linux-kernel - Re: [PATCH v6 03/10] mm,memory_hotplug: Implement numa node notifier

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Message-ID: <23431108-b5b8-4c8a-8869-8f994371e7a5@redhat.com>
Date: Mon, 16 Jun 2025 14:21:02 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Vlastimil Babka <vbabka@...e.cz>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Harry Yoo <harry.yoo@...cle.com>, Rakie Kim <rakie.kim@...com>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, Joshua Hahn <joshua.hahnjy@...il.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 03/10] mm,memory_hotplug: Implement numa node notifier

On 16.06.25 13:45, Oscar Salvador wrote:
> On Mon, Jun 16, 2025 at 10:52:31AM +0200, David Hildenbrand wrote:
>> Probably worth checking, to make sure we don't have accidental bugs in there
>> ...
> 
> I did a quick sweep, and we should be cool since users of the node notifier
> don't really use *_CANCEL* action. Only ADDED/REMOVED.
> 
> Now, users of memory notifier is a different story.
> E.g: page_ext will call offline_page_ext to mark the section->page_ext invalid.
> 
> online_page_ext does:
> 
>   base = alloc_page_ext(table_size, nid);
>   section->page_ext = (void *)base - page_ext_size * pfn;
> 
> This is fine, I think, offline_page_ext will not mark it as INVALID because
> section->page_ext is NULL, so we just skip it.
> 
> This is just one example. I checked some others like kasan and hyperv and they
> seem fine.
> And anyway, the we could already hit this situation with MEM_* notifiers, so
> nothing new.

Exactly. I recall I checked some of them in the past as well, when I 
stumbled over this behavior.

-- 
Cheers,

David / dhildenb