From patchwork Fri Jul 16 09:28:24 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 12381813 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE7E0C636CA for ; Fri, 16 Jul 2021 09:37:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 952F6613D8 for ; Fri, 16 Jul 2021 09:37:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234249AbhGPJkf (ORCPT ); Fri, 16 Jul 2021 05:40:35 -0400 Received: from icp-osb-irony-out9.external.iinet.net.au ([203.59.1.226]:22594 "EHLO icp-osb-irony-out9.external.iinet.net.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233986AbhGPJkd (ORCPT ); Fri, 16 Jul 2021 05:40:33 -0400 X-Greylist: delayed 556 seconds by postgrey-1.27 at vger.kernel.org; Fri, 16 Jul 2021 05:40:26 EDT X-SMTP-MATCH: 0 IronPort-HdrOrdr: A9a23:HCUZiq2XJJWX1INLK/FgJQqjBIgkLtp133Aq2lEZdPU1SKClfqWV98jzuiWatN98Yh8dcLK7WJVoMEm8yXcd2+B4V9qftW/dyQmVxepZnOjfKlPbakrD398Y+aB8c7VvTP3cZGIK6/oSOTPIdurIFuP3lJyVuQ== X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2AbBwA6UPFg/y2ELHlQCh4BAQsSDEAJgUULAoN2bIQCRpATAQEBAQEBBoFAimmFb1+KKYF8CwEBAQEBAQEBAUoEAQGEVAKCfAElNAkOAgQVAQEBBQEBAQEBBgMBgQ6FdUMBDAGFdQYjBFIQGA0CGA4CAkcQBgEShVMlp2d/MxoCZYpDgRAqAYcIgmiDeiccfYEQgRUzA4EFgiiEF4NEgmQEglJFAYEOFIFkSJIRgnsBRohtgSxbnQyDLp5kF5VPA5B1hwePAacOghRNLgqDJFAZjjgBFo46Ny84AgYKAQEDCYJyhyItghgBAQ X-IPAS-Result: A2AbBwA6UPFg/y2ELHlQCh4BAQsSDEAJgUULAoN2bIQCRpATAQEBAQEBBoFAimmFb1+KKYF8CwEBAQEBAQEBAUoEAQGEVAKCfAElNAkOAgQVAQEBBQEBAQEBBgMBgQ6FdUMBDAGFdQYjBFIQGA0CGA4CAkcQBgEShVMlp2d/MxoCZYpDgRAqAYcIgmiDeiccfYEQgRUzA4EFgiiEF4NEgmQEglJFAYEOFIFkSJIRgnsBRohtgSxbnQyDLp5kF5VPA5B1hwePAacOghRNLgqDJFAZjjgBFo46Ny84AgYKAQEDCYJyhyItghgBAQ X-IronPort-AV: E=Sophos;i="5.84,244,1620662400"; d="scan'208";a="329873575" Received: from unknown (HELO web.messagingengine.com) ([121.44.132.45]) by icp-osb-irony-out9.iinet.net.au with ESMTP; 16 Jul 2021 17:28:24 +0800 Subject: [PATCH v8 2/5] kernfs: use VFS negative dentry caching From: Ian Kent To: Greg Kroah-Hartman , Tejun Heo Cc: Eric Sandeen , Fox Chen , Brice Goglin , Al Viro , Rick Lindsley , David Howells , Miklos Szeredi , Marcelo Tosatti , "Eric W. Biederman" , Carlos Maiolino , linux-fsdevel , Kernel Mailing List Date: Fri, 16 Jul 2021 17:28:24 +0800 Message-ID: <162642770420.63632.15791924970508867106.stgit@web.messagingengine.com> In-Reply-To: <162642752894.63632.5596341704463755308.stgit@web.messagingengine.com> References: <162642752894.63632.5596341704463755308.stgit@web.messagingengine.com> User-Agent: StGit/0.23 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org If there are many lookups for non-existent paths these negative lookups can lead to a lot of overhead during path walks. The VFS allows dentries to be created as negative and hashed, and caches them so they can be used to reduce the fairly high overhead alloc/free cycle that occurs during these lookups. Use the kernfs node parent revision to identify if a change has been made to the containing directory so that the negative dentry can be discarded and the lookup redone. Signed-off-by: Ian Kent Reviewed-by: Miklos Szeredi --- fs/kernfs/dir.c | 55 +++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 35 insertions(+), 20 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index b3d1bc0f317d..0b21a8f961ac 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1039,9 +1039,31 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags) if (flags & LOOKUP_RCU) return -ECHILD; - /* Always perform fresh lookup for negatives */ - if (d_really_is_negative(dentry)) - goto out_bad_unlocked; + /* Negative hashed dentry? */ + if (d_really_is_negative(dentry)) { + struct kernfs_node *parent; + + /* If the kernfs parent node has changed discard and + * proceed to ->lookup. + */ + mutex_lock(&kernfs_mutex); + spin_lock(&dentry->d_lock); + parent = kernfs_dentry_node(dentry->d_parent); + if (parent) { + if (kernfs_dir_changed(parent, dentry)) { + spin_unlock(&dentry->d_lock); + mutex_unlock(&kernfs_mutex); + return 0; + } + } + spin_unlock(&dentry->d_lock); + mutex_unlock(&kernfs_mutex); + + /* The kernfs parent node hasn't changed, leave the + * dentry negative and return success. + */ + return 1; + } kn = kernfs_dentry_node(dentry); mutex_lock(&kernfs_mutex); @@ -1067,7 +1089,6 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags) return 1; out_bad: mutex_unlock(&kernfs_mutex); -out_bad_unlocked: return 0; } @@ -1082,33 +1103,27 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir, struct dentry *ret; struct kernfs_node *parent = dir->i_private; struct kernfs_node *kn; - struct inode *inode; + struct inode *inode = NULL; const void *ns = NULL; mutex_lock(&kernfs_mutex); - if (kernfs_ns_enabled(parent)) ns = kernfs_info(dir->i_sb)->ns; kn = kernfs_find_ns(parent, dentry->d_name.name, ns); - - /* no such entry */ - if (!kn || !kernfs_active(kn)) { - ret = NULL; - goto out_unlock; - } - /* attach dentry and inode */ - inode = kernfs_get_inode(dir->i_sb, kn); - if (!inode) { - ret = ERR_PTR(-ENOMEM); - goto out_unlock; + if (kn && kernfs_active(kn)) { + inode = kernfs_get_inode(dir->i_sb, kn); + if (!inode) + inode = ERR_PTR(-ENOMEM); } - - /* instantiate and hash dentry */ + /* Needed only for negative dentry validation */ + if (!inode) + kernfs_set_rev(parent, dentry); + /* instantiate and hash (possibly negative) dentry */ ret = d_splice_alias(inode, dentry); - out_unlock: mutex_unlock(&kernfs_mutex); + return ret; }