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>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 87c87f64bc05..817b8b4223fa 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_HUGETLB_H
 #define _LINUX_HUGETLB_H
 
+#include <linux/mempolicy.h>
 #include <linux/mm.h>
 #include <linux/mm_types.h>
 #include <linux/mmdebug.h>
@@ -682,6 +683,23 @@ struct hstate {
 int isolate_or_dissolve_huge_folio(struct folio *folio, struct list_head *list);
 int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn);
 void wait_for_freed_hugetlb_folios(void);
+
+struct mempolicy_interpreted {
+	int nid;
+	nodemask_t *nodemask;
+	enum mempolicy_mode mode;
+};
+
+enum hugetlb_alloc_flag {
+	HUGETLB_ALLOC_CHARGE_CGROUP_RSVD_BIT = 0,
+	HUGETLB_ALLOC_USE_GLOBAL_RESERVATIONS_BIT,
+};
+
+#define HUGETLB_ALLOC_CHARG_CGROUP_RSVD BIT(HUGETLB_ALLOC_CHARGE_CGROUP_RSVD_BIT)
+#define HUGETLB_ALLOC_USE_GLOBAL_RESERVATIONS BIT(HUGETLB_ALLOC_USE_GLOBAL_RESERVATIONS_BIT)
+
+struct folio *hugetlb_alloc_folio(struct hstate *h,
+		struct mempolicy_interpreted *mpoli, u8 alloc_flags);
 struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 				unsigned long addr, bool cow_from_owner);
 struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,