mm: hugetlb: refactor out hugetlb_alloc_folio()

Refactor out hugetlb_alloc_folio() from alloc_hugetlb_folio(), which
handles allocation of a folio and memory and HugeTLB charging to cgroups.

This refactoring decouples the HugeTLB page allocation from VMAs,
specifically:

1. Reservations (as in resv_map) are stored in the vma
2. mpol is stored at vma->vm_policy
3. A vma must be used for allocation even if the pages are not meant to be
   used by host process.

Without this coupling, VMAs are no longer a requirement for allocation. 
This opens up the allocation routine for usage without VMAs, which will
allow guest_memfd to use HugeTLB as a more generic allocator of huge
pages, since guest_memfd memory may not have any associated VMAs by
design.  In addition, direct allocations from HugeTLB could possibly be
refactored to avoid the use of a pseudo-VMA.

Also, this decouples HugeTLB page allocation from HugeTLBfs, where the
subpool is stored at the fs mount.  This is also a requirement for
guest_memfd, where the plan is to have a subpool created per-fd and stored
on the inode.

Provide and use alloc_flags to allow more allocation knobs in future
without expanding the number of parameters in hugetlb_alloc_folio().

No functional change intended.

Link: https://lore.kernel.org/20260702-hugetlb-open-up-v4-6-d53cefcccf34@google.com
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Shivank Garg <shivankg@amd.com>
Cc: Vishal Annapurve <vannapurve@google.com>
Cc: Yan Zhao <yan.y.zhao@intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions