linux-kernel - Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as

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Message-ID: <1763f0d9-37fc-4c3e-b31b-2cfac33d5c95@redhat.com>
Date: Wed, 8 Oct 2025 21:52:09 +0200
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>
Cc: linux-mm@...ck.org, corbet@....net, muchun.song@...ux.dev,
 osalvador@...e.de, akpm@...ux-foundation.org, hannes@...xchg.org,
 laoar.shao@...il.com, brauner@...nel.org, mclapinski@...gle.com,
 joel.granados@...nel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
 Michal Hocko <mhocko@...e.com>,
 Alexandru Moise <00moses.alexander00@...il.com>,
 David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable
 sysctl"

On 08.10.25 21:44, Gregory Price wrote:
> On Wed, Oct 08, 2025 at 09:01:09PM +0200, David Hildenbrand wrote:
>>>
>>> fwiw this works cleanly.  Just dropping this here, but should continue
>>> the zone conversation.  I need to check, but does this actually allow
>>> pinnable allocations?  I thought pinning kicked off migration.
>>
>> Yes, it should because longterm pinning -> unmovable.
>>
> 
> You know i just realized, my test here only works before I allocated 1GB
> pages on both node0 and node1.  If I only allocate 1gb hugetlb on node1,
> then the migrate pages call fails - because there are no 1gb pages
> available there.
> 
> I imagine this would cause hot-unplug/offline to fail since it uses the
> same migration mechanisms.
> 
> Worse I would imagine this would fail for 2MB.
> 
> Seems like the 1GB limitation is arbitrary if 2MB causes the same issue.

Yeah, with hugetlb allocations there are no guarantees either. It's just 
that page compaction / defragmentation makes it much less likely to fail 
in many scenarios.

-- 
Cheers

David / dhildenb