From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D047CCA483 for ; Wed, 8 Jun 2022 00:38:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1388651AbiFHAcj (ORCPT ); Tue, 7 Jun 2022 20:32:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1382451AbiFGV6s (ORCPT ); Tue, 7 Jun 2022 17:58:48 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A81DA1C93A; Tue, 7 Jun 2022 12:14:08 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 0C3E9B8237B; Tue, 7 Jun 2022 19:13:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 765F7C385A2; Tue, 7 Jun 2022 19:13:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1654629227; bh=g9VhsKXrQN/jX3DPUybyMswcmuRgsxa1Z38Jhy2E7qA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hDJAhm3g6AdUEkC3Ccpv0yVgC0yNnzPPUPvIuf+C+uhIJNcOwrQz28qz6MhbH+yPE EfSs7LKksFGkzAWu7Zgd4UG6UkjZ2KjgC6lLNNiUSxnafVTlN2C1x8wlAkKVDVv+F2 DNoN3uPRAmk4nswbf6v4hE3tGttwxd34MeMlKZjY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Waiman Long , Al Viro , David Howells , Manfred Spraul , Davidlohr Bueso , Andrew Morton , Sasha Levin Subject: [PATCH 5.18 615/879] ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() Date: Tue, 7 Jun 2022 19:02:13 +0200 Message-Id: <20220607165020.700622910@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220607165002.659942637@linuxfoundation.org> References: <20220607165002.659942637@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Waiman Long [ Upstream commit d60c4d01a98bc1942dba6e3adc02031f5519f94b ] When running the stress-ng clone benchmark with multiple testing threads, it was found that there were significant spinlock contention in sget_fc(). The contended spinlock was the sb_lock. It is under heavy contention because the following code in the critcal section of sget_fc(): hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) { if (test(old, fc)) goto share_extant_sb; } After testing with added instrumentation code, it was found that the benchmark could generate thousands of ipc namespaces with the corresponding number of entries in the mqueue's fs_supers list where the namespaces are the key for the search. This leads to excessive time in scanning the list for a match. Looking back at the mqueue calling sequence leading to sget_fc(): mq_init_ns() => mq_create_mount() => fc_mount() => vfs_get_tree() => mqueue_get_tree() => get_tree_keyed() => vfs_get_super() => sget_fc() Currently, mq_init_ns() is the only mqueue function that will indirectly call mqueue_get_tree() with a newly allocated ipc namespace as the key for searching. As a result, there will never be a match with the exising ipc namespaces stored in the mqueue's fs_supers list. So using get_tree_keyed() to do an existing ipc namespace search is just a waste of time. Instead, we could use get_tree_nodev() to eliminate the useless search. By doing so, we can greatly reduce the sb_lock hold time and avoid the spinlock contention problem in case a large number of ipc namespaces are present. Of course, if the code is modified in the future to allow mqueue_get_tree() to be called with an existing ipc namespace instead of a new one, we will have to use get_tree_keyed() in this case. The following stress-ng clone benchmark command was run on a 2-socket 48-core Intel system: ./stress-ng --clone 32 --verbose --oomable --metrics-brief -t 20 The "bogo ops/s" increased from 5948.45 before patch to 9137.06 after patch. This is an increase of 54% in performance. Link: https://lkml.kernel.org/r/20220121172315.19652-1-longman@redhat.com Fixes: 935c6912b198 ("ipc: Convert mqueue fs to fs_context") Signed-off-by: Waiman Long Cc: Al Viro Cc: David Howells Cc: Manfred Spraul Cc: Davidlohr Bueso Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- ipc/mqueue.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 7c08eb3c258d..54cb6264f8cf 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -45,6 +45,7 @@ struct mqueue_fs_context { struct ipc_namespace *ipc_ns; + bool newns; /* Set if newly created ipc namespace */ }; #define MQUEUE_MAGIC 0x19800202 @@ -427,6 +428,14 @@ static int mqueue_get_tree(struct fs_context *fc) { struct mqueue_fs_context *ctx = fc->fs_private; + /* + * With a newly created ipc namespace, we don't need to do a search + * for an ipc namespace match, but we still need to set s_fs_info. + */ + if (ctx->newns) { + fc->s_fs_info = ctx->ipc_ns; + return get_tree_nodev(fc, mqueue_fill_super); + } return get_tree_keyed(fc, mqueue_fill_super, ctx->ipc_ns); } @@ -454,6 +463,10 @@ static int mqueue_init_fs_context(struct fs_context *fc) return 0; } +/* + * mq_init_ns() is currently the only caller of mq_create_mount(). + * So the ns parameter is always a newly created ipc namespace. + */ static struct vfsmount *mq_create_mount(struct ipc_namespace *ns) { struct mqueue_fs_context *ctx; @@ -465,6 +478,7 @@ static struct vfsmount *mq_create_mount(struct ipc_namespace *ns) return ERR_CAST(fc); ctx = fc->fs_private; + ctx->newns = true; put_ipc_ns(ctx->ipc_ns); ctx->ipc_ns = get_ipc_ns(ns); put_user_ns(fc->user_ns); -- 2.35.1