From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61DE7CA9EB6 for ; Wed, 23 Oct 2019 13:37:26 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 12DAD20640 for ; Wed, 23 Oct 2019 13:37:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 12DAD20640 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 725256B0003; Wed, 23 Oct 2019 09:37:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6D6976B0006; Wed, 23 Oct 2019 09:37:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5EBEB6B0007; Wed, 23 Oct 2019 09:37:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0180.hostedemail.com [216.40.44.180]) by kanga.kvack.org (Postfix) with ESMTP id 3DBB66B0003 for ; Wed, 23 Oct 2019 09:37:25 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id E5F4145D8 for ; Wed, 23 Oct 2019 13:37:24 +0000 (UTC) X-FDA: 76075151208.30.team47_7adff68bbf061 X-HE-Tag: team47_7adff68bbf061 X-Filterd-Recvd-Size: 4407 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Wed, 23 Oct 2019 13:37:24 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 84699B59E; Wed, 23 Oct 2019 13:37:22 +0000 (UTC) Date: Wed, 23 Oct 2019 15:37:20 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Andrew Morton , Mel Gorman , Waiman Long , Johannes Weiner , Roman Gushchin , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini , linux-mm@kvack.org, LKML Subject: Re: [RFC PATCH 2/2] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo Message-ID: <20191023133720.GA17610@dhcp22.suse.cz> References: <20191023095607.GE3016@techsingularity.net> <20191023102737.32274-1-mhocko@kernel.org> <20191023102737.32274-3-mhocko@kernel.org> <30211965-8ad0-416d-0fe1-113270bd1ea8@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <30211965-8ad0-416d-0fe1-113270bd1ea8@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 23-10-19 15:32:05, Vlastimil Babka wrote: > On 10/23/19 12:27 PM, Michal Hocko wrote: > > From: Michal Hocko > > > > pagetypeinfo_showfree_print is called by zone->lock held in irq mode. > > This is not really nice because it blocks both any interrupts on that > > cpu and the page allocator. On large machines this might even trigger > > the hard lockup detector. > > > > Considering the pagetypeinfo is a debugging tool we do not really need > > exact numbers here. The primary reason to look at the outuput is to see > > how pageblocks are spread among different migratetypes therefore putting > > a bound on the number of pages on the free_list sounds like a reasonable > > tradeoff. > > > > The new output will simply tell > > [...] > > Node 6, zone Normal, type Movable >100000 >100000 >100000 >100000 41019 31560 23996 10054 3229 983 648 > > > > instead of > > Node 6, zone Normal, type Movable 399568 294127 221558 102119 41019 31560 23996 10054 3229 983 648 > > > > The limit has been chosen arbitrary and it is a subject of a future > > change should there be a need for that. > > > > Suggested-by: Andrew Morton > > Signed-off-by: Michal Hocko > > Hmm dunno, I would rather e.g. hide the file behind some config or boot > option than do this. Or move it to /sys/kernel/debug ? But those wouldn't really help to prevent from the lockup, right? Besides that who would enable that config and how much of a difference would root only vs. debugfs make? Is the incomplete value a real problem? > > --- > > mm/vmstat.c | 19 ++++++++++++++++++- > > 1 file changed, 18 insertions(+), 1 deletion(-) > > > > diff --git a/mm/vmstat.c b/mm/vmstat.c > > index 4e885ecd44d1..762034fc3b83 100644 > > --- a/mm/vmstat.c > > +++ b/mm/vmstat.c > > @@ -1386,8 +1386,25 @@ static void pagetypeinfo_showfree_print(struct seq_file *m, > > > > area = &(zone->free_area[order]); > > > > - list_for_each(curr, &area->free_list[mtype]) > > + list_for_each(curr, &area->free_list[mtype]) { > > freecount++; > > + /* > > + * Cap the free_list iteration because it might > > + * be really large and we are under a spinlock > > + * so a long time spent here could trigger a > > + * hard lockup detector. Anyway this is a > > + * debugging tool so knowing there is a handful > > + * of pages in this order should be more than > > + * sufficient > > + */ > > + if (freecount > 100000) { > > + seq_printf(m, ">%6lu ", freecount); > > + spin_unlock_irq(&zone->lock); > > + cond_resched(); > > + spin_lock_irq(&zone->lock); > > + continue; > > + } > > + } > > seq_printf(m, "%6lu ", freecount); > > } > > seq_putc(m, '\n'); > > -- Michal Hocko SUSE Labs