Re: [PATCH v4 1/5] NFSD: filecache: add STATX_DIOALIGN and STATX_DIO_READ_ALIGN support

[Mike Snitzer <snitzer@kernel.org>]

On Wed, Jul 23, 2025 at 02:58:19PM -0400, Jeff Layton wrote:
> On Wed, 2025-07-23 at 11:43 -0400, Mike Snitzer wrote:
> > Use STATX_DIOALIGN and STATX_DIO_READ_ALIGN to get and store DIO
> > alignment attributes from underlying filesystem in associated
> > nfsd_file.  This is done when the nfsd_file is first opened for
> > a regular file.
> > 
> > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > ---
> >  fs/nfsd/filecache.c | 32 ++++++++++++++++++++++++++++++++
> >  fs/nfsd/filecache.h |  4 ++++
> >  fs/nfsd/nfsfh.c     |  4 ++++
> >  3 files changed, 40 insertions(+)
> > 
> > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> > index 8581c131338b..5447dba6c5da 100644
> > --- a/fs/nfsd/filecache.c
> > +++ b/fs/nfsd/filecache.c
> > @@ -231,6 +231,9 @@ nfsd_file_alloc(struct net *net, struct inode *inode, unsigned char need,
> >  	refcount_set(&nf->nf_ref, 1);
> >  	nf->nf_may = need;
> >  	nf->nf_mark = NULL;
> > +	nf->nf_dio_mem_align = 0;
> > +	nf->nf_dio_offset_align = 0;
> > +	nf->nf_dio_read_offset_align = 0;
> >  	return nf;
> >  }
> >  
> > @@ -1048,6 +1051,33 @@ nfsd_file_is_cached(struct inode *inode)
> >  	return ret;
> >  }
> >  
> > +static __be32
> > +nfsd_file_getattr(const struct svc_fh *fhp, struct nfsd_file *nf)
> > +{
> > +	struct inode *inode = file_inode(nf->nf_file);
> > +	struct kstat stat;
> > +	__be32 status;
> > +
> > +	/* Currently only need to get DIO alignment info for regular files */
> > +	if (!S_ISREG(inode->i_mode))
> > +		return nfs_ok;
> > +
> > +	status = fh_getattr(fhp, &stat);
> > +	if (status != nfs_ok)
> > +		return status;
> > +
> > +	if (stat.result_mask & STATX_DIOALIGN) {
> > +		nf->nf_dio_mem_align = stat.dio_mem_align;
> > +		nf->nf_dio_offset_align = stat.dio_offset_align;
> > +	}
> > +	if (stat.result_mask & STATX_DIO_READ_ALIGN)
> > +		nf->nf_dio_read_offset_align = stat.dio_read_offset_align;
> > +	else
> > +		nf->nf_dio_read_offset_align = nf->nf_dio_offset_align;
> > +
> > +	return status;
> > +}
> > +
> >  static __be32
> >  nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net,
> >  		     struct svc_cred *cred,
> > @@ -1166,6 +1196,8 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net,
> >  			}
> >  			status = nfserrno(ret);
> >  			trace_nfsd_file_open(nf, status);
> > +			if (status == nfs_ok)
> > +				status = nfsd_file_getattr(fhp, nf);
> 
> 
> Doing a getattr alongside every open could be expensive in some
> configurations (like reexported NFS). We may want to skip doing this
> getattr this if O_DIRECT isn't is use. Is that possible?

Good point, yes, should be easy enough.  Will depend on the debugfs
knobs, so will tack a patch on at the end.

Thanks,
Mike