From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752973AbeFAOeO (ORCPT ); Fri, 1 Jun 2018 10:34:14 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:40156 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752691AbeFAOdG (ORCPT ); Fri, 1 Jun 2018 10:33:06 -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> <877enj9uwf.fsf@xmission.com> <20180601135725.GE15278@dhcp22.suse.cz> Date: Fri, 01 Jun 2018 09:32:42 -0500 In-Reply-To: <20180601135725.GE15278@dhcp22.suse.cz> (Michal Hocko's message of "Fri, 1 Jun 2018 15:57:25 +0200") Message-ID: <87a7sey3ud.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=1fOl6l-0007xK-8w;;;mid=<87a7sey3ud.fsf@xmission.com>;;;hst=in01.mta.xmission.com;;;ip=97.119.124.205;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1975ZT+vYGh4y1VMRXuQeJYUtsLELeAhr0= 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 15027 ms - load_scoreonly_sql: 0.04 (0.0%), signal_user_changed: 3.1 (0.0%), b_tie_ro: 2.2 (0.0%), parse: 1.18 (0.0%), extract_message_metadata: 4.7 (0.0%), get_uri_detail_list: 2.4 (0.0%), tests_pri_-1000: 4.5 (0.0%), tests_pri_-950: 1.64 (0.0%), tests_pri_-900: 1.44 (0.0%), tests_pri_-400: 30 (0.2%), check_bayes: 29 (0.2%), b_tokenize: 12 (0.1%), b_tok_get_all: 8 (0.1%), b_comp_prob: 3.7 (0.0%), b_tok_touch_all: 2.8 (0.0%), b_finish: 0.57 (0.0%), tests_pri_0: 243 (1.6%), check_dkim_signature: 0.69 (0.0%), check_dkim_adsp: 3.2 (0.0%), tests_pri_500: 14725 (98.0%), poll_dns_idle: 14716 (97.9%), 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 31-05-18 20:07:28, Eric W. Biederman wrote: >> 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. > > Hmm, I thought that we try to iterate over threads in the same thread > group first. But we are not doing that. Anyway just CLONE_VM without > CLONE_THREAD would achieve the same pathological path but that should be > rare. Yes, if the child exited. The code searches the children and siblings but the parents of the process that exited. > Group leader exiting early without tearing down the whole thread > group should be quite rare as well. No question that somebody might do > that on purpose though... The group leader exiting early is a completely legitimate and reasonable thing to do, even if it is rare. I think all it would take is one program like that in a work-load for the performance to descend into something unpleasant. Eric