From patchwork Wed May 26 22:25:55 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roman Gushchin X-Patchwork-Id: 12282833 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=-14.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 67556C4708B for ; Wed, 26 May 2021 22:26:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2B212613D3 for ; Wed, 26 May 2021 22:26:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234353AbhEZW1j (ORCPT ); Wed, 26 May 2021 18:27:39 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:58202 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233535AbhEZW1g (ORCPT ); Wed, 26 May 2021 18:27:36 -0400 Received: from pps.filterd (m0148460.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 14QMF7gu019599 for ; Wed, 26 May 2021 15:26:04 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : mime-version : content-transfer-encoding : content-type; s=facebook; bh=m2Usb8pBnaJ5JSG5ZmqsO2PX6YX/Fcc3JtrbDbrn2J0=; b=KdozIGjxtdV16VDlebccLJllHB/zniP9jY3DhAld5mU9GLWGdhf3kZaoO5kOGPJRY8kh jNbnoEJrtEhRXaPGxoMaan0dLQiIpnFSPcI6Lfh/2PqW+J4sKIdSBlGt9OfUtcsKDWoA aSqcZSNH0A4aJQB/Vdp+AG/T94NDmp7SzKY= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 38shgsmygb-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 26 May 2021 15:26:04 -0700 Received: from intmgw003.48.prn1.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:82::c) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Wed, 26 May 2021 15:26:03 -0700 Received: by devvm3388.prn0.facebook.com (Postfix, from userid 111017) id A2E5A7B6ABB3; Wed, 26 May 2021 15:25:58 -0700 (PDT) From: Roman Gushchin To: Jan Kara , Tejun Heo CC: , , , Alexander Viro , Dennis Zhou , Dave Chinner , , Roman Gushchin Subject: [PATCH v5 0/2] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups Date: Wed, 26 May 2021 15:25:55 -0700 Message-ID: <20210526222557.3118114-1-guro@fb.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: pnE_48lbiGrgoJMQMhMXA1i7bGTi2mT7 X-Proofpoint-ORIG-GUID: pnE_48lbiGrgoJMQMhMXA1i7bGTi2mT7 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-05-26_12:2021-05-26,2021-05-26 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 adultscore=0 mlxscore=0 mlxlogscore=528 impostorscore=0 malwarescore=0 clxscore=1015 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2105260151 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org When an inode is getting dirty for the first time it's associated with a wb structure (see __inode_attach_wb()). It can later be switched to another wb (if e.g. some other cgroup is writing a lot of data to the same inode), but otherwise stays attached to the original wb until being reclaimed. The problem is that the wb structure holds a reference to the original memory and blkcg cgroups. So if an inode has been dirty once and later is actively used in read-only mode, it has a good chance to pin down the original memory and blkcg cgroups forewer. This is often the case with services bringing data for other services, e.g. updating some rpm packages. In the real life it becomes a problem due to a large size of the memcg structure, which can easily be 1000x larger than an inode. Also a really large number of dying cgroups can raise different scalability issues, e.g. making the memory reclaim costly and less effective. To solve the problem inodes should be eventually detached from the corresponding writeback structure. It's inefficient to do it after every writeback completion. Instead it can be done whenever the original memory cgroup is offlined and writeback structure is getting killed. Scanning over a (potentially long) list of inodes and detach them from the writeback structure can take quite some time. To avoid scanning all inodes, attached inodes are kept on a new list (b_attached). To make it less noticeable to a user, the scanning is performed from a work context. Big thanks to Jan Kara and Dennis Zhou for their ideas and contribution to the previous iterations of this patch. v5: - switch inodes to bdi->wb instead of zeroing inode->i_wb - split the single patch into two - only cgwbs maintain lists of attached inodes - added cond_resched() - fixed !CONFIG_CGROUP_WRITEBACK handling - extended list of prohibited inodes flag - other small fixes Roman Gushchin (2): writeback, cgroup: keep list of inodes attached to bdi_writeback writeback, cgroup: release dying cgwbs by switching attached inodes fs/fs-writeback.c | 101 +++++++++++++++++++++++++------ include/linux/backing-dev-defs.h | 2 + include/linux/backing-dev.h | 7 +++ include/linux/writeback.h | 2 + mm/backing-dev.c | 63 ++++++++++++++++++- 5 files changed, 156 insertions(+), 19 deletions(-)