Re: [PATCH 6/6] mm: rename ARCH_ENABLE_THP_MIGRATION to ARCH_SUPPORTS_PMD_SOFTLEAF

[Zi Yan]

On 1 Jul 2026, at 16:50, David Hildenbrand (Arm) wrote:

> On 7/1/26 22:39, Zi Yan wrote:
>> On 1 Jul 2026, at 16:03, David Hildenbrand (Arm) wrote:
>>
>>> On 6/30/26 18:34, Usama Arif wrote:
>>>> CONFIG_ARCH_ENABLE_THP_MIGRATION started life gating just PMD-level
>>>> migration entries, but has grown to gate the entire PMD-level softleaf
>>>> machinery: migration entries, device-private entries, and soon swap
>>>> entries.
>>>
>>> device-private really relies on migration support.
>>>
>>> See do_huge_pmd_device_private() where we migrate back to CPU memory.
>>>
>>> The whole concept is pased on migration. So that's why it currently makes sense.
>>>
>>> So "has grown to" is not quite accurate. It's a different story with swap
>>> entries (that can exist even without migration support).
>>>
>>>
>>>> Rename CONFIG_ARCH_ENABLE_THP_MIGRATION to CONFIG_ARCH_SUPPORTS_PMD
>>>> _SOFTLEAF to make this clear.  This is a pure rename: the set of
>>>> selecting architectures (x86, arm64, s390, riscv, loongarch, and
>>>> powerpc on PPC_BOOK3S_64) and the gating semantics are unchanged.
>>>
>>> Hm, that makes me wonder what it would take to make this all just be implicitly
>>> supported by CONFIG_TRANSPARENT_HUGEPAGE.
>>>
>>> Looks like someone would have the courage to touch stuff like arc, mips and
>>> sparc64 (+arm and x86, but that's less of a concern :) ).
>>
>> You mean me back in 2018[1]? ;)
>>
>> At least I got a no go for s390.
>
> hah! and 8 years later it seems to exist upstream :)
>
> commit 10dd5a0009898ba35eafeb6087e5c83b84742ff1
> Author: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> Date:   Tue Jul 29 13:16:19 2025 +0200
>
>     s390/mm: Enable THP_SWAP and THP_MIGRATION
>
>     After hugetlbfs PTE_MARKER support for s390 introduced region-third and
>     segment table swap entries, it is now possible to also enable THP_SWAP
>     and THP_MIGRATION for s390.
>
> So, with that out of the way, could you revive your patchset?
>
Sure. Will put that on my TODO list.

Best Regards,
Yan, Zi