Re: Client never uses DATA_SYNC

[Christoph Hellwig <hch@infradead.org>]

[-- Attachment #1: Type: text/plain, Size: 1325 bytes --]

On Tue, Nov 04, 2014 at 03:38:28PM -0500, Trond Myklebust wrote:
> Hi Ben,
> 
> On Tue, Nov 4, 2014 at 10:47 AM, Benjamin Coddington
> <bcodding@redhat.com> wrote:
> > I have a customer that would like the client to use DATA_SYNC instead of
> > FILE_SYNC when writing a file with O_DSYNC.  It looks like the client will
> > only use FILE_SYNC since:
> >
> > 87ed5eb44ad9338b1617 NFS: Don't use DATA_SYNC writes
> > http://marc.info/?l=git-commits-head&m=131180398113265&w=2
> >
> > I've been unable to dig up any other discussion on this, so I think it
> > has just been an overlooked point until now.  I'm only starting to
> > figure out what would need to change for this, and I thought that while
> > I do that I'd ask the list if anyone thinks that serious implementation
> > issues might emerge if this were attempted.
> 
> I'm not aware of any servers that make a real distinction between
> FILE_SYNC and DATA_SYNC. Has anybody done any performance measurements
> to show that it is worth the effort?

For a fully allocated file the difference between fdatasync and fsync
or O_DSYNC / O_SYNC can make a difference, this is especially notiable
on data base workloads that do lots of small I/O on fully preallocated
files.

Implementing this difference for the Linux NFS server also seem fairly
trivial, patch attached.


[-- Attachment #2: 0001-nfsd-implement-DATA_SYNC4-support.patch --]
[-- Type: text/plain, Size: 5562 bytes --]

>From 61fee1aacf2f31b6fb1bb90d90f5e625994970f6 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Wed, 5 Nov 2014 09:50:35 +0100
Subject: nfsd: implement DATA_SYNC4 support

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/nfsd/nfs3proc.c |  4 ++--
 fs/nfsd/nfs4proc.c |  7 +++----
 fs/nfsd/nfsproc.c  |  7 ++-----
 fs/nfsd/vfs.c      | 14 +++++++-------
 fs/nfsd/vfs.h      |  3 ++-
 5 files changed, 16 insertions(+), 19 deletions(-)

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 12f2aab..cc9622f 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -191,12 +191,12 @@ nfsd3_proc_write(struct svc_rqst *rqstp, struct nfsd3_writeargs *argp,
 				argp->stable? " stable" : "");
 
 	fh_copy(&resp->fh, &argp->fh);
-	resp->committed = argp->stable;
 	nfserr = nfsd_write(rqstp, &resp->fh, NULL,
 				   argp->offset,
 				   rqstp->rq_vec, argp->vlen,
 				   &cnt,
-				   &resp->committed);
+				   argp->stable);
+	resp->committed = argp->stable;
 	resp->count = cnt;
 	RETURN_STATUS(nfserr);
 }
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index c4a2adc..b11fd3b 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -998,15 +998,14 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	}
 
 	cnt = write->wr_buflen;
-	write->wr_how_written = write->wr_stable_how;
 	gen_boot_verifier(&write->wr_verifier, SVC_NET(rqstp));
 
 	nvecs = fill_in_write_vector(rqstp->rq_vec, write);
 	WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec));
 
-	status =  nfsd_write(rqstp, &cstate->current_fh, filp,
-			     write->wr_offset, rqstp->rq_vec, nvecs,
-			     &cnt, &write->wr_how_written);
+	status = nfsd_write(rqstp, &cstate->current_fh, filp, write->wr_offset,
+			    rqstp->rq_vec, nvecs, &cnt, write->wr_stable_how);
+	write->wr_how_written = write->wr_stable_how;
 	if (filp)
 		fput(filp);
 
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index b868073..90caa00 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -158,7 +158,6 @@ nfsd_proc_write(struct svc_rqst *rqstp, struct nfsd_writeargs *argp,
 					struct nfsd_attrstat  *resp)
 {
 	__be32	nfserr;
-	int	stable = 1;
 	unsigned long cnt = argp->len;
 
 	dprintk("nfsd: WRITE    %s %d bytes at %d\n",
@@ -166,10 +165,8 @@ nfsd_proc_write(struct svc_rqst *rqstp, struct nfsd_writeargs *argp,
 		argp->len, argp->offset);
 
 	nfserr = nfsd_write(rqstp, fh_copy(&resp->fh, &argp->fh), NULL,
-				   argp->offset,
-				   rqstp->rq_vec, argp->vlen,
-			           &cnt,
-				   &stable);
+			    argp->offset, rqstp->rq_vec, argp->vlen,
+			    &cnt, NFS_FILE_SYNC);
 	return nfsd_return_attrs(nfserr, resp);
 }
 
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 989129e..2ea8ff6 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -927,7 +927,7 @@ static int wait_for_concurrent_writes(struct file *file)
 static __be32
 nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 				loff_t offset, struct kvec *vec, int vlen,
-				unsigned long *cnt, int *stablep)
+				unsigned long *cnt, enum nfs3_stable_how stable)
 {
 	struct svc_export	*exp;
 	struct dentry		*dentry;
@@ -935,7 +935,6 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 	mm_segment_t		oldfs;
 	__be32			err = 0;
 	int			host_err;
-	int			stable = *stablep;
 	int			use_wgather;
 	loff_t			pos = offset;
 	unsigned int		pflags = current->flags;
@@ -956,7 +955,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 	use_wgather = (rqstp->rq_vers == 2) && EX_WGATHER(exp);
 
 	if (!EX_ISSYNC(exp))
-		stable = 0;
+		stable = NFS_UNSTABLE;
 
 	/* Write the data. */
 	oldfs = get_fs(); set_fs(KERNEL_DS);
@@ -972,7 +971,8 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 		if (use_wgather)
 			host_err = wait_for_concurrent_writes(file);
 		else
-			host_err = vfs_fsync_range(file, offset, offset+*cnt, 0);
+			host_err = vfs_fsync_range(file, offset, offset+*cnt,
+						   stable == NFS_DATA_SYNC);
 	}
 
 out_nfserr:
@@ -1051,7 +1051,7 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 __be32
 nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 		loff_t offset, struct kvec *vec, int vlen, unsigned long *cnt,
-		int *stablep)
+		enum nfs3_stable_how stable)
 {
 	__be32			err = 0;
 
@@ -1061,7 +1061,7 @@ nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 		if (err)
 			goto out;
 		err = nfsd_vfs_write(rqstp, fhp, file, offset, vec, vlen, cnt,
-				stablep);
+				stable);
 	} else {
 		err = nfsd_open(rqstp, fhp, S_IFREG, NFSD_MAY_WRITE, &file);
 		if (err)
@@ -1069,7 +1069,7 @@ nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 
 		if (cnt)
 			err = nfsd_vfs_write(rqstp, fhp, file, offset, vec, vlen,
-					     cnt, stablep);
+					     cnt, stable);
 		nfsd_close(file);
 	}
 out:
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index c2ff3f1..3cb8e55 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -81,7 +81,8 @@ __be32		nfsd_readv(struct file *, loff_t, struct kvec *, int,
 __be32 		nfsd_read(struct svc_rqst *, struct svc_fh *,
 				loff_t, struct kvec *, int, unsigned long *);
 __be32 		nfsd_write(struct svc_rqst *, struct svc_fh *,struct file *,
-				loff_t, struct kvec *,int, unsigned long *, int *);
+				loff_t, struct kvec *,int, unsigned long *,
+				enum nfs3_stable_how);
 __be32		nfsd_readlink(struct svc_rqst *, struct svc_fh *,
 				char *, int *);
 __be32		nfsd_symlink(struct svc_rqst *, struct svc_fh *,
-- 
1.9.1