linux-kernel - Re: [External] Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes

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Date:   Tue, 14 Feb 2023 20:09:40 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Teng Hu <huteng.ht@...edance.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <muchun.song@...ux.dev>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [External] Re: [PATCH] mm: page_alloc: don't allocate page from
 memoryless nodes



On 2023/2/14 19:58, David Hildenbrand wrote:
> On 14.02.23 12:48, David Hildenbrand wrote:
>> On 14.02.23 12:44, Mike Rapoport wrote:
>>> (added x86 folks)
>>>
>>> On Tue, Feb 14, 2023 at 12:29:42PM +0100, David Hildenbrand wrote:
>>>> On 14.02.23 12:26, Qi Zheng wrote:
>>>>> On 2023/2/14 19:22, David Hildenbrand wrote:
>>>>>>
>>>>>> TBH, this is the first time I hear of NODE_MIN_SIZE and it seems 
>>>>>> to be a
>>>>>> pretty x86 specific thing.
>>>>>>
>>>>>> Are we sure we want to get NODE_MIN_SIZE involved?
>>>>>
>>>>> Maybe add an arch_xxx() to handle it?
>>>>
>>>> I still haven't figured out what we want to achieve with 
>>>> NODE_MIN_SIZE at
>>>> all. It smells like an arch-specific hack looking at
>>>>
>>>> "Don't confuse VM with a node that doesn't have the minimum amount of
>>>> memory"
>>>>
>>>> Why shouldn't mm-core deal with that?
>>>
>>> Well, a node with <4M RAM is not very useful and bears all the 
>>> overhead of
>>> an extra live node.
>>
>> And totally not with 4.1M, haha.
>>
>> I really like the "Might fix boot" in the commit description.
>>
>>>
>>> But, hey, why won't we just drop that '< NODE_MIN_SIZE' and let 
>>> people with
>>> weird HW configurations just live with this?
>>
>>
>> ;)
>>
> 
> Actually, remembering 09f49dca570a ("mm: handle uninitialized numa nodes 
> gracefully"), this might be the right thing to do. That commit assumes 
> that all offline nodes would get the pgdat allocated in 
> free_area_init(). So that we end up with an allocated pgdat for all 
Can also See commit 1ca75fa7f19d ("arch/x86/mm/numa: Do not initialize 
nodes twice"). The commit message explains the initialization process
more clearly, it may be helpful. :)

> possible nodes. The reasoning IIRC was that we don't care about wasting 
> memory in weird VM setups.
> 
> CCing Michal.
> 

-- 
Thanks,
Qi