From patchwork Mon Jul 21 03:28:28 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 4592861 Return-Path: X-Original-To: patchwork-linux-nfs@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 546729F375 for ; Mon, 21 Jul 2014 03:28:41 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 87C272010E for ; Mon, 21 Jul 2014 03:28:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BA49B2010B for ; Mon, 21 Jul 2014 03:28:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752157AbaGUD2i (ORCPT ); Sun, 20 Jul 2014 23:28:38 -0400 Received: from cantor2.suse.de ([195.135.220.15]:41059 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752007AbaGUD2i (ORCPT ); Sun, 20 Jul 2014 23:28:38 -0400 Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 31F8AAB13; Mon, 21 Jul 2014 03:28:36 +0000 (UTC) Date: Mon, 21 Jul 2014 13:28:28 +1000 From: NeilBrown To: Trond Myklebust Cc: NFS Subject: [PATCH] NFS: nfs4_do_open should add negative results to the dcache. Message-ID: <20140721132828.77f1297e@notabene.brown> X-Mailer: Claws Mail 3.10.1-123-gae895c (GTK+ 2.24.22; x86_64-suse-linux-gnu) MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, T_TVD_MIME_EPI, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP If you have an NFSv4 mounted directory which does not container 'foo' and: ls -l foo ssh $server touch foo cat foo then the 'cat' will fail (usually, depending a bit on the various cache ages). This is correct as negative looks are cached by default. However with the same initial conditions: cat foo ssh $server touch foo cat foo will usually succeed. This is because an "open" does not add a negative dentry to the dcache, while a "lookup" does. This can have negative performance effects. When "gcc" searches for an include file, it will try to "open" the file in every director in the search path. Without caching of negative "open" results, this generates much more traffic to the server than it should (or than NFSv3 does). The root of the problem is that _nfs4_open_and_get_state() will call d_add_unique() on a positive result, but not on a negative result. Compare with nfs_lookup() which calls d_materialise_unique on both a positive result and on ENOENT. This patch adds a call d_add() in the ENOENT case for _nfs4_open_and_get_state() and also calls nfs_set_verifier(). With it, many fewer "open" requests for known-non-existent files are sent to the server. Signed-off-by: NeilBrown diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c index 4bf3d97cc5a0..21fa7bddd3cb 100644 --- a/fs/nfs/nfs4proc.c +++ b/fs/nfs/nfs4proc.c @@ -2216,8 +2216,15 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata, seq = raw_seqcount_begin(&sp->so_reclaim_seqcount); ret = _nfs4_proc_open(opendata); - if (ret != 0) + if (ret != 0) { + if (ret == -ENOENT) { + d_drop(opendata->dentry); + d_add(opendata->dentry, NULL); + nfs_set_verifier(opendata->dentry, + nfs_save_change_attribute(opendata->dir->d_inode)); + } goto out; + } state = nfs4_opendata_to_nfs4_state(opendata); ret = PTR_ERR(state);