Re: [PATCH v4 0/6] Open HugeTLB allocation routine for more generic use

[Zi Yan]

+Qi

Since he is looking into adding memory reservation functionality to THP[1]
and this looks related.

[1] https://lore.kernel.org/all/cover.1782538002.git.zhengqi.arch@xxxxxxxxxxxxx/

On 2 Jul 2026, at 12:21, Ackerley Tng via B4 Relay wrote:

> Hi,
>
> The motivation for this patch series is guest_memfd, which would like
> to use HugeTLB as a generic source of huge pages but not adopt
> HugeTLB's reservation at mmap() time.
>
> By refactoring alloc_hugetlb_folio() and some dependent functions,
> there is now an option to allocate HugeTLB folios without providing a
> VMA. Specifically, HugeTLB allocation used to be dependent on the VMA
> to
>
> 1. Look up reservations in the resv_map
> 2. Get mpol, stored at vma->vm_policy
>
> This refactoring provides hugetlb_alloc_folio(), which focuses on just
> the allocation itself, and associated memory and HugeTLB charging
> (cgroups). alloc_hugetlb_folio() still handles reservations in the
> resv_map and subpools.
>
> Regarding naming, I'm definitely open to alternative names :) I chose
> hugetlb_alloc_folio() because I'm seeing this function as a general
> allocation function that is provided by the HugeTLB subsystem (hence
> the hugetlb_ prefix). I'm intending for alloc_hugetlb_folio() to be
> later refactored as a static function for use just by HugeTLB, and
> HugeTLBfs should probably use hugetlb_alloc_folio() directly.
>
> To see how hugetlb_alloc_folio() is used by guest_memfd, the most
> recent patch series that uses this more generic HugeTLB allocation
> routine is at [1], and a newer revision of that patch series is at
> [2].
>
> Independently of guest_memfd, I believe this change is useful in
> simplifying alloc_hugetlb_folio(). alloc_hugetlb_folio() was so
> coupled to a VMA that even HugeTLBfs allocates HugeTLB folios using a
> pseudo-VMA.
>
> Testing:
>
> + libhugetlbfs tests pass
> + ./tools/testing/selftests/mm/ksft_hugetlb.sh passes
>
> Andrew, thanks for nudging me to send a v4!
>
> Oscar, you mentioned that you wanted to do a closer review on v3, hope you
> find time to review v4 soon!
>
> Changes in this revision:
>
> + Define gfp within hugetlb_alloc_folio() instead of having it as a
>   parameter so users aren't able to override gfp arbitrarily as Oscar
>   requested.
> + Addressed some of Sashiko's comments [4]. Some of the issues I didn't address
>   were pre-existing issues. Since v3 of this series Sashiko was updated to
>   actually send mails. I'd let Sashiko point them out again and then we should
>   discuss those!
>
> [1] https://lore.kernel.org/all/cover.1747264138.git.ackerleytng@xxxxxxxxxx/T/
> [2] https://github.com/googleprodkernel/linux-cc/tree/wip-gmem-conversions-hugetlb-restructuring-12-08-25
> [3] https://lore.kernel.org/all/agqaUcVp_hwH-VXr@localhost.localdomain/
> [4] https://sashiko.dev/#/patchset/20260518-hugetlb-open-up-v3-0-e14b302477f8@xxxxxxxxxx
>
> RFC v1: https://lore.kernel.org/all/bb35a69a-5be9-45f5-a557-1902487a1bc2@xxxxxxxxx/
> v2: https://lore.kernel.org/r/20260506-hugetlb-open-up-v2-0-826a0c5f28fc@xxxxxxxxxx
> v3: https://lore.kernel.org/r/20260518-hugetlb-open-up-v3-0-e14b302477f8@xxxxxxxxxx
>
> ---
> Ackerley Tng (6):
>       mm: hugetlb: Consolidate interpretation of gbl_chg within alloc_hugetlb_folio()
>       mm: hugetlb: Move mpol interpretation out of alloc_buddy_hugetlb_folio_with_mpol()
>       mm: hugetlb: Move mpol interpretation out of dequeue_hugetlb_folio_vma()
>       mm: hugetlb: Use error variable in alloc_hugetlb_folio
>       mm: hugetlb: Move mem_cgroup_charge_hugetlb() earlier in allocation
>       mm: hugetlb: Refactor out hugetlb_alloc_folio()
>
>  include/linux/hugetlb.h        |  18 +++
>  include/uapi/linux/mempolicy.h |   2 +-
>  mm/hugetlb.c                   | 269 ++++++++++++++++++++++++-----------------
>  3 files changed, 175 insertions(+), 114 deletions(-)
> ---
> base-commit: 4a50a141f05a8d1737661b19ee22ff8455b94409
> change-id: 20260504-hugetlb-open-up-eaba80571b09
>
> Best regards,
> --
> Ackerley Tng <ackerleytng@xxxxxxxxxx>


Best Regards,
Yan, Zi