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

[Jeff Layton <jlayton@kernel.org>]

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?


>  		}
>  	} else
>  		status = nfserr_jukebox;
> diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
> index 24ddf60e8434..e3d6ca2b6030 100644
> --- a/fs/nfsd/filecache.h
> +++ b/fs/nfsd/filecache.h
> @@ -54,6 +54,10 @@ struct nfsd_file {
>  	struct list_head	nf_gc;
>  	struct rcu_head		nf_rcu;
>  	ktime_t			nf_birthtime;
> +
> +	u32			nf_dio_mem_align;
> +	u32			nf_dio_offset_align;
> +	u32			nf_dio_read_offset_align;
>  };
>  
>  int nfsd_file_cache_init(void);
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index f4a3cc9e31e0..bdba2ba828a6 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -677,8 +677,12 @@ __be32 fh_getattr(const struct svc_fh *fhp, struct kstat *stat)
>  		.mnt		= fhp->fh_export->ex_path.mnt,
>  		.dentry		= fhp->fh_dentry,
>  	};
> +	struct inode *inode = d_inode(p.dentry);
>  	u32 request_mask = STATX_BASIC_STATS;
>  
> +	if (S_ISREG(inode->i_mode))
> +		request_mask |= (STATX_DIOALIGN | STATX_DIO_READ_ALIGN);
> +
>  	if (fhp->fh_maxsize == NFS4_FHSIZE)
>  		request_mask |= (STATX_BTIME | STATX_CHANGE_COOKIE);
>  

-- 
Jeff Layton <jlayton@kernel.org>