From patchwork Fri Jun 21 12:58:16 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Layton X-Patchwork-Id: 2762771 Return-Path: X-Original-To: patchwork-cifs-client@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 61DB99F756 for ; Fri, 21 Jun 2013 13:04:25 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 40F2820251 for ; Fri, 21 Jun 2013 13:04:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1CD7620253 for ; Fri, 21 Jun 2013 13:04:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161032Ab3FUNDk (ORCPT ); Fri, 21 Jun 2013 09:03:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24256 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965899Ab3FUM65 (ORCPT ); Fri, 21 Jun 2013 08:58:57 -0400 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r5LCwXWP002951 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 21 Jun 2013 08:58:33 -0400 Received: from sikun.lab.eng.rdu2.redhat.com (sikun.lab.eng.rdu2.redhat.com [10.8.0.43]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id r5LCwMii014591; Fri, 21 Jun 2013 08:58:31 -0400 From: Jeff Layton To: viro@zeniv.linux.org.uk, matthew@wil.cx, bfields@fieldses.org Cc: dhowells@redhat.com, sage@inktank.com, smfrench@gmail.com, swhiteho@redhat.com, Trond.Myklebust@netapp.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, piastryyy@gmail.com Subject: [PATCH v4 08/14] locks: avoid taking global lock if possible when waking up blocked waiters Date: Fri, 21 Jun 2013 08:58:16 -0400 Message-Id: <1371819502-26363-9-git-send-email-jlayton@redhat.com> In-Reply-To: <1371819502-26363-1-git-send-email-jlayton@redhat.com> References: <1371819502-26363-1-git-send-email-jlayton@redhat.com> X-Scanned-By: MIMEDefang 2.67 on 10.5.11.11 Sender: linux-cifs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org X-Spam-Status: No, score=-8.4 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Since we always hold the i_lock when inserting a new waiter onto the fl_block list, we can avoid taking the global lock at all if we find that it's empty when we go to wake up blocked waiters. Signed-off-by: Jeff Layton --- fs/locks.c | 15 ++++++++++++++- 1 files changed, 14 insertions(+), 1 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index ce302d4..84e269f 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -548,7 +548,10 @@ static void locks_delete_block(struct file_lock *waiter) * the order they blocked. The documentation doesn't require this but * it seems like the reasonable thing to do. * - * Must be called with file_lock_lock held! + * Must be called with both the i_lock and file_lock_lock held. The fl_block + * list itself is protected by the file_lock_list, but by ensuring that the + * i_lock is also held on insertions we can avoid taking the file_lock_lock + * in some cases when we see that the fl_block list is empty. */ static void __locks_insert_block(struct file_lock *blocker, struct file_lock *waiter) @@ -576,6 +579,16 @@ static void locks_insert_block(struct file_lock *blocker, */ static void locks_wake_up_blocks(struct file_lock *blocker) { + /* + * Avoid taking global lock if list is empty. This is safe since new + * blocked requests are only added to the list under the i_lock, and + * the i_lock is always held here. Note that removal from the fl_block + * list does not require the i_lock, so we must recheck list_empty() + * after acquiring the file_lock_lock. + */ + if (list_empty(&blocker->fl_block)) + return; + spin_lock(&file_lock_lock); while (!list_empty(&blocker->fl_block)) { struct file_lock *waiter;