NFS: Don't ask for readdirplus unless it can help nfs_getattr()

If attribute caching is turned off, then use of readdirplus is not going
to help stat() performance.
Readdirplus also doesn't help if a file is being written to, since we
will have to flush those writes in order to sync the mtime/ctime.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/inode.c

@@ -780,26 +780,32 @@ void nfs_setattr_update_inode(struct inode *inode, struct iattr *attr,
 }
 EXPORT_SYMBOL_GPL(nfs_setattr_update_inode);
 
-static void nfs_readdirplus_parent_cache_miss(struct dentry *dentry)
+/*
+ * Don't request help from readdirplus if the file is being written to,
+ * or if attribute caching is turned off
+ */
+static bool nfs_getattr_readdirplus_enable(const struct inode *inode)
 {
-	struct dentry *parent;
+	return nfs_server_capable(inode, NFS_CAP_READDIRPLUS) &&
+	       !nfs_have_writebacks(inode) && NFS_MAXATTRTIMEO(inode) > 5 * HZ;
+}
 
-	if (!nfs_server_capable(d_inode(dentry), NFS_CAP_READDIRPLUS))
-		return;
-	parent = dget_parent(dentry);
-	nfs_readdir_record_entry_cache_miss(d_inode(parent));
-	dput(parent);
+static void nfs_readdirplus_parent_cache_miss(struct dentry *dentry)
+{
+	if (!IS_ROOT(dentry)) {
+		struct dentry *parent = dget_parent(dentry);
+		nfs_readdir_record_entry_cache_miss(d_inode(parent));
+		dput(parent);
+	}
 }
 
 static void nfs_readdirplus_parent_cache_hit(struct dentry *dentry)
 {
-	struct dentry *parent;
-
-	if (!nfs_server_capable(d_inode(dentry), NFS_CAP_READDIRPLUS))
-		return;
-	parent = dget_parent(dentry);
-	nfs_readdir_record_entry_cache_hit(d_inode(parent));
-	dput(parent);
+	if (!IS_ROOT(dentry)) {
+		struct dentry *parent = dget_parent(dentry);
+		nfs_readdir_record_entry_cache_hit(d_inode(parent));
+		dput(parent);
+	}
 }
 
 static u32 nfs_get_valid_attrmask(struct inode *inode)
@@ -835,6 +841,7 @@ int nfs_getattr(struct user_namespace *mnt_userns, const struct path *path,
 	int err = 0;
 	bool force_sync = query_flags & AT_STATX_FORCE_SYNC;
 	bool do_update = false;
+	bool readdirplus_enabled = nfs_getattr_readdirplus_enable(inode);
 
 	trace_nfs_getattr_enter(inode);
 
@@ -843,7 +850,8 @@ int nfs_getattr(struct user_namespace *mnt_userns, const struct path *path,
 			STATX_INO | STATX_SIZE | STATX_BLOCKS;
 
 	if ((query_flags & AT_STATX_DONT_SYNC) && !force_sync) {
-		nfs_readdirplus_parent_cache_hit(path->dentry);
+		if (readdirplus_enabled)
+			nfs_readdirplus_parent_cache_hit(path->dentry);
 		goto out_no_revalidate;
 	}
 
@@ -893,15 +901,12 @@ int nfs_getattr(struct user_namespace *mnt_userns, const struct path *path,
 		do_update |= cache_validity & NFS_INO_INVALID_BLOCKS;
 
 	if (do_update) {
-		/* Update the attribute cache */
-		if (!(server->flags & NFS_MOUNT_NOAC))
+		if (readdirplus_enabled)
 			nfs_readdirplus_parent_cache_miss(path->dentry);
-		else
-			nfs_readdirplus_parent_cache_hit(path->dentry);
 		err = __nfs_revalidate_inode(server, inode);
 		if (err)
 			goto out;
-	} else
+	} else if (readdirplus_enabled)
 		nfs_readdirplus_parent_cache_hit(path->dentry);
 out_no_revalidate:
 	/* Only return attributes that were revalidated. */