+ mm-memfd-reserve-hugetlb-folios-before-allocation.patch added to mm-new branch

+ mm-memfd-reserve-hugetlb-folios-before-allocation.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/memfd: reserve hugetlb folios before allocation
has been added to the -mm mm-new branch.  Its filename is
     mm-memfd-reserve-hugetlb-folios-before-allocation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memfd-reserve-hugetlb-folios-before-allocation.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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fixup patches in mm-new.

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------------------------------------------------------
From: Vivek Kasireddy <vivek.kasireddy@intel.com>
Subject: mm/memfd: reserve hugetlb folios before allocation
Date: Tue, 17 Jun 2025 22:30:54 -0700

When we try to allocate a folio via alloc_hugetlb_folio_reserve(), we need
to ensure that there is an active reservation associated with the
allocation.  Otherwise, our allocation request would fail if there are no
active reservations made at that moment against any other allocations. 
This is because alloc_hugetlb_folio_reserve() checks h->resv_huge_pages
before proceeding with the allocation.

Therefore, to address this issue, we just need to make a reservation (by
calling hugetlb_reserve_pages()) before we try to allocate the folio. 
This will also ensure that proper region/subpool accounting is done
associated with our allocation.

Link: https://lkml.kernel.org/r/20250618053415.1036185-3-vivek.kasireddy@intel.com
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Cc: Steve Sistare <steven.sistare@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/hugetlb.h |    5 +++++
 mm/hugetlb.c            |    5 -----
 mm/memfd.c              |   17 ++++++++++++++---
 3 files changed, 19 insertions(+), 8 deletions(-)

--- a/include/linux/hugetlb.h~mm-memfd-reserve-hugetlb-folios-before-allocation
+++ a/include/linux/hugetlb.h
@@ -740,6 +740,11 @@ extern unsigned int default_hstate_idx;
 
 #define default_hstate (hstates[default_hstate_idx])
 
+static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
+{
+	return HUGETLBFS_SB(inode->i_sb)->spool;
+}
+
 static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio)
 {
 	return folio->_hugetlb_subpool;
--- a/mm/hugetlb.c~mm-memfd-reserve-hugetlb-folios-before-allocation
+++ a/mm/hugetlb.c
@@ -284,11 +284,6 @@ static long hugepage_subpool_put_pages(s
 	return ret;
 }
 
-static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
-{
-	return HUGETLBFS_SB(inode->i_sb)->spool;
-}
-
 static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
 {
 	return subpool_inode(file_inode(vma->vm_file));
--- a/mm/memfd.c~mm-memfd-reserve-hugetlb-folios-before-allocation
+++ a/mm/memfd.c
@@ -70,7 +70,6 @@ struct folio *memfd_alloc_folio(struct f
 #ifdef CONFIG_HUGETLB_PAGE
 	struct folio *folio;
 	gfp_t gfp_mask;
-	int err;
 
 	if (is_file_hugepages(memfd)) {
 		/*
@@ -79,12 +78,19 @@ struct folio *memfd_alloc_folio(struct f
 		 * alloc from. Also, the folio will be pinned for an indefinite
 		 * amount of time, so it is not expected to be migrated away.
 		 */
+		struct inode *inode = file_inode(memfd);
 		struct hstate *h = hstate_file(memfd);
+		int err = -ENOMEM;
+		long nr_resv;
 
 		gfp_mask = htlb_alloc_mask(h);
 		gfp_mask &= ~(__GFP_HIGHMEM | __GFP_MOVABLE);
 		idx >>= huge_page_order(h);
 
+		nr_resv = hugetlb_reserve_pages(inode, idx, idx + 1, NULL, 0);
+		if (nr_resv < 0)
+			return ERR_PTR(nr_resv);
+
 		folio = alloc_hugetlb_folio_reserve(h,
 						    numa_node_id(),
 						    NULL,
@@ -95,12 +101,17 @@ struct folio *memfd_alloc_folio(struct f
 							idx);
 			if (err) {
 				folio_put(folio);
-				return ERR_PTR(err);
+				goto err_unresv;
 			}
+
+			hugetlb_set_folio_subpool(folio, subpool_inode(inode));
 			folio_unlock(folio);
 			return folio;
 		}
-		return ERR_PTR(-ENOMEM);
+err_unresv:
+		if (nr_resv > 0)
+			hugetlb_unreserve_pages(inode, idx, idx + 1, 0);
+		return ERR_PTR(err);
 	}
 #endif
 	return shmem_read_folio(memfd->f_mapping, idx);
_

Patches currently in -mm which might be from vivek.kasireddy@intel.com are

mm-hugetlb-make-hugetlb_reserve_pages-return-nr-of-entries-updated.patch
mm-memfd-reserve-hugetlb-folios-before-allocation.patch
selftests-udmabuf-add-a-test-to-pin-first-before-writing-to-memfd.patch