From patchwork Tue Dec 22 07:47:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 11986085 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 9905EC433E0 for ; Tue, 22 Dec 2020 07:48:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56C99225AB for ; Tue, 22 Dec 2020 07:48:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726030AbgLVHst convert rfc822-to-8bit (ORCPT ); Tue, 22 Dec 2020 02:48:49 -0500 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:35155 "EHLO us-smtp-delivery-44.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725785AbgLVHst (ORCPT ); Tue, 22 Dec 2020 02:48:49 -0500 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-NnEHhwp-MdWNip3acu6hiw-1; Tue, 22 Dec 2020 02:47:49 -0500 X-MC-Unique: NnEHhwp-MdWNip3acu6hiw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 17830800D62; Tue, 22 Dec 2020 07:47:48 +0000 (UTC) Received: from mickey.themaw.net (ovpn-116-49.sin2.redhat.com [10.67.116.49]) by smtp.corp.redhat.com (Postfix) with ESMTP id 94D57299AD; Tue, 22 Dec 2020 07:47:42 +0000 (UTC) Subject: [PATCH 2/6] kernfs: use VFS negative dentry caching From: Ian Kent To: Fox Chen Cc: Tejun Heo , Greg Kroah-Hartman , Rick Lindsley , Al Viro , David Howells , Miklos Szeredi , linux-fsdevel Date: Tue, 22 Dec 2020 15:47:39 +0800 Message-ID: <160862325932.291330.15146665974057046065.stgit@mickey.themaw.net> In-Reply-To: <160862320263.291330.9467216031366035418.stgit@mickey.themaw.net> References: <160862320263.291330.9467216031366035418.stgit@mickey.themaw.net> User-Agent: StGit/0.21 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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. Signed-off-by: Ian Kent --- fs/kernfs/dir.c | 45 +++++++++++++++++++++++++++++++-------------- 1 file changed, 31 insertions(+), 14 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index c52190acda8a..34b15b95a1c2 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1032,17 +1032,37 @@ struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent, static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags) { + struct kernfs_node *parent; struct kernfs_node *kn; if (flags & LOOKUP_RCU) return -ECHILD; - /* Always perform fresh lookup for negatives */ - if (d_really_is_negative(dentry)) - goto out_bad_unlocked; + mutex_lock(&kernfs_mutex); kn = kernfs_dentry_node(dentry); - mutex_lock(&kernfs_mutex); + + /* Negative hashed dentry? */ + if (!kn) { + /* If the kernfs node can be found this is a stale negative + * hashed dentry so it must be discarded and the lookup redone. + */ + parent = kernfs_dentry_node(dentry->d_parent); + if (parent) { + const void *ns = NULL; + + if (kernfs_ns_enabled(parent)) + ns = kernfs_info(dentry->d_parent->d_sb)->ns; + kn = kernfs_find_ns(parent, dentry->d_name.name, ns); + if (kn) + goto out_bad; + } + + /* The kernfs node doesn't exist, leave the dentry negative + * and return success. + */ + goto out; + } /* The kernfs node has been deactivated */ if (!kernfs_active_read(kn)) @@ -1060,12 +1080,11 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags) if (kn->parent && kernfs_ns_enabled(kn->parent) && kernfs_info(dentry->d_sb)->ns != kn->ns) goto out_bad; - +out: mutex_unlock(&kernfs_mutex); return 1; out_bad: mutex_unlock(&kernfs_mutex); -out_bad_unlocked: return 0; } @@ -1080,7 +1099,7 @@ 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); @@ -1090,11 +1109,9 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir, kn = kernfs_find_ns(parent, dentry->d_name.name, ns); - /* no such entry */ - if (!kn || !kernfs_active(kn)) { - ret = NULL; - goto out_unlock; - } + /* no such entry, retain as negative hashed dentry */ + if (!kn || !kernfs_active(kn)) + goto out_negative; /* attach dentry and inode */ inode = kernfs_get_inode(dir->i_sb, kn); @@ -1102,10 +1119,10 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir, ret = ERR_PTR(-ENOMEM); goto out_unlock; } - +out_negative: /* instantiate and hash dentry */ ret = d_splice_alias(inode, dentry); - out_unlock: +out_unlock: mutex_unlock(&kernfs_mutex); return ret; }