[RFC PATCH v1 0/7] Open HugeTLB allocation routine for more generic use

[Ackerley Tng]

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.

I would like to get feedback on:

1. Opening up HugeTLB's allocation for more generic use
2. Reverting and re-adopting the try-commit-cancel protocol for memory
   charging

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.

[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

Ackerley Tng (7):
  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()
  Revert "memcg/hugetlb: remove memcg hugetlb try-commit-cancel
    protocol"
  mm: hugetlb: Adopt memcg try-commit-cancel protocol
  mm: memcontrol: Remove now-unused function mem_cgroup_charge_hugetlb
  mm: hugetlb: Refactor out hugetlb_alloc_folio()

 include/linux/hugetlb.h    |  11 ++
 include/linux/memcontrol.h |  21 +++-
 mm/hugetlb.c               | 228 +++++++++++++++++++++----------------
 mm/memcontrol.c            |  77 ++++++++-----
 4 files changed, 212 insertions(+), 125 deletions(-)


base-commit: db9571a66156bfbc0273e66e5c77923869bda547
--
2.53.0.310.g728cabbaf7-goog