linux-kernel - Re: [PATCH v3] mm: fix panic in __alloc

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Date:   Tue, 7 Dec 2021 18:13:55 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Alexey Makhalov <amakhalov@...are.com>,
        Michal Hocko <mhocko@...e.com>
Cc:     Dennis Zhou <dennis@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages

On 07.12.21 18:02, Alexey Makhalov wrote:
> 
> 
>> On Dec 7, 2021, at 8:36 AM, Michal Hocko <mhocko@...e.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?


-- 
Thanks,

David / dhildenb