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

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Message-ID: <b6d472ba-e6cf-4c96-935d-88c842ab3cd8@redhat.com>
Date: Wed, 8 Oct 2025 21:01:09 +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 20:58, Gregory Price wrote:
> On Wed, Oct 08, 2025 at 04:44:22PM +0200, David Hildenbrand wrote:
>> On 08.10.25 16:18, Gregory Price wrote:
>>> On Wed, Oct 08, 2025 at 10:58:23AM +0200, David Hildenbrand wrote:
>>>> On 07.10.25 23:44, Gregory Price wrote:
>>>> I mean, this is as ugly as it gets.
>>>>
>>>> Can't we just let that old approach RIP where it belongs? :)
>>>>
>>>
>>> Definitely - just found this previously existed and wanted to probe for
>>> how offensive reintroducing it would be. Seems the answer is essentially
>>> "lets do it a little differently".
>>>
>>>> Something I could sympathize is is treaing gigantic pages that are actually
>>>> migratable as movable.
>>>>
>>> ...
>>>> -       gfp |= hugepage_movable_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
>>>> +       gfp |= hugepage_migration_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
>>>>
>>>> Assume you want to offline part of the ZONE_MOVABLE there might still be sufficient
>>>> space to possibly allocate a 1 GiB area elsewhere and actually move the gigantic page.
>>>>
>>>> IIRC, we do the same for memory offlining already.
>>>>
>>>
>>> This is generally true of other page sizes as well, though, isn't it?
>>> If the system is truly so pressured that it can't successfully move a
>>> 2MB page - offline may still fail.  So allowing 1GB pages is only a risk
>>> in the sense that they're harder to allocate new targets.
>>
>> Right, but memory defragmentation works on pageblock level, so 2 MiB is much
>> MUCH more reliable :)
>>
> 
> 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.

-- 
Cheers

David / dhildenb