Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751761AbdFOA2V (ORCPT ); Wed, 14 Jun 2017 20:28:21 -0400 Received: from mail-pf0-f179.google.com ([209.85.192.179]:36728 "EHLO mail-pf0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750768AbdFOA2T (ORCPT ); Wed, 14 Jun 2017 20:28:19 -0400 Date: Wed, 14 Jun 2017 17:28:16 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Michal Hocko cc: Matthew Wilcox , Vlastimil Babka , Larry Finger , Andrew Morton , LKML , linux-mm@kvack.org Subject: Re: Sleeping BUG in khugepaged for i586 In-Reply-To: <20170612062918.GA4145@dhcp22.suse.cz> Message-ID: References: <1e883924-9766-4d2a-936c-7a49b337f9e2@lwfinger.net> <9ab81c3c-e064-66d2-6e82-fc9bac125f56@suse.cz> <20170608144831.GA19903@dhcp22.suse.cz> <20170608170557.GA8118@bombadil.infradead.org> <20170608201822.GA5535@dhcp22.suse.cz> <20170608203046.GB5535@dhcp22.suse.cz> <20170610080941.GA12347@dhcp22.suse.cz> <20170612062918.GA4145@dhcp22.suse.cz> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 646 Lines: 13 On Mon, 12 Jun 2017, Michal Hocko wrote: > > These are not soft lockups, these are need_resched warnings. We monitor > > how long need_resched has been set and when a thread takes an excessive > > amount of time to reschedule after it has been set. A loop of 512 pages > > with ptl contention and doing {clear,copy}_user_highpage() shows that > > need_resched can sit without scheduling for an excessive amount of time. > > How much is excessive here? We monitor anything that holds the cpu for more than 1/20th of a second, but this specific occurrence has been observed for ~1/8th. The majority of mm/ is quite good in this regard.