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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 333F1C47E49 for ; Wed, 23 Oct 2019 16:10:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 07008205C9 for ; Wed, 23 Oct 2019 16:10:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571847035; bh=ueMGX3zUjSmWxI3rEGuXDUt3LEls0hEweJa1cUzWht4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ZVXmabWbD/EQtSeIrbnygT1px6bghcdfqnYvjBUGeEj6choxr3YYTCL2L27HeJOdx DBpBy5PilS018SReP05WtZlqiDTtDDlaDd/OXsoYauqLpIZiyHfiHbWiWdWnEeYoIZ ccby0UmuPx1GjAoNMe1c8tbLT4I2UaxtIh+rxJDk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407058AbfJWQKe (ORCPT ); Wed, 23 Oct 2019 12:10:34 -0400 Received: from mx2.suse.de ([195.135.220.15]:37366 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2404582AbfJWQKd (ORCPT ); Wed, 23 Oct 2019 12:10:33 -0400 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 0F75BB1C1; Wed, 23 Oct 2019 16:10:31 +0000 (UTC) Date: Wed, 23 Oct 2019 18:10:29 +0200 From: Michal Hocko To: Waiman Long Cc: Andrew Morton , Mel Gorman , Johannes Weiner , Roman Gushchin , Vlastimil Babka , 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: <20191023161029.GK17610@dhcp22.suse.cz> References: <20191023095607.GE3016@techsingularity.net> <20191023102737.32274-1-mhocko@kernel.org> <20191023102737.32274-3-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 23-10-19 10:56:30, Waiman Long wrote: > On 10/23/19 6:27 AM, 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 > > --- > > 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; > list_for_each() is a for loop. The continue statement will just iterate > the rests with the possibility that curr will be stale. Should we use > goto to jump after the seq_print() below? You are right. Kinda brown paper back material. Sorry about that. What about this on top? --- diff --git a/mm/vmstat.c b/mm/vmstat.c index 762034fc3b83..c156ce24a322 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1383,11 +1383,11 @@ static void pagetypeinfo_showfree_print(struct seq_file *m, unsigned long freecount = 0; struct free_area *area; struct list_head *curr; + bool overflow = false; area = &(zone->free_area[order]); 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 @@ -1397,15 +1397,15 @@ static void pagetypeinfo_showfree_print(struct seq_file *m, * of pages in this order should be more than * sufficient */ - if (freecount > 100000) { - seq_printf(m, ">%6lu ", freecount); + if (++freecount >= 100000) { + overflow = true; spin_unlock_irq(&zone->lock); cond_resched(); spin_lock_irq(&zone->lock); - continue; + break; } } - seq_printf(m, "%6lu ", freecount); + seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount); } seq_putc(m, '\n'); } -- Michal Hocko SUSE Labs