From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id C4E136B0279 for ; Sun, 11 Jun 2017 19:28:13 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id a82so45933285pfc.8 for ; Sun, 11 Jun 2017 16:28:13 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id m132sor4010416pfc.31.2017.06.11.16.28.12 for (Google Transport Security); Sun, 11 Jun 2017 16:28:13 -0700 (PDT) Date: Sun, 11 Jun 2017 16:28:11 -0700 (PDT) From: David Rientjes Subject: Re: Sleeping BUG in khugepaged for i586 In-Reply-To: <20170610080941.GA12347@dhcp22.suse.cz> Message-ID: References: <20170605144401.5a7e62887b476f0732560fa0@linux-foundation.org> <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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Matthew Wilcox , Vlastimil Babka , Larry Finger , Andrew Morton , LKML , linux-mm@kvack.org On Sat, 10 Jun 2017, Michal Hocko wrote: > > > I would just pull the cond_resched out of __collapse_huge_page_copy > > > right after pte_unmap. But I am not really sure why this cond_resched is > > > really needed because the changelog of the patch which adds is is quite > > > terse on details. > > > > I'm not sure what could possibly be added to the changelog. We have > > encountered need_resched warnings during the iteration. > > Well, the part the changelog is not really clear about is whether the > HPAGE_PMD_NR loops itself is the source of the stall. This would be > quite surprising because doing 512 iterations taking up to 20+s sounds > way to much. I have no idea where you come up with 20+ seconds. 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. > So is it possible that we are missing a cond_resched > somewhere up the __collapse_huge_page_copy call path? No. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org