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[2a02:6b8:0:1472:2741:0:8b6:217]) by mx.google.com with ESMTPS id d26si29660937ljj.123.2019.07.19.10.46.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Jul 2019 10:46:37 -0700 (PDT) Received-SPF: pass (google.com: domain of khlebnikov@yandex-team.ru designates 2a02:6b8:0:1472:2741:0:8b6:217 as permitted sender) client-ip=2a02:6b8:0:1472:2741:0:8b6:217; Authentication-Results: mx.google.com; dkim=pass header.i=@yandex-team.ru header.s=default header.b=G9TOwr2r; spf=pass (google.com: domain of khlebnikov@yandex-team.ru designates 2a02:6b8:0:1472:2741:0:8b6:217 as permitted sender) smtp.mailfrom=khlebnikov@yandex-team.ru; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=yandex-team.ru Received: from mxbackcorp1g.mail.yandex.net (mxbackcorp1g.mail.yandex.net [IPv6:2a02:6b8:0:1402::301]) by forwardcorp1p.mail.yandex.net (Yandex) with ESMTP id F1AE52E09F4; Fri, 19 Jul 2019 20:46:36 +0300 (MSK) Received: from smtpcorp1o.mail.yandex.net (smtpcorp1o.mail.yandex.net [2a02:6b8:0:1a2d::30]) by mxbackcorp1g.mail.yandex.net (nwsmtp/Yandex) with ESMTP id ICah43fs8W-kamGWXC8; Fri, 19 Jul 2019 20:46:36 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1563558396; bh=1Z3L2rCQwZ1u7nVoekpSRwgzFoMR8NsFTnt2HHesBaM=; h=Message-ID:Date:To:From:Subject; b=G9TOwr2rBmfREw3RPgVRGhOib+9KfKfXg7eGJs92C82XO+TzZdmfUlsdu83GtwFP2 Owe7Ncyh2YWSmj+VLAMHq0GEUgfLLCzsgU6lS4EgQ+/5Rp09NDlCi8dyT67snEocI/ Ej2WIi+3xDW5HS6wtiZQm1tCkBz1HU6MULzYQ6c8= Authentication-Results: mxbackcorp1g.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:38d2:81d0:9f31:221f]) by smtpcorp1o.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id C9SHlfdlgB-kZIGxdaN; Fri, 19 Jul 2019 20:46:35 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) Subject: [PATCH] cgroup writeback: use online cgroup when switching from dying bdi_writebacks From: Konstantin Khlebnikov To: Jens Axboe , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org, Tejun Heo , cgroups@vger.kernel.org Date: Fri, 19 Jul 2019 20:46:35 +0300 Message-ID: <156355839560.2063.5265687291430814589.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 Offline memory cgroups forbids creation new bdi_writebacks. Each try wastes cpu cycles and increases contention around cgwb_lock. For example each O_DIRECT read calls filemap_write_and_wait_range() if inode has cached pages which tries to switch from dying writeback. This patch switches inode writeback to closest online parent cgroup. Fixes: e8a7abf5a5bd ("writeback: disassociate inodes from dying bdi_writebacks") Signed-off-by: Konstantin Khlebnikov --- fs/fs-writeback.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 542b02d170f8..3af44591a106 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -505,7 +505,7 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) /* find and pin the new wb */ rcu_read_lock(); memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys); - if (memcg_css) + if (memcg_css && (memcg_css->flags & CSS_ONLINE)) isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); rcu_read_unlock(); if (!isw->new_wb) @@ -579,9 +579,16 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc, /* * A dying wb indicates that the memcg-blkcg mapping has changed * and a new wb is already serving the memcg. Switch immediately. + * If memory cgroup is offline switch to closest online parent. */ - if (unlikely(wb_dying(wbc->wb))) - inode_switch_wbs(inode, wbc->wb_id); + if (unlikely(wb_dying(wbc->wb))) { + struct cgroup_subsys_state *memcg_css = wbc->wb->memcg_css; + + while (!(memcg_css->flags & CSS_ONLINE)) + memcg_css = memcg_css->parent; + + inode_switch_wbs(inode, memcg_css->id); + } } EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);