From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id E2ACA6B0292 for ; Sat, 10 Jun 2017 04:09:46 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id g76so12191392wrd.3 for ; Sat, 10 Jun 2017 01:09:46 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j22si3385337wre.322.2017.06.10.01.09.45 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sat, 10 Jun 2017 01:09:45 -0700 (PDT) Date: Sat, 10 Jun 2017 10:09:42 +0200 From: Michal Hocko Subject: Re: Sleeping BUG in khugepaged for i586 Message-ID: <20170610080941.GA12347@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Matthew Wilcox , Vlastimil Babka , Larry Finger , Andrew Morton , LKML , linux-mm@kvack.org On Fri 09-06-17 15:38:44, David Rientjes wrote: > On Thu, 8 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. So is it possible that we are missing a cond_resched somewhere up the __collapse_huge_page_copy call path? Or do we really do something stupidly expensive here? > We fix these > because need_resched warnings suppress future warnings of the same type > for issues that are more important. Sure thing. I do care about soft lockups as well. > I can fix the i386 issue but removing the cond_resched() entirely isn't > really suitable. I am not calling for a complete removal. I just do not yet see what is the source of the long processing of the the loop. -- Michal Hocko SUSE Labs -- 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