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

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Message-ID: <78E39A43-D094-4706-B4BD-18C0B18EB2C3@vmware.com>
Date:   Tue, 7 Dec 2021 17:17:27 +0000
From:   Alexey Makhalov <amakhalov@...are.com>
To:     David Hildenbrand <david@...hat.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 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)  

Thanks,
—-Alexey