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[95.108.205.193]) by mx.google.com with ESMTPS id z4si30232701lfj.82.2019.07.22.02.36.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 Jul 2019 02:36:10 -0700 (PDT) Received-SPF: pass (google.com: domain of khlebnikov@yandex-team.ru designates 95.108.205.193 as permitted sender) client-ip=95.108.205.193; Authentication-Results: mx.google.com; dkim=pass header.i=@yandex-team.ru header.s=default header.b=C4FclbtD; spf=pass (google.com: domain of khlebnikov@yandex-team.ru designates 95.108.205.193 as permitted sender) smtp.mailfrom=khlebnikov@yandex-team.ru; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=yandex-team.ru 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP 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 Reviewed-by: Jan Kara --- 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);