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

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Date:   Tue, 7 Dec 2021 19:03:28 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Alexey Makhalov <amakhalov@...are.com>
Cc:     Michal Hocko <mhocko@...e.com>, 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 18:17, Alexey Makhalov wrote:
> 
> 
>> On Dec 7, 2021, at 9:13 AM, David Hildenbrand <david@...hat.com> wrote:
>>
>> 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?
>>
> It is x86_64 VMware VM, not the regular one, but specially configured (1 vCPU per node,
> with hot-plug support, 128 possible nodes)  

I thought the pgdat would be smaller but I just gave it a test:

On my system, pgdata_t is 173824 bytes. So 128 nodes would correspond to
21 MiB, which is indeed a lot. I assume it's due to "struct zonelist",
which has MAX_ZONES_PER_ZONELIST == (MAX_NUMNODES * MAX_NR_ZONES) zone
references ...

-- 
Thanks,

David / dhildenb