From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751398AbeFABH7 (ORCPT ); Thu, 31 May 2018 21:07:59 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:37340 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751343AbeFABHy (ORCPT ); Thu, 31 May 2018 21:07:54 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Michal Hocko Cc: Kirill Tkhai , akpm@linux-foundation.org, peterz@infradead.org, oleg@redhat.com, viro@zeniv.linux.org.uk, mingo@kernel.org, paulmck@linux.vnet.ibm.com, keescook@chromium.org, riel@redhat.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, marcos.souza.org@gmail.com, hoeun.ryu@gmail.com, pasha.tatashin@oracle.com, gs051095@gmail.com, dhowells@redhat.com, rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org References: <152473763015.29458.1131542311542381803.stgit@localhost.localdomain> <20180426130700.GP17484@dhcp22.suse.cz> Date: Thu, 31 May 2018 20:07:28 -0500 In-Reply-To: <20180426130700.GP17484@dhcp22.suse.cz> (Michal Hocko's message of "Thu, 26 Apr 2018 15:07:00 +0200") Message-ID: <877enj9uwf.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1fOYXW-0003eo-UJ;;;mid=<877enj9uwf.fsf@xmission.com>;;;hst=in01.mta.xmission.com;;;ip=97.119.124.205;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+j1zZ1Uv3mYOBfdKuywxLKMqRWQwqN+cU= X-SA-Exim-Connect-IP: 97.119.124.205 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 TVD_RCVD_IP Message was received from an IP address * 0.5 XMGappySubj_01 Very gappy subject * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.7 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa07 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_03 6+ unique symbols in subject * 0.0 T_TooManySym_01 4+ unique symbols in subject * 0.0 T_TooManySym_02 5+ unique symbols in subject X-Spam-DCC: XMission; sa07 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **;Michal Hocko X-Spam-Relay-Country: X-Spam-Timing: total 15017 ms - load_scoreonly_sql: 0.03 (0.0%), signal_user_changed: 2.5 (0.0%), b_tie_ro: 1.75 (0.0%), parse: 0.71 (0.0%), extract_message_metadata: 2.4 (0.0%), get_uri_detail_list: 0.94 (0.0%), tests_pri_-1000: 2.9 (0.0%), tests_pri_-950: 1.15 (0.0%), tests_pri_-900: 0.97 (0.0%), tests_pri_-400: 22 (0.1%), check_bayes: 21 (0.1%), b_tokenize: 6 (0.0%), b_tok_get_all: 8 (0.1%), b_comp_prob: 1.94 (0.0%), b_tok_touch_all: 3.6 (0.0%), b_finish: 0.49 (0.0%), tests_pri_0: 172 (1.1%), check_dkim_signature: 0.46 (0.0%), check_dkim_adsp: 3.0 (0.0%), tests_pri_500: 14806 (98.6%), poll_dns_idle: 14799 (98.5%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michal Hocko writes: > On Thu 26-04-18 14:00:19, Kirill Tkhai wrote: >> This function searches for a new mm owner in children and siblings, >> and then iterates over all processes in the system in unlikely case. >> Despite the case is unlikely, its probability growths with the number >> of processes in the system. The time, spent on iterations, also growths. >> I regulary observe mm_update_next_owner() in crash dumps (not related >> to this function) of the nodes with many processes (20K+), so it looks >> like it's not so unlikely case. > > Did you manage to find the pattern that forces mm_update_next_owner to > slow paths? This really shouldn't trigger very often. If we can fallback > easily then I suspect that we should be better off reconsidering > mm->owner and try to come up with something more clever. I've had a > patch to remove owner few years back. It needed some work to finish but > maybe that would be a better than try to make non-scalable thing suck > less. Reading through the code I just found a trivial pattern that triggers this. Create a multi-threaded process. Have the thread group leader (the first thread) exit. This has the potential to be a significant DOS attack if anyone cares. Eric