Re: Client never uses DATA_SYNC

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Nov 05, 2014 at 12:53:17AM -0800, Christoph Hellwig wrote:
> 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.

Makes sense to me.--b.

> 

> >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
>