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=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 1C917C47E49 for ; Wed, 23 Oct 2019 16:41:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4A2121928 for ; Wed, 23 Oct 2019 16:41:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571848910; bh=MRBH1VATVsZvourRPVTgsvh4hpuCLiKSV8SkX4Ul+7A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=P58F/Vg68BBAMhDiMeiW1tMqC/o+8VcgT9grBPewK5z5Ow5zOv0OJjSXoMZ01Vwoh yNjPMJ73nu4vs+hmKyFHfcdlLU4lDL6608tBJn+D1zNt0opNyDayP2gGjjO6Aeim62 SKDFZpLu88VQn9f7l9LBFfj6mTYpnhMfgmWJGnrs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407326AbfJWQls (ORCPT ); Wed, 23 Oct 2019 12:41:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:54694 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730796AbfJWQls (ORCPT ); Wed, 23 Oct 2019 12:41:48 -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 9DA1EAC84; Wed, 23 Oct 2019 16:41:46 +0000 (UTC) Date: Wed, 23 Oct 2019 18:41:45 +0200 From: Michal Hocko To: Andrew Morton , Mel Gorman , Waiman Long Cc: 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: <20191023164145.GL17610@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: <20191023102737.32274-3-mhocko@kernel.org> 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 With a brown paper bag bug fixed. I have also added a note about low number of pages being more important as per Vlastimil's feedback >From 0282f604144a5c06fdf3cf0bb2df532411e7f8c9 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 23 Oct 2019 12:13:02 +0200 Subject: [PATCH] mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo 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 and low number of pages is much more interesting 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 Acked-by: Mel Gorman Signed-off-by: Michal Hocko --- mm/vmstat.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/mm/vmstat.c b/mm/vmstat.c index 4e885ecd44d1..c156ce24a322 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1383,12 +1383,29 @@ 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++; - seq_printf(m, "%6lu ", freecount); + list_for_each(curr, &area->free_list[mtype]) { + /* + * 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) { + overflow = true; + spin_unlock_irq(&zone->lock); + cond_resched(); + spin_lock_irq(&zone->lock); + break; + } + } + seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount); } seq_putc(m, '\n'); } -- 2.20.1 -- Michal Hocko SUSE Labs