nfsd: Set PF_LOCAL_THROTTLE on local filesystems only

Don't set PF_LOCAL_THROTTLE on remote filesystems like NFS, since they
aren't expected to ever be subject to double buffering.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfs/export.c

@@ -171,5 +171,6 @@ const struct export_operations nfs_export_ops = {
 	.encode_fh = nfs_encode_fh,
 	.fh_to_dentry = nfs_fh_to_dentry,
 	.get_parent = nfs_get_parent,
-	.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|EXPORT_OP_CLOSE_BEFORE_UNLINK,
+	.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|
+		EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS,
 };

fs/nfsd/vfs.c

@@ -978,18 +978,25 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 				__be32 *verf)
 {
 	struct file		*file = nf->nf_file;
+	struct super_block	*sb = file_inode(file)->i_sb;
 	struct svc_export	*exp;
 	struct iov_iter		iter;
 	__be32			nfserr;
 	int			host_err;
 	int			use_wgather;
 	loff_t			pos = offset;
+	unsigned long		exp_op_flags = 0;
 	unsigned int		pflags = current->flags;
 	rwf_t			flags = 0;
+	bool			restore_flags = false;
 
 	trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
 
-	if (test_bit(RQ_LOCAL, &rqstp->rq_flags))
+	if (sb->s_export_op)
+		exp_op_flags = sb->s_export_op->flags;
+
+	if (test_bit(RQ_LOCAL, &rqstp->rq_flags) &&
+	    !(exp_op_flags & EXPORT_OP_REMOTE_FS)) {
 		/*
 		 * We want throttling in balance_dirty_pages()
 		 * and shrink_inactive_list() to only consider
@@ -998,6 +1005,8 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 		 * the client's dirty pages or its congested queue.
 		 */
 		current->flags |= PF_LOCAL_THROTTLE;
+		restore_flags = true;
+	}
 
 	exp = fhp->fh_export;
 	use_wgather = (rqstp->rq_vers == 2) && EX_WGATHER(exp);
@@ -1049,7 +1058,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 		trace_nfsd_write_err(rqstp, fhp, offset, host_err);
 		nfserr = nfserrno(host_err);
 	}
-	if (test_bit(RQ_LOCAL, &rqstp->rq_flags))
+	if (restore_flags)
 		current_restore_flags(pflags, PF_LOCAL_THROTTLE);
 	return nfserr;
 }

include/linux/exportfs.h

@@ -216,6 +216,7 @@ struct export_operations {
 #define	EXPORT_OP_NOWCC			(0x1) /* don't collect v3 wcc data */
 #define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */
 #define	EXPORT_OP_CLOSE_BEFORE_UNLINK	(0x4) /* close files before unlink */
+#define EXPORT_OP_REMOTE_FS		(0x8) /* Filesystem is remote */
 	unsigned long	flags;
 };