From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id B81BE6B0025 for ; Wed, 21 Mar 2018 13:17:03 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id 2so2973171pft.4 for ; Wed, 21 Mar 2018 10:17:03 -0700 (PDT) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com. [115.124.30.130]) by mx.google.com with ESMTPS id b4si2968358pgq.427.2018.03.21.10.17.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 21 Mar 2018 10:17:02 -0700 (PDT) Subject: Re: [RFC PATCH 1/8] mm: mmap: unmap large mapping by section From: Yang Shi References: <1521581486-99134-1-git-send-email-yang.shi@linux.alibaba.com> <1521581486-99134-2-git-send-email-yang.shi@linux.alibaba.com> <20180321131449.GN23100@dhcp22.suse.cz> <8e0ded7b-4be4-fa25-f40c-d3116a6db4db@linux.alibaba.com> Message-ID: Date: Wed, 21 Mar 2018 10:16:41 -0700 MIME-Version: 1.0 In-Reply-To: <8e0ded7b-4be4-fa25-f40c-d3116a6db4db@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 3/21/18 9:50 AM, Yang Shi wrote: > > > On 3/21/18 6:14 AM, Michal Hocko wrote: >> On Wed 21-03-18 05:31:19, Yang Shi wrote: >>> When running some mmap/munmap scalability tests with large memory (i.e. >>>> 300GB), the below hung task issue may happen occasionally. >>> INFO: task ps:14018 blocked for more than 120 seconds. >>> Tainted: G E 4.9.79-009.ali3000.alios7.x86_64 #1 >>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this >>> message. >>> ps D 0 14018 1 0x00000004 >>> ffff885582f84000 ffff885e8682f000 ffff880972943000 ffff885ebf499bc0 >>> ffff8828ee120000 ffffc900349bfca8 ffffffff817154d0 0000000000000040 >>> 00ffffff812f872a ffff885ebf499bc0 024000d000948300 ffff880972943000 >>> Call Trace: >>> [] ? __schedule+0x250/0x730 >>> [] schedule+0x36/0x80 >>> [] rwsem_down_read_failed+0xf0/0x150 >>> [] call_rwsem_down_read_failed+0x18/0x30 >>> [] down_read+0x20/0x40 >>> [] proc_pid_cmdline_read+0xd9/0x4e0 >> Slightly off-topic: >> Btw. this sucks as well. Do we really need to take mmap_sem here? Do any >> of >> arg_start = mm->arg_start; >> arg_end = mm->arg_end; >> env_start = mm->env_start; >> env_end = mm->env_end; >> >> change after exec or while the pid is already visible in proc? If yes >> maybe we can use a dedicated lock. BTW, this is not the only place to acquire mmap_sem in proc_pid_cmdline_read(), it calls access_remote_vm() which need acquire mmap_sem too, so the mmap_sem scalability issue will be hit sooner or later. Yang > > Actually, Alexey Dobriyan had the same comment when he reviewed my > very first patch (which changes down_read to down_read_killable at > that place). > > Those 4 values might be changed by prctl_set_mm() and > prctl_set_mm_map() concurrently. They used to use down_read() to > protect the change, but it looks not good enough to protect concurrent > writing. So, Mateusz Guzik's commit > ddf1d398e517e660207e2c807f76a90df543a217 ("prctl: take mmap sem for > writing to protect against others") change it to down_write(). > > It seems mmap_sem can be replaced to a dedicated lock. How about > defining a rwlock in mm_struct to protect those data? I will come up > with a RFC patch for this. > > However, this dedicated lock just can work around this specific case. > I believe solving mmap_sem scalability issue aimed by the patch series > is still our consensus. > > Thanks, > Yang > > > >