From patchwork Tue Jun 15 10:26:21 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 12321055 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 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 8CE7EC48BE5 for ; Tue, 15 Jun 2021 10:26:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7319661443 for ; Tue, 15 Jun 2021 10:26:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231656AbhFOK2r convert rfc822-to-8bit (ORCPT ); Tue, 15 Jun 2021 06:28:47 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:36891 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231644AbhFOK2l (ORCPT ); Tue, 15 Jun 2021 06:28:41 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-354--Mj98SNwNciMrXmnXG443A-1; Tue, 15 Jun 2021 06:26:31 -0400 X-MC-Unique: -Mj98SNwNciMrXmnXG443A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8E06F1084F47; Tue, 15 Jun 2021 10:26:29 +0000 (UTC) Received: from web.messagingengine.com (ovpn-116-40.sin2.redhat.com [10.67.116.40]) by smtp.corp.redhat.com (Postfix) with ESMTP id C70DF60E3A; Tue, 15 Jun 2021 10:26:22 +0000 (UTC) Subject: [PATCH v7 3/6] 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: Tue, 15 Jun 2021 18:26:21 +0800 Message-ID: <162375278118.232295.14989882873957232796.stgit@web.messagingengine.com> In-Reply-To: <162375263398.232295.14755578426619198534.stgit@web.messagingengine.com> References: <162375263398.232295.14755578426619198534.stgit@web.messagingengine.com> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=raven@themaw.net X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: themaw.net 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 | 52 ++++++++++++++++++++++++++++++++-------------------- 1 file changed, 32 insertions(+), 20 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 48704c5b6a072..f9352c9e90581 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1039,9 +1039,28 @@ 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. + */ + 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); + return 0; + } + } + spin_unlock(&dentry->d_lock); + + /* 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 +1086,6 @@ 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 +1100,27 @@ 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; }