Date:   Wed, 8 Dec 2021 09:04:21 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Alexey Makhalov <amakhalov@vmware.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Dennis Zhou <dennis@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages
Message-ID: <YbBnBQLcOSJaB7Px@dhcp22.suse.cz>
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On Tue 07-12-21 17:17:27, Alexey Makhalov wrote:
> 
> 
> > On Dec 7, 2021, at 9:13 AM, David Hildenbrand <david@redhat.com> wrote:
> > 
> > On 07.12.21 18:02, Alexey Makhalov wrote:
> >> 
> >> 
> >>> On Dec 7, 2021, at 8:36 AM, Michal Hocko <mhocko@suse.com> wrote:
> >>> 
> >>> On Tue 07-12-21 17:27:29, Michal Hocko wrote:
> >>> [...]
> >>>> 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)
> >>> 
> >>> In other words, the first stage
> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >>> index c5952749ad40..f9024ba09c53 100644
> >>> --- a/mm/page_alloc.c
> >>> +++ b/mm/page_alloc.c
> >>> @@ -6382,7 +6382,11 @@ static void __build_all_zonelists(void *data)
> >>> 	if (self && !node_online(self->node_id)) {
> >>> 		build_zonelists(self);
> >>> 	} else {
> >>> -		for_each_online_node(nid) {
> >>> +		/*
> >>> +		 * All possible nodes have pgdat preallocated
> >>> +		 * free_area_init
> >>> +		 */
> >>> +		for_each_node(nid) {
> >>> 			pg_data_t *pgdat = NODE_DATA(nid);
> >>> 
> >>> 			build_zonelists(pgdat);
> >> 
> >> Will it blow up memory usage for the nodes which might never be onlined?
> >> I prefer the idea of init on demand.
> >> 
> >> Even now there is an existing problem.
> >> In my experiments, I observed _huge_ memory consumption increase by increasing number
> >> of possible numa nodes. I’m going to report it in separate mail thread.
> > 
> > I already raised that PPC might be problematic in that regard. Which
> > architecture / setup do you have in mind that can have a lot of possible
> > nodes?
> > 
> It is x86_64 VMware VM, not the regular one, but specially configured (1 vCPU per node,
> with hot-plug support, 128 possible nodes)  

This is slightly tangent but could you elaborate more on this setup and
reasoning behind it. I was already curious when you mentioned this
previously. Why would you want to have so many nodes and having 1:1 with
CPUs. What is the resulting NUMA topology?
-- 
Michal Hocko
SUSE Labs