Re: [PATCH 2/4] mm: not __SetPageReserved on initializing hot-plugged memory

Wei Yang
2024-06-29T08:32:28Z

On Sat, Jun 29, 2024 at 08:19:49AM +0200, David Hildenbrand wrote:
>On 29.06.24 03:33, Wei Yang wrote:
>> Initialize all pages reserved is an ancient behavior.
>>
>> Since commit 92923ca3aace ("mm: meminit: only set page reserved in the
>> memblock region"), SetPageReserved is removed from
>> __init_single_page(). Only those reserved pages are marked PG_reserved.
>>
>> But we still set PG_reserved on offline and check it on online.
>>
>> Following two commits removed both of them:
>>
>> * Commit 0ee5f4f31d36 ("mm/page_alloc.c: don't set pages PageReserved()
>> when offlining") removed the set on offline.
>> * Commit 5ecae6359e3a ("mm/memory_hotplug: drop PageReserved() check in
>> online_pages_range()") removed the check on online.
>>
>> This means we set PG_reserved for hot-plugged memory at initialization
>> is not helpful and a little different from bootmem initialization path.
>> Now we can remove it.
>
>It's not that easy for ZONE_DEVICE.
>
>Also, see mm/mm-stable
>
>commit 3dadec1babf9eee0c67c967df931d6f0cb124a04
>Author: David Hildenbrand <david@redhat.com>
>Date: Fri Jun 7 11:09:36 2024 +0200
>
> mm: pass meminit_context to __free_pages_core()
>
> Patch series "mm/memory_hotplug: use PageOffline() instead of
> PageReserved() for !ZONE_DEVICE".
>
>
>commit b873faaa609ab44c223b2327f55d2b6a2ba4ca9c
>Author: David Hildenbrand <david@redhat.com>
>Date: Fri Jun 7 11:09:37 2024 +0200
>
> mm/memory_hotplug: initialize memmap of !ZONE_DEVICE with PageOffline()
>instead of PageReserved()
>

Let me try to understand this.

You also tries to get rid of PG_reserved but you want PG_offline instead,
because this benefit virtio-mem, right?

But I don't get why PG_offline is wrong for ZONE_DEVICE. I may miss some
knowledge for it.

>
>If you want to work on removing it for ZONE_DEVICE, one idea
>is to replace all relevant PageReserved() checks by a
>more generic function that would check PageReserved() and the zone
>
>
>--
>Cheers,
>
>David / dhildenb

--
Wei Yang
Help you, Help me