From patchwork Mon Apr 6 19:58:22 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 6165021 Return-Path: X-Original-To: patchwork-linux-fsdevel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 100B0BF4A6 for ; Mon, 6 Apr 2015 20:14:19 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 2842820303 for ; Mon, 6 Apr 2015 20:14:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27BCD202EC for ; Mon, 6 Apr 2015 20:14:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753872AbbDFUOP (ORCPT ); Mon, 6 Apr 2015 16:14:15 -0400 Received: from mail-qk0-f176.google.com ([209.85.220.176]:36257 "EHLO mail-qk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753406AbbDFT7t (ORCPT ); Mon, 6 Apr 2015 15:59:49 -0400 Received: by qku63 with SMTP id 63so30980321qku.3; Mon, 06 Apr 2015 12:59:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=nu1iPuMX5jMZ6CGHGwlyy54DMxNLC2l6kTthI8anOFg=; b=s88Lc4MB9YA1dot33Pk2nnrqldiOYhihRxE7Wm7278mW4EQlQEOH9XwmqXHHNBx4e4 +XibM19VqYSgAG2AWmsSkHIaWBKRnRv7bEvPfIqHaXSfjVa0ZupX5d/RT/RDZffRH8Mu +02OI91sdiOkBvkQBGdcTb1H5RbKp8+IwuJAdqJZa9jX7BJPFfZ8cGO2Ke91hjwmLi2i aRmtNud2Spx9gUA8sxzNpbirYZZKf1QvhzOhLXp4wacQy4RghUAfZeiQRqUoaxSBNZdU 6NDIufvJLU91MBnhHpkTXR6YewCwyQlp2OODrUSk/F1NZkAoyDHiQjwkn8G2TxCp5s24 jKyA== X-Received: by 10.55.21.31 with SMTP id f31mr31599901qkh.95.1428350388184; Mon, 06 Apr 2015 12:59:48 -0700 (PDT) Received: from htj.duckdns.org.lan (207-38-238-8.c3-0.wsd-ubr1.qens-wsd.ny.cable.rcn.com. [207.38.238.8]) by mx.google.com with ESMTPSA id z67sm3914418qgz.10.2015.04.06.12.59.46 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 Apr 2015 12:59:47 -0700 (PDT) From: Tejun Heo To: axboe@kernel.dk Cc: linux-kernel@vger.kernel.org, jack@suse.cz, hch@infradead.org, hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, vgoyal@redhat.com, lizefan@huawei.com, cgroups@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.cz, clm@fb.com, fengguang.wu@intel.com, david@fromorbit.com, gthelen@google.com, Tejun Heo Subject: [PATCH 33/49] writeback: don't issue wb_writeback_work if clean Date: Mon, 6 Apr 2015 15:58:22 -0400 Message-Id: <1428350318-8215-34-git-send-email-tj@kernel.org> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1428350318-8215-1-git-send-email-tj@kernel.org> References: <1428350318-8215-1-git-send-email-tj@kernel.org> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Spam-Status: No, score=-6.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_HI,T_DKIM_INVALID,T_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 There are several places in fs/fs-writeback.c which queues wb_writeback_work without checking whether the target wb (bdi_writeback) has dirty inodes or not. The only thing wb_writeback_work does is writing back the dirty inodes for the target wb and queueing a work item for a clean wb is essentially noop. There are some side effects such as bandwidth stats being updated and triggering tracepoints but these don't affect the operation in any meaningful way. This patch makes all writeback_inodes_sb_nr() and sync_inodes_sb() skip wb_queue_work() if the target bdi is clean. Also, it moves dirtiness check from wakeup_flusher_threads() to __wb_start_writeback() so that all its callers benefit from the check. While the overhead incurred by scheduling a noop work isn't currently significant, the overhead may be higher with cgroup writeback support as we may end up issuing noop work items to a lot of clean wb's. Signed-off-by: Tejun Heo Cc: Jens Axboe Cc: Jan Kara --- fs/fs-writeback.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 5df1bc7..6720af9 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -177,6 +177,9 @@ static void __wb_start_writeback(struct bdi_writeback *wb, long nr_pages, { struct wb_writeback_work *work; + if (!wb_has_dirty_io(wb)) + return; + /* * This is WB_SYNC_NONE writeback, so if allocation fails just * wakeup the thread for old dirty data writeback @@ -1197,11 +1200,8 @@ void wakeup_flusher_threads(long nr_pages, enum wb_reason reason) nr_pages = get_nr_dirty_pages(); rcu_read_lock(); - list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) { - if (!bdi_has_dirty_io(bdi)) - continue; + list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) __wb_start_writeback(&bdi->wb, nr_pages, false, reason); - } rcu_read_unlock(); } @@ -1435,11 +1435,12 @@ void writeback_inodes_sb_nr(struct super_block *sb, .nr_pages = nr, .reason = reason, }; + struct backing_dev_info *bdi = sb->s_bdi; - if (sb->s_bdi == &noop_backing_dev_info) + if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info) return; WARN_ON(!rwsem_is_locked(&sb->s_umount)); - wb_queue_work(&sb->s_bdi->wb, &work); + wb_queue_work(&bdi->wb, &work); wait_for_completion(&done); } EXPORT_SYMBOL(writeback_inodes_sb_nr); @@ -1517,13 +1518,14 @@ void sync_inodes_sb(struct super_block *sb) .reason = WB_REASON_SYNC, .for_sync = 1, }; + struct backing_dev_info *bdi = sb->s_bdi; /* Nothing to do? */ - if (sb->s_bdi == &noop_backing_dev_info) + if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info) return; WARN_ON(!rwsem_is_locked(&sb->s_umount)); - wb_queue_work(&sb->s_bdi->wb, &work); + wb_queue_work(&bdi->wb, &work); wait_for_completion(&done); wait_sb_inodes(sb);