Message-ID: <27da47d9-2daf-c580-66e2-cae55f53e784@bytedance.com>
Date:   Tue, 14 Feb 2023 20:09:40 +0800
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Subject: Re: [External] Re: [PATCH] mm: page_alloc: don't allocate page from
 memoryless nodes
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To:     David Hildenbrand <david@redhat.com>,
        Mike Rapoport <rppt@kernel.org>
Cc:     Vlastimil Babka <vbabka@suse.cz>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Teng Hu <huteng.ht@bytedance.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Oscar Salvador <osalvador@suse.de>,
        Muchun Song <muchun.song@linux.dev>,
        Michal Hocko <mhocko@kernel.org>
References: <20230212110305.93670-1-zhengqi.arch@bytedance.com>
 <2484666e-e78e-549d-e075-b2c39d460d71@suse.cz>
 <85af4ada-96c8-1f99-90fa-9b6d63d0016e@bytedance.com>
 <c6908bd0-5f76-47eb-2b77-ce8f7bf9fbff@suse.cz>
 <eefc40e5-a14b-22c5-3480-6786afa1c8f4@redhat.com>
 <Y+tXrK/g1Nrd/q1h@kernel.org>
 <67240e55-af49-f20a-2b4b-b7d574cd910d@gmail.com>
 <22f0e262-982e-ea80-e52a-a3c924b31d58@redhat.com>
 <dbfbd982-27f3-0d72-49e0-d3dd5fe636a8@bytedance.com>
 <4386151c-0328-d207-9a71-933ef61817f9@redhat.com>
 <Y+t0Bhu7BCzH2Dp4@kernel.org>
 <a7f8be91-32c1-bfbe-7e81-5b1e818ba01d@redhat.com>
 <a09bfe3a-87e4-f8ce-89bb-c5fde8cc33c9@redhat.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
In-Reply-To: <a09bfe3a-87e4-f8ce-89bb-c5fde8cc33c9@redhat.com>
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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