From patchwork Fri Jul 16 09:28:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ian Kent X-Patchwork-Id: 12381811 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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 808ECC12002 for ; Fri, 16 Jul 2021 09:37:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64DAF613F2 for ; Fri, 16 Jul 2021 09:37:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234095AbhGPJkc (ORCPT ); Fri, 16 Jul 2021 05:40:32 -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 S229833AbhGPJkb (ORCPT ); Fri, 16 Jul 2021 05:40:31 -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:SxB18qHuKXxEEb4ipLqE0seALOsnbusQ8zAXPiFKJSC9F/byqynAppsmPHPP5gr5OktBpTnwAsi9qBrnnPYejLX5W43SPjUO01HYT72Kg7GSpAHIKmnT8fNcyLclU4UWMqyXMbGit7ee3OBvKadF/OW6 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2AQBwA6UPFg/y2ELHlQCoEJCYFQAoF0ggKEbkaQEwEBAQEBAQaBQIpphW+LCIF8CwEBAQEBAQEBAUoEAQGEVIJ+ASU0CQ4CBBUBAQEFAQEBAQEGAwGBDoV1QwEMAYYeVigNAhgOAkkWAYVlJadngTIaAmWKQ4EQKgGHCIJohCEcfYEQgUgDgjh1hBeDRIJkBIJ4GQYBAXMaARM4NCARKhYPERgWNzCRBSaCewFGihlbnQyDLp5kF4NMkgMDFpBflgiCHJ1ihxCCFE0uCoMlTxmdCTdnAgYKAQEDCYJyhyInBoIYAQE X-IPAS-Result: A2AQBwA6UPFg/y2ELHlQCoEJCYFQAoF0ggKEbkaQEwEBAQEBAQaBQIpphW+LCIF8CwEBAQEBAQEBAUoEAQGEVIJ+ASU0CQ4CBBUBAQEFAQEBAQEGAwGBDoV1QwEMAYYeVigNAhgOAkkWAYVlJadngTIaAmWKQ4EQKgGHCIJohCEcfYEQgUgDgjh1hBeDRIJkBIJ4GQYBAXMaARM4NCARKhYPERgWNzCRBSaCewFGihlbnQyDLp5kF4NMkgMDFpBflgiCHJ1ihxCCFE0uCoMlTxmdCTdnAgYKAQEDCYJyhyInBoIYAQE X-IronPort-AV: E=Sophos;i="5.84,244,1620662400"; d="scan'208";a="329873529" Received: from unknown (HELO web.messagingengine.com) ([121.44.132.45]) by icp-osb-irony-out9.iinet.net.au with ESMTP; 16 Jul 2021 17:28:13 +0800 Subject: [PATCH v8 0/5] kernfs: proposed locking and concurrency improvement 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 17:28:13 +0800 Message-ID: <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 There have been a few instances of contention on the kernfs_mutex during path walks, a case on very large IBM systems seen by myself, a report by Brice Goglin and followed up by Fox Chen, and I've since seen a couple of other reports by CoreOS users. The common thread is a large number of kernfs path walks leading to slowness of path walks due to kernfs_mutex contention. The problem being that changes to the VFS over some time have increased it's concurrency capabilities to an extent that kernfs's use of a mutex is no longer appropriate. There's also an issue of walks for non-existent paths causing contention if there are quite a few of them which is a less common problem. This patch series is relatively straight forward. All it does is add the ability to take advantage of VFS negative dentry caching to avoid needless dentry alloc/free cycles for lookups of paths that don't exit and change the kernfs_mutex to a read/write semaphore. The patch that tried to stay in VFS rcu-walk mode during path walks has been dropped for two reasons. First, it doesn't actually give very much improvement and, second, if there's a place where mistakes could go unnoticed it would be in that path. This makes the patch series simpler to review and reduces the likelihood of problems going unnoticed and popping up later. Changes since v7: - remove extra tab in helper kernfs_dir_changed. - fix thinko adding an unnecessary kernfs_inc_rev() in kernfs_rename_ns(). Changes since v6: - ensure negative dentry as rename target gets invalidated. - don't bother checking if node is a directory in revision helpers. - don't use dget_parent(), just use dentry d_lock to ensure parent is stable. - fix kernfs_iop_getattr() and kernfs_iop_permission() locking. - drop add kernfs_need_inode_refresh() patch, it can't be used. Changes since v5: - change kernfs_dir_changed() comparison. - move negative dentry out from under kernfs node lock in revalidate. - only set d_time for negative dentries. - add patch to move d_splice_alias() out from under kernfs node lock in lookup. Changes since v4: - fixed kernfs_active() naming. - added back kernfs_node revision patch to use for negative dentry validation. - minor updates to patch descriptions. Changes since v3: - remove unneeded indirection when referencing the super block. - check if inode attribute update is actually needed. Changes since v2: - actually fix the inode attribute update locking. - drop the patch that tried to stay in rcu-walk mode. - drop the use a revision to identify if a directory has changed patch. Changes since v1: - fix locking in .permission() and .gated() by re-factoring the attribute handling code. --- Ian Kent (5): kernfs: add a revision to identify directory node changes kernfs: use VFS negative dentry caching kernfs: switch kernfs to use an rwsem kernfs: use i_lock to protect concurrent inode updates kernfs: dont call d_splice_alias() under kernfs node lock fs/kernfs/dir.c | 151 ++++++++++++++++++++---------------- fs/kernfs/file.c | 4 +- fs/kernfs/inode.c | 26 ++++--- fs/kernfs/kernfs-internal.h | 5 +- fs/kernfs/mount.c | 12 +-- fs/kernfs/symlink.c | 4 +- include/linux/kernfs.h | 2 +- 7 files changed, 112 insertions(+), 92 deletions(-) -- Ian