From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw1-f70.google.com (mail-yw1-f70.google.com [209.85.161.70]) by kanga.kvack.org (Postfix) with ESMTP id 95CE18E00E5 for ; Wed, 12 Dec 2018 12:24:58 -0500 (EST) Received: by mail-yw1-f70.google.com with SMTP id q82so11030762ywg.22 for ; Wed, 12 Dec 2018 09:24:58 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id s187sor2500099ywd.157.2018.12.12.09.24.57 for (Google Transport Security); Wed, 12 Dec 2018 09:24:57 -0800 (PST) MIME-Version: 1.0 References: <20181211132645.31053-1-mhocko@kernel.org> <20181212155055.1269-1-mhocko@kernel.org> In-Reply-To: <20181212155055.1269-1-mhocko@kernel.org> From: Shakeel Butt Date: Wed, 12 Dec 2018 09:24:45 -0800 Message-ID: Subject: Re: [PATCH v2] mm, memcg: fix reclaim deadlock with writeback Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , "Kirill A. Shutemov" , bo.liu@linux.alibaba.com, Jan Kara , david@fromorbit.com, tytso@mit.edu, Johannes Weiner , Vladimir Davydov , Linux MM , linux-fsdevel , LKML , Michal Hocko On Wed, Dec 12, 2018 at 7:51 AM Michal Hocko wrote: > > From: Michal Hocko > > Liu Bo has experienced a deadlock between memcg (legacy) reclaim and the > ext4 writeback > task1: > [] wait_on_page_bit+0x82/0xa0 > [] shrink_page_list+0x907/0x960 > [] shrink_inactive_list+0x2c7/0x680 > [] shrink_node_memcg+0x404/0x830 > [] shrink_node+0xd8/0x300 > [] do_try_to_free_pages+0x10d/0x330 > [] try_to_free_mem_cgroup_pages+0xd5/0x1b0 > [] try_charge+0x14d/0x720 > [] memcg_kmem_charge_memcg+0x3c/0xa0 > [] memcg_kmem_charge+0x7e/0xd0 > [] __alloc_pages_nodemask+0x178/0x260 > [] alloc_pages_current+0x95/0x140 > [] pte_alloc_one+0x17/0x40 > [] __pte_alloc+0x1e/0x110 > [] alloc_set_pte+0x5fe/0xc20 > [] do_fault+0x103/0x970 > [] handle_mm_fault+0x61e/0xd10 > [] __do_page_fault+0x252/0x4d0 > [] do_page_fault+0x30/0x80 > [] page_fault+0x28/0x30 > [] 0xffffffffffffffff > > task2: > [] __lock_page+0x86/0xa0 > [] mpage_prepare_extent_to_map+0x2e7/0x310 [ext4] > [] ext4_writepages+0x479/0xd60 > [] do_writepages+0x1e/0x30 > [] __writeback_single_inode+0x45/0x320 > [] writeback_sb_inodes+0x272/0x600 > [] __writeback_inodes_wb+0x92/0xc0 > [] wb_writeback+0x268/0x300 > [] wb_workfn+0xb4/0x390 > [] process_one_work+0x189/0x420 > [] worker_thread+0x4e/0x4b0 > [] kthread+0xe6/0x100 > [] ret_from_fork+0x41/0x50 > [] 0xffffffffffffffff > > He adds > : task1 is waiting for the PageWriteback bit of the page that task2 has > : collected in mpd->io_submit->io_bio, and tasks2 is waiting for the LOCKED > : bit the page which tasks1 has locked. > > More precisely task1 is handling a page fault and it has a page locked > while it charges a new page table to a memcg. That in turn hits a memory > limit reclaim and the memcg reclaim for legacy controller is waiting on > the writeback but that is never going to finish because the writeback > itself is waiting for the page locked in the #PF path. So this is > essentially ABBA deadlock. > > Waiting for the writeback in legacy memcg controller is a workaround > for pre-mature OOM killer invocations because there is no dirty IO > throttling available for the controller. There is no easy way around > that unfortunately. Therefore fix this specific issue by pre-allocating > the page table outside of the page lock. We have that handy > infrastructure for that already so simply reuse the fault-around pattern > which already does this. Michal, can you please add the following para in the commit message as well which was in the first version. This fact should be documented at least in the commit message. > > There are probably other hidden __GFP_ACCOUNT | GFP_KERNEL allocations > from under a fs page locked but they should be really rare. I am not > aware of a better solution unfortunately. > thanks, Shakeel