From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id 537908E00E5 for ; Wed, 12 Dec 2018 04:42:57 -0500 (EST) Received: by mail-pf1-f199.google.com with SMTP id q63so14963682pfi.19 for ; Wed, 12 Dec 2018 01:42:57 -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 a96sor25043773pla.29.2018.12.12.01.42.55 for (Google Transport Security); Wed, 12 Dec 2018 01:42:55 -0800 (PST) Date: Wed, 12 Dec 2018 12:42:49 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mm, memcg: fix reclaim deadlock with writeback Message-ID: <20181212094249.cw4xjrdchqsp2tkt@kshutemo-mobl1> References: <20181211132645.31053-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181211132645.31053-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Liu Bo , Jan Kara , Dave Chinner , Theodore Ts'o , Johannes Weiner , Vladimir Davydov , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, LKML , Michal Hocko , Hugh Dickins On Tue, Dec 11, 2018 at 02:26:45PM +0100, 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. Side node: Do we have PG_writeback vs. PG_locked ordering documentated somewhere? IIUC, the trace from task2 suggests that we must not wait for writeback on the locked page. But that not what I see for many wait_on_page_writeback() users: it usally called with the page locked. I see it for truncate, shmem, swapfile, splice... Maybe the problem is within task2 codepath after all? -- Kirill A. Shutemov