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 X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 93649C76198 for ; Mon, 22 Jul 2019 09:43:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63AB72190F for ; Mon, 22 Jul 2019 09:43:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=yandex-team.ru header.i=@yandex-team.ru header.b="C4FclbtD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728743AbfGVJnm (ORCPT ); Mon, 22 Jul 2019 05:43:42 -0400 Received: from forwardcorp1o.mail.yandex.net ([95.108.205.193]:35528 "EHLO forwardcorp1o.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728021AbfGVJnl (ORCPT ); Mon, 22 Jul 2019 05:43:41 -0400 X-Greylist: delayed 449 seconds by postgrey-1.27 at vger.kernel.org; Mon, 22 Jul 2019 05:43:40 EDT Received: from mxbackcorp2j.mail.yandex.net (mxbackcorp2j.mail.yandex.net [IPv6:2a02:6b8:0:1619::119]) by forwardcorp1o.mail.yandex.net (Yandex) with ESMTP id 8EF252E1251; Mon, 22 Jul 2019 12:36:09 +0300 (MSK) Received: from smtpcorp1o.mail.yandex.net (smtpcorp1o.mail.yandex.net [2a02:6b8:0:1a2d::30]) by mxbackcorp2j.mail.yandex.net (nwsmtp/Yandex) with ESMTP id piK2rewsgT-a8Nmo53U; Mon, 22 Jul 2019 12:36:09 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1563788169; bh=DL5UzA+B5XRB4qh0F2iWC5P1iVbcg0/rElIhEVtbXfg=; h=Message-ID:Date:To:From:Subject:Cc; b=C4FclbtDQ5b7smwavzXfTwnAGBDtyvoKz3qJxF/M76PisgHI1mGKIvG4cGohU069H I+8pkq99Gy18EG8atUE+4MtHJf7ZK+4vWOcIFCuhSSGHIaGhFtECkYzI0ajGXe82Ox ixtwBZaI7SGYRKn+koCY2zzBmM5SBCVGXhL8BdLI= Authentication-Results: mxbackcorp2j.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from dynamic-red.dhcp.yndx.net (dynamic-red.dhcp.yndx.net [2a02:6b8:0:40c:38b3:1cdf:ad1a:1fe1]) by smtpcorp1o.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id tCVKM0ss34-a8I48tMX; Mon, 22 Jul 2019 12:36:08 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) Subject: [PATCH 1/2] mm/filemap: don't initiate writeback if mapping has no dirty pages From: Konstantin Khlebnikov To: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org Cc: Tejun Heo , Jens Axboe , Johannes Weiner Date: Mon, 22 Jul 2019 12:36:08 +0300 Message-ID: <156378816804.1087.8607636317907921438.stgit@buzz> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Functions like filemap_write_and_wait_range() should do nothing if inode has no dirty pages or pages currently under writeback. But they anyway construct struct writeback_control and this does some atomic operations if CONFIG_CGROUP_WRITEBACK=y - on fast path it locks inode->i_lock and updates state of writeback ownership, on slow path might be more work. Current this path is safely avoided only when inode mapping has no pages. For example generic_file_read_iter() calls filemap_write_and_wait_range() at each O_DIRECT read - pretty hot path. This patch skips starting new writeback if mapping has no dirty tags set. If writeback is already in progress filemap_write_and_wait_range() will wait for it. Signed-off-by: Konstantin Khlebnikov --- mm/filemap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index d0cf700bf201..d9572593e5c7 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -408,7 +408,8 @@ int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start, .range_end = end, }; - if (!mapping_cap_writeback_dirty(mapping)) + if (!mapping_cap_writeback_dirty(mapping) || + !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) return 0; wbc_attach_fdatawrite_inode(&wbc, mapping->host);