Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B716FC433EF for ; Tue, 7 Dec 2021 16:27:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239643AbhLGQbC (ORCPT ); Tue, 7 Dec 2021 11:31:02 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:54594 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239631AbhLGQbA (ORCPT ); Tue, 7 Dec 2021 11:31:00 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 68F0C21763; Tue, 7 Dec 2021 16:27:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1638894449; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kIF7c/GC399ClUmX9kOCgFAXVwR1ENNV1ti6qlHDyxE=; b=MmhP3fHYP/OFuMvrgV6vV32tQ5r69cLHLQSZNcKJXiHI3PuOOZySlpPbdCBdk/fwjo3pi8 jgtjx5jIgAl9fwArKG26wB9uLnWJIB3iESXRxLkR53gZL+NHT3Fpf87hFG/XMfmrzJ0Ged AgL4ZRpRWaGRkCfSS+mWi64FVoAboUA= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 333D9A3B88; Tue, 7 Dec 2021 16:27:29 +0000 (UTC) Date: Tue, 7 Dec 2021 17:27:25 +0100 From: Michal Hocko To: David Hildenbrand Cc: Alexey Makhalov , Dennis Zhou , Eric Dumazet , "linux-mm@kvack.org" , Andrew Morton , Oscar Salvador , Tejun Heo , Christoph Lameter , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages Message-ID: References: <1043a1a4-b7f2-8730-d192-7cab9f15ee24@redhat.com> <77e785e6-cf34-0cff-26a5-852d3786a9b8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 07-12-21 17:09:50, David Hildenbrand wrote: > On 07.12.21 16:56, Michal Hocko wrote: > > On Tue 07-12-21 16:34:30, David Hildenbrand wrote: > >> On 07.12.21 16:29, Michal Hocko wrote: > >>> On Tue 07-12-21 16:09:39, David Hildenbrand wrote: > >>>> On 07.12.21 14:23, Michal Hocko wrote: > >>>>> On Tue 07-12-21 13:28:31, David Hildenbrand wrote: > >>>>> [...] > >>>>>> But maybe I am missing something important regarding online vs. offline > >>>>>> nodes that your patch changes? > >>>>> > >>>>> I am relying on alloc_node_data setting the node online. But if we are > >>>>> to change the call to arch_alloc_node_data then the patch needs to be > >>>>> more involved. Here is what I have right now. If this happens to be the > >>>>> right way then there is some additional work to sync up with the hotplug > >>>>> code. > >>>>> > >>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >>>>> index c5952749ad40..a296e934ad2f 100644 > >>>>> --- a/mm/page_alloc.c > >>>>> +++ b/mm/page_alloc.c > >>>>> @@ -8032,8 +8032,23 @@ void __init free_area_init(unsigned long *max_zone_pfn) > >>>>> /* Initialise every node */ > >>>>> mminit_verify_pageflags_layout(); > >>>>> setup_nr_node_ids(); > >>>>> - for_each_online_node(nid) { > >>>>> - pg_data_t *pgdat = NODE_DATA(nid); > >>>>> + for_each_node(nid) { > >>>>> + pg_data_t *pgdat; > >>>>> + > >>>>> + if (!node_online(nid)) { > >>>>> + pr_warn("Node %d uninitialized by the platform. Please report with memory map.\n", nid); > >>>>> + pgdat = arch_alloc_nodedata(nid); > >>>>> + pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat); > >>>>> + arch_refresh_nodedata(nid, pgdat); > >>>>> + node_set_online(nid); > >>>> > >>>> Setting all possible nodes online might result in quite some QE noice, > >>>> because all these nodes will then be visible in the sysfs and > >>>> try_offline_nodes() is essentially for the trash. > >>> > >>> I am not sure I follow. I believe sysfs will not get populate because I > >>> do not call register_one_node. > >> > >> arch/x86/kernel/topology.c:topology_init() > >> > >> for_each_online_node(i) > >> register_one_node(i); > > > > Right you are. > > > >>> You are right that try_offline_nodes will be reduce which is good imho. > >>> More changes will be possible (hopefully to drop some ugly code) on top > >>> of this change (or any other that achieves that there are no NULL pgdat > >>> for possible nodes). > >>> > >> > >> No to exposing actually offline nodes to user space via sysfs. > > > > Why is that a problem with the sysfs for non-populated nodes? > > > > https://lore.kernel.org/linuxppc-dev/20200428093836.27190-1-srikar@linux.vnet.ibm.com/t/ Thanks. It is good to be reminded that we are in cicling around this problem for quite some time without really forward much. > Contains some points -- certainly nothing unfixable but it clearly shows > that users expect only nodes with actual memory and cpus to be online -- > that's why we export the possible+online state to user space. My point > is to be careful with such drastic changes and do one step at a time. > > I think preallocation of the pgdat is a reasonable thing to have without > changing user-space visible semantics or even in-kernel semantics. So your proposal is to drop set_node_online from the patch and add it as a separate one which handles - sysfs part (i.e. do not register a node which doesn't span a physical address space) - hotplug side of (drop the pgd allocation, register node lazily when a first memblocks are registered) Makes sense? -- Michal Hocko SUSE Labs