From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756218AbeDZNHJ (ORCPT ); Thu, 26 Apr 2018 09:07:09 -0400 Received: from mx2.suse.de ([195.135.220.15]:36137 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755671AbeDZNHE (ORCPT ); Thu, 26 Apr 2018 09:07:04 -0400 Date: Thu, 26 Apr 2018 15:07:00 +0200 From: Michal Hocko To: Kirill Tkhai Cc: 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, ebiederm@xmission.com, dhowells@redhat.com, rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable Message-ID: <20180426130700.GP17484@dhcp22.suse.cz> References: <152473763015.29458.1131542311542381803.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <152473763015.29458.1131542311542381803.stgit@localhost.localdomain> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Michal Hocko SUSE Labs