Re: [PATCH] Revert "mm, hugetlb: remove hugepages_treat_as_movable sysctl"

David Hildenbrand
2025-10-08T15:14:32Z

On 08.10.25 16:59, Michal Hocko wrote:
> On Wed 08-10-25 10:58:23, David Hildenbrand wrote:
>> On 07.10.25 23:44, Gregory Price wrote:
> [...]
>>> @@ -926,7 +927,8 @@ static inline gfp_t htlb_alloc_mask(struct hstate *h)
>>> {
>>> gfp_t gfp = __GFP_COMP | __GFP_NOWARN;
>>> - gfp |= hugepage_movable_supported(h) ? GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
>>> + gfp |= (hugepage_movable_supported(h) || hugepages_treat_as_movable) ?
>>> + GFP_HIGHUSER_MOVABLE : GFP_HIGHUSER;
>>
>> I mean, this is as ugly as it gets.
>>
>> Can't we just let that old approach RIP where it belongs? :)
>>
>> If something unmovable, it does not belong on ZONE_MOVABLE, as simple as that.
>
> yes, I do agree. This is just muddying the semantic of the zone.
>
> Maybe what we really want is to have a configurable zone rather than a
> very specific consumer of it instead. What do I mean by that? We clearly
> have physically (DMA, DMA32) and usability (NORMAL, MOVABLE) constrained
> zones. So rather than having a MOVABLE zone we can have a single zone
> $FOO_NAME zone with configurable attributes - like allocation
> constrains (kernel, user, movable, etc). Now that we can overlap zones
> this should allow for quite a lot flexibility. Implementation wise this
> would require some tricks as we have 2 zone types for potentially 3
> different major usecases (kernel allocations, userspace reserved ranges
> without movability and movable allocations). I haven't thought this
> through completely and mostly throwing this as an idea (maybe won't
> work). Does that make sense?

I suggested something called PREFER_MOVABLE in the past, that would
prefer movable allocations but nothing would stop unmovable allocations
to end up on it. But only as a last resort or when explicitly requested
(e.g., gigantic pages).

Maybe that's similar to what you have in mind?

--
Cheers

David / dhildenb