifier(verf, nn);
*cnt = 0;
for (int i = 0; i < n_iters; i++) {
+ if (dio_aligned) {
+ if (iov_iter_is_aligned(&iter[i], nf->nf_dio_mem_align - 1,
+ nf->nf_dio_offset_align - 1))
+ kiocb.ki_flags |= IOCB_DIRECT;
+ else
+ kiocb.ki_flags &= ~IOCB_DIRECT;
+ }
host_err = vfs_iocb_iter_write(file, &kiocb, &iter[i]);
if (host_err < 0) {
commit_reset_write_verifier(nn, rqstp, host_err);
--
2.44.0
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH v3 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned
2025-07-31 23:06 ` [PATCH v3 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned Mike Snitzer
@ 2025-08-05 14:55 ` Chuck Lever
2025-08-05 19:02 ` Mike Snitzer
0 siblings, 1 reply; 9+ messages in thread
From: Chuck Lever @ 2025-08-05 14:55 UTC (permalink / raw)
To: Mike Snitzer, Jeff Layton; +Cc: linux-nfs
On 7/31/25 7:06 PM, Mike Snitzer wrote:
> If NFSD_IO_DIRECT is used, split any misaligned WRITE into a start,
> middle and end as needed. The large middle extent is DIO-aligned and
> the start and/or end are misaligned. Buffered IO is used for the
> misaligned extents and O_DIRECT is used for the middle DIO-aligned
> extent.
>
> The nfsd_analyze_write_dio trace event shows how NFSD splits a given
> misaligned WRITE into a mix of misaligned extent(s) and a DIO-aligned
> extent.
>
> This combination of trace events is useful:
>
> echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_opened/enable
> echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_analyze_write_dio/enable
> echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_io_done/enable
> echo 1 > /sys/kernel/tracing/events/xfs/xfs_file_direct_write/enable
>
> Which for this dd command:
>
> dd if=/dev/zero of=/mnt/share1/test bs=47008 count=2 oflag=direct
>
> Results in:
>
> nfsd-55714 [043] ..... 79976.260851: nfsd_write_opened: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008
> nfsd-55714 [043] ..... 79976.260852: nfsd_analyze_write_dio: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008 start=0+0 middle=0+45056 end=45056+1952
> nfsd-55714 [043] ..... 79976.260857: xfs_file_direct_write: dev 259:12 ino 0x3e00008f disize 0x0 pos 0x0 bytecount 0xb000
> nfsd-55714 [043] ..... 79976.260965: nfsd_write_io_done: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008
>
> nfsd-55714 [043] ..... 79976.307762: nfsd_write_opened: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008
> nfsd-55714 [043] ..... 79976.307762: nfsd_analyze_write_dio: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008 start=47008+2144 middle=49152+40960 end=90112+3904
> nfsd-55714 [043] ..... 79976.307797: xfs_file_direct_write: dev 259:12 ino 0x3e00008f disize 0xc000 pos 0xc000 bytecount 0xa000
> nfsd-55714 [043] ..... 79976.307866: nfsd_write_io_done: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008
>
> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> ---
> fs/nfsd/vfs.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 124 insertions(+), 11 deletions(-)
The diffstat tells a worrying story.
For the READ path, nfsd_iter_read() is the fallback -- the hot path
right now is splice reads. So adding instruction path length in
nfsd_iter_read() is a concern, but it's not an immediate problem.
For the write side, there is only one path, which is ballooning with
this set of patches. This is bound to have an impact on page cache
writes, which are still the default write I/O mode.
This is why I'm hesitant to apply this series as it is currently.
If I might suggest a possible action/recourse: Perhaps the patches can
be restructured so that the default cached write mechanism retains a
short IPL. We can leave the de-duplication and other optimizations until
we have field results from our experiments.
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index edac73349da0f..f0cfd7b457240 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1314,6 +1314,113 @@ static int wait_for_concurrent_writes(struct file *file)
> return err;
> }
>
> +struct nfsd_write_dio
> +{
Nit: checkpatch complained about the style of the struct definition. It
prefers
struct nfsd_write_dio {
Same problem in the read-side patches, which I fixed as they were
applied.
> + loff_t middle_offset; /* Offset for start of DIO-aligned middle */
> + loff_t end_offset; /* Offset for start of DIO-aligned end */
> + ssize_t start_len; /* Length for misaligned first extent */
> + ssize_t middle_len; /* Length for DIO-aligned middle extent */
> + ssize_t end_len; /* Length for misaligned last extent */
> +};
> +
> +static void init_nfsd_write_dio(struct nfsd_write_dio *write_dio)
> +{
> + memset(write_dio, 0, sizeof(*write_dio));
> +}
> +
> +static bool nfsd_analyze_write_dio(struct svc_rqst *rqstp, struct svc_fh *fhp,
> + struct nfsd_file *nf, loff_t offset,
> + unsigned long len, struct nfsd_write_dio *write_dio)
> +{
> + const u32 dio_blocksize = nf->nf_dio_offset_align;
> + loff_t orig_end, middle_end, start_end, start_offset = offset;
> + ssize_t start_len = len;
> + bool aligned = true;
> +
> + if (WARN_ONCE(!nf->nf_dio_mem_align || !dio_blocksize,
> + "%s: underlying filesystem has not provided DIO alignment info\n",
> + __func__))
> + return false;
> +
> + if (WARN_ONCE(dio_blocksize > PAGE_SIZE,
> + "%s: underlying storage's dio_blocksize=%u > PAGE_SIZE=%lu\n",
> + __func__, dio_blocksize, PAGE_SIZE))
> + return false;
> +
> + if (unlikely(len < dio_blocksize)) {
> + aligned = false;
> + goto out;
> + }
> +
> + if (((offset | len) & (dio_blocksize-1)) == 0) {
> + /* already DIO-aligned, no misaligned head or tail */
> + write_dio->middle_offset = offset;
> + write_dio->middle_len = len;
> + /* clear these for the benefit of trace_nfsd_analyze_write_dio */
> + start_offset = 0;
> + start_len = 0;
> + goto out;
> + }
> +
> + start_end = round_up(offset, dio_blocksize);
> + start_len = start_end - offset;
> + orig_end = offset + len;
> + middle_end = round_down(orig_end, dio_blocksize);
> +
> + write_dio->start_len = start_len;
> + write_dio->middle_offset = start_end;
> + write_dio->middle_len = middle_end - start_end;
> + write_dio->end_offset = middle_end;
> + write_dio->end_len = orig_end - middle_end;
> +out:
> + trace_nfsd_analyze_write_dio(rqstp, fhp, offset, len, start_offset, start_len,
> + write_dio->middle_offset, write_dio->middle_len,
> + write_dio->end_offset, write_dio->end_len);
> + return aligned;
> +}
> +
> +/*
> + * Setup as many as 3 iov_iter based on extents possibly described by @write_dio.
> + * @iterp: pointer to pointer to onstack array of 3 iov_iter structs from caller.
> + * @rq_bvec: backing bio_vec used to setup all 3 iov_iter permutations.
> + * @nvecs: number of segments in @rq_bvec
> + * @cnt: size of the request in bytes
> + * @write_dio: nfsd_write_dio struct that describes start, middle and end extents.
> + *
> + * Returns the number of iov_iter that were setup.
> + */
> +static int nfsd_setup_write_iters(struct iov_iter **iterp, struct bio_vec *rq_bvec,
> + unsigned int nvecs, unsigned long cnt,
> + struct nfsd_write_dio *write_dio)
> +{
> + int n_iters = 0;
> + struct iov_iter *iters = *iterp;
> +
> + /* Setup misaligned start? */
> + if (write_dio->start_len) {
> + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt);
> + iters[n_iters].count = write_dio->start_len;
> + n_iters++;
> + }
> +
> + /* Setup possibly DIO-aligned middle */
> + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt);
> + if (write_dio->start_len)
> + iov_iter_advance(&iters[n_iters], write_dio->start_len);
> + iters[n_iters].count -= write_dio->end_len;
> + n_iters++;
> +
> + /* Setup misaligned end? */
> + if (write_dio->end_len) {
> + iov_iter_bvec(&iters[n_iters], ITER_SOURCE, rq_bvec, nvecs, cnt);
> + iov_iter_advance(&iters[n_iters],
> + write_dio->start_len + write_dio->middle_len);
> + n_iters++;
> + }
> +
> + return n_iters;
> +}
> +
> /**
> * nfsd_vfs_write - write data to an already-open file
> * @rqstp: RPC execution context
> @@ -1348,9 +1455,11 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> unsigned int pflags = current->flags;
> bool restore_flags = false;
> unsigned int nvecs;
> - struct iov_iter iter_stack[1];
> + struct iov_iter iter_stack[3];
> struct iov_iter *iter = iter_stack;
> unsigned int n_iters = 0;
> + bool dio_aligned = false;
> + struct nfsd_write_dio write_dio;
>
> trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
>
> @@ -1379,18 +1488,12 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> if (stable && !fhp->fh_use_wgather)
> kiocb.ki_flags |= IOCB_DSYNC;
>
> - nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
> - iov_iter_bvec(&iter[0], ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt);
> - n_iters++;
> -
> + init_nfsd_write_dio(&write_dio);
> switch (nfsd_io_cache_write) {
> case NFSD_IO_DIRECT:
> - /* direct I/O must be aligned to device logical sector size */
> - if (nf->nf_dio_mem_align && nf->nf_dio_offset_align &&
> - (((offset | *cnt) & (nf->nf_dio_offset_align-1)) == 0) &&
> - iov_iter_is_aligned(&iter[0], nf->nf_dio_mem_align - 1,
> - nf->nf_dio_offset_align - 1))
> - kiocb.ki_flags = IOCB_DIRECT;
> + if (nfsd_analyze_write_dio(rqstp, fhp, nf, offset,
> + *cnt, &write_dio))
> + dio_aligned = true;
> break;
> case NFSD_IO_DONTCACHE:
> kiocb.ki_flags = IOCB_DONTCACHE;
> @@ -1399,11 +1502,21 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
> break;
> }
>
> + nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);
> + n_iters = nfsd_setup_write_iters(&iter, rqstp->rq_bvec, nvecs, *cnt, &write_dio);
> +
> since = READ_ONCE(file->f_wb_err);
> if (verf)
> nfsd_copy_write_verifier(verf, nn);
> *cnt = 0;
> for (int i = 0; i < n_iters; i++) {
> + if (dio_aligned) {
> + if (iov_iter_is_aligned(&iter[i], nf->nf_dio_mem_align - 1,
> + nf->nf_dio_offset_align - 1))
> + kiocb.ki_flags |= IOCB_DIRECT;
> + else
> + kiocb.ki_flags &= ~IOCB_DIRECT;
> + }
> host_err = vfs_iocb_iter_write(file, &kiocb, &iter[i]);
> if (host_err < 0) {
> commit_reset_write_verifier(nn, rqstp, host_err);
--
Chuck Lever
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned
2025-08-05 14:55 ` Chuck Lever
@ 2025-08-05 19:02 ` Mike Snitzer
0 siblings, 0 replies; 9+ messages in thread
From: Mike Snitzer @ 2025-08-05 19:02 UTC (permalink / raw)
To: Chuck Lever; +Cc: Jeff Layton, linux-nfs
On Tue, Aug 05, 2025 at 10:55:06AM -0400, Chuck Lever wrote:
> On 7/31/25 7:06 PM, Mike Snitzer wrote:
> > If NFSD_IO_DIRECT is used, split any misaligned WRITE into a start,
> > middle and end as needed. The large middle extent is DIO-aligned and
> > the start and/or end are misaligned. Buffered IO is used for the
> > misaligned extents and O_DIRECT is used for the middle DIO-aligned
> > extent.
> >
> > The nfsd_analyze_write_dio trace event shows how NFSD splits a given
> > misaligned WRITE into a mix of misaligned extent(s) and a DIO-aligned
> > extent.
> >
> > This combination of trace events is useful:
> >
> > echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_opened/enable
> > echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_analyze_write_dio/enable
> > echo 1 > /sys/kernel/tracing/events/nfsd/nfsd_write_io_done/enable
> > echo 1 > /sys/kernel/tracing/events/xfs/xfs_file_direct_write/enable
> >
> > Which for this dd command:
> >
> > dd if=/dev/zero of=/mnt/share1/test bs=47008 count=2 oflag=direct
> >
> > Results in:
> >
> > nfsd-55714 [043] ..... 79976.260851: nfsd_write_opened: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008
> > nfsd-55714 [043] ..... 79976.260852: nfsd_analyze_write_dio: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008 start=0+0 middle=0+45056 end=45056+1952
> > nfsd-55714 [043] ..... 79976.260857: xfs_file_direct_write: dev 259:12 ino 0x3e00008f disize 0x0 pos 0x0 bytecount 0xb000
> > nfsd-55714 [043] ..... 79976.260965: nfsd_write_io_done: xid=0x966c5d2d fh_hash=0x4d34e6c1 offset=0 len=47008
> >
> > nfsd-55714 [043] ..... 79976.307762: nfsd_write_opened: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008
> > nfsd-55714 [043] ..... 79976.307762: nfsd_analyze_write_dio: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008 start=47008+2144 middle=49152+40960 end=90112+3904
> > nfsd-55714 [043] ..... 79976.307797: xfs_file_direct_write: dev 259:12 ino 0x3e00008f disize 0xc000 pos 0xc000 bytecount 0xa000
> > nfsd-55714 [043] ..... 79976.307866: nfsd_write_io_done: xid=0x67e5ce6f fh_hash=0x4d34e6c1 offset=47008 len=47008
> >
> > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > Reviewed-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/nfsd/vfs.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++----
> > 1 file changed, 124 insertions(+), 11 deletions(-)
>
> The diffstat tells a worrying story.
>
> For the READ path, nfsd_iter_read() is the fallback -- the hot path
> right now is splice reads. So adding instruction path length in
> nfsd_iter_read() is a concern, but it's not an immediate problem.
>
> For the write side, there is only one path, which is ballooning with
> this set of patches. This is bound to have an impact on page cache
> writes, which are still the default write I/O mode.
>
> This is why I'm hesitant to apply this series as it is currently.
>
> If I might suggest a possible action/recourse: Perhaps the patches can
> be restructured so that the default cached write mechanism retains a
> short IPL. We can leave the de-duplication and other optimizations until
> we have field results from our experiments.
The default case has an extra memset() and some extra NULL pointer
checks, but otherwise I don't see anything that is reason for concern.
Can you be more specific? Have you quantified something in practice
or this is purely from looking at the diffstat? Avoiding needless
function calls (that should/could be inlined due to only one caller)
is your concern?
Or is wanting to somehow avoid any of this misaligned DIO support
until/unless the user enabled NFSD_IO_DIRECT via debugfs? I've
(ab)used jump_labels in the past to micro-optimize away code that
should only be active if opt-in occurs. But it ends up being pretty
gross, and I'm left unsure that jump_labels are sufficiently
light-weight to be worth it.
I've just posted v4... we can continue this discussion wherever you'd
like.
Thanks,
Mike
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH v3 4/4] NFSD: handle unaligned DIO for NFS reexport
2025-07-31 23:06 [PATCH v3 0/4] NFSD DIRECT: add handling for misaligned WRITEs Mike Snitzer
` (2 preceding siblings ...)
2025-07-31 23:06 ` [PATCH v3 3/4] NFSD: issue WRITEs using O_DIRECT even if IO is misaligned Mike Snitzer
@ 2025-07-31 23:06 ` Mike Snitzer
3 siblings, 0 replies; 9+ messages in thread
From: Mike Snitzer @ 2025-07-31 23:06 UTC (permalink / raw)
To: Chuck Lever, Jeff Layton; +Cc: linux-nfs
NFS doesn't have any DIO alignment constraints but it doesn't support
STATX_DIOALIGN, so update NFSD such that it doesn't disable the use of
NFSD_IO_DIRECT if it is reexporting NFS.
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
fs/nfs/export.c | 3 ++-
fs/nfsd/filecache.c | 11 +++++++++++
include/linux/exportfs.h | 13 +++++++++++++
3 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/fs/nfs/export.c b/fs/nfs/export.c
index e9c233b6fd209..2cae75ba6b35d 100644
--- a/fs/nfs/export.c
+++ b/fs/nfs/export.c
@@ -155,5 +155,6 @@ const struct export_operations nfs_export_ops = {
EXPORT_OP_REMOTE_FS |
EXPORT_OP_NOATOMIC_ATTR |
EXPORT_OP_FLUSH_ON_CLOSE |
- EXPORT_OP_NOLOCKS,
+ EXPORT_OP_NOLOCKS |
+ EXPORT_OP_NO_DIOALIGN_NEEDED,
};
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 5601e839a72da..ea489dd44fd9a 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -1066,6 +1066,17 @@ nfsd_file_getattr(const struct svc_fh *fhp, struct nfsd_file *nf)
nfsd_io_cache_write != NFSD_IO_DIRECT))
return nfs_ok;
+ if (exportfs_handles_unaligned_dio(nf->nf_file->f_path.mnt->mnt_sb->s_export_op)) {
+ /* Underlying filesystem doesn't support STATX_DIOALIGN
+ * but it can handle all unaligned DIO, so establish
+ * DIO alignment that is accommodating.
+ */
+ nf->nf_dio_mem_align = 4;
+ nf->nf_dio_offset_align = PAGE_SIZE;
+ nf->nf_dio_read_offset_align = nf->nf_dio_offset_align;
+ return nfs_ok;
+ }
+
status = fh_getattr(fhp, &stat);
if (status != nfs_ok)
return status;
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 9369a607224c1..626b8486dd985 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -247,6 +247,7 @@ struct export_operations {
*/
#define EXPORT_OP_FLUSH_ON_CLOSE (0x20) /* fs flushes file data on close */
#define EXPORT_OP_NOLOCKS (0x40) /* no file locking support */
+#define EXPORT_OP_NO_DIOALIGN_NEEDED (0x80) /* fs can handle unaligned DIO */
unsigned long flags;
};
@@ -262,6 +263,18 @@ exportfs_cannot_lock(const struct export_operations *export_ops)
return export_ops->flags & EXPORT_OP_NOLOCKS;
}
+/**
+ * exportfs_handles_unaligned_dio() - check if export can handle unaligned DIO
+ * @export_ops: the nfs export operations to check
+ *
+ * Returns true if the export can handle unaligned DIO.
+ */
+static inline bool
+exportfs_handles_unaligned_dio(const struct export_operations *export_ops)
+{
+ return export_ops->flags & EXPORT_OP_NO_DIOALIGN_NEEDED;
+}
+
extern int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
int *max_len, struct inode *parent,
int flags);
--
2.44.0
^ permalink raw reply related [flat|nested] 9+ messages in thread