linux-kernel - Re: [PATCH 2/2] mm: keep nid around during hot-remove

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Message-ID: <e780e9af-e23d-44ff-ae0f-a8f4ee098a1c@redhat.com>
Date: Wed, 7 Aug 2024 13:50:00 +0200
From: David Hildenbrand <david@...hat.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>, agordeev@...ux.ibm.com,
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Subject: Re: [PATCH 2/2] mm: keep nid around during hot-remove

On 07.08.24 13:32, David Hildenbrand wrote:
> On 07.08.24 00:14, Pasha Tatashin wrote:
>> nid is needed during memory hot-remove in order to account the
>> information about the memmap overhead that is being removed.
>>
>> In addition, we cannot use page_pgdat(pfn_to_page(pfn)) during
>> hotremove after remove_pfn_range_from_zone().
>>
>> We also cannot determine nid from walking through memblocks after
>> remove_memory_block_devices() is called.
>>
>> Therefore, pass nid down from the beginning of hotremove to where
>> it is used for the accounting purposes.
> 
> I was happy to finally remove that nid parameter for good in:
> 
> commit 65a2aa5f482ed0c1b5afb9e6b0b9e0b16bb8b616
> Author: David Hildenbrand <david@...hat.com>
> Date:   Tue Sep 7 19:55:04 2021 -0700
> 
>       mm/memory_hotplug: remove nid parameter from arch_remove_memory()
> 
> To ask the real question: Do we really need this counter per-nid at all?
> 
> Seems to over-complicate things.

Case in point: I think the handling is wrong?

Just because some memory belongs to a nid doesn't mean that the vmemmap 
was allocated from that nid?

Wouldn't we want to look at the actual nid the vmemmap page belongs to 
that we are removing?

-- 
Cheers,

David / dhildenb