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Mon, 7 Jun 2021 18:31:41 -0700 Received: by devvm3388.prn0.facebook.com (Postfix, from userid 111017) id 88F2A81D6D41; Mon, 7 Jun 2021 18:31:29 -0700 (PDT) From: Roman Gushchin To: Jan Kara , Tejun Heo CC: , , , Alexander Viro , Dennis Zhou , Dave Chinner , , Roman Gushchin Subject: [PATCH v8 0/8] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups Date: Mon, 7 Jun 2021 18:31:15 -0700 Message-ID: <20210608013123.1088882-1-guro@fb.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: Gy4FPVrJar44j45KcKCTlSYXo5YfaB-2 X-Proofpoint-ORIG-GUID: Gy4FPVrJar44j45KcKCTlSYXo5YfaB-2 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-06-08_01:2021-06-04,2021-06-08 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 impostorscore=0 lowpriorityscore=0 adultscore=0 mlxscore=0 phishscore=0 mlxlogscore=289 suspectscore=0 clxscore=1015 bulkscore=0 malwarescore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106080007 X-FB-Internal: deliver Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=fb.com header.s=facebook header.b=Htd5yLtP; spf=pass (imf09.hostedemail.com: domain of "prvs=5793bd417c=guro@fb.com" designates 67.231.145.42 as permitted sender) smtp.mailfrom="prvs=5793bd417c=guro@fb.com"; dmarc=pass (policy=reject) header.from=fb.com X-Stat-Signature: mknnnyksjeufoipa4dnmh9hxm59g5g6z X-Rspamd-Queue-Id: F21306000103 X-Rspamd-Server: rspam06 X-HE-Tag: 1623115902-279982 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: 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 and switching is performed from a work context. Big thanks to Jan Kara, Dennis Zhou, Hillf Danton and Tejun Heo for their ideas and contribution to this patchset. v8: - switch inodes to a nearest living ancestor wb instead of root wb - added two inodes switching fixes suggested by Jan Kara v7: - shared locking for multiple inode switching - introduced inode_prepare_wbs_switch() helper - extended the pre-switch inode check for I_WILL_FREE - added comments here and there v6: - extended and reused wbs switching functionality to switch inodes on cgwb cleanup - fixed offline_list handling - switched to the unbound_wq - other minor fixes 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 (8): writeback, cgroup: do not switch inodes with I_WILL_FREE flag writeback, cgroup: add smp_mb() to cgroup_writeback_umount() writeback, cgroup: increment isw_nr_in_flight before grabbing an inode writeback, cgroup: switch to rcu_work API in inode_switch_wbs() writeback, cgroup: keep list of inodes attached to bdi_writeback writeback, cgroup: split out the functional part of inode_switch_wbs_work_fn() writeback, cgroup: support switching multiple inodes at once writeback, cgroup: release dying cgwbs by switching attached inodes fs/fs-writeback.c | 323 +++++++++++++++++++++---------- include/linux/backing-dev-defs.h | 20 +- include/linux/writeback.h | 1 + mm/backing-dev.c | 69 ++++++- 4 files changed, 312 insertions(+), 101 deletions(-)