+ selftests-mm-add-folio-order-check-for-address-ranges.patch added to mm-new branch

+ selftests-mm-add-folio-order-check-for-address-ranges.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: add folio-order check for address ranges
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-add-folio-order-check-for-address-ranges.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-add-folio-order-check-for-address-ranges.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
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Subject: selftests/mm: add folio-order check for address ranges
Date: Tue, 8 Sep 2026 13:50:54 +0100

An mTHP collapse test needs to know that a range is backed by folios of
the target order, and that they sit where a collapse would put them. 
Nothing answers that today: is_backed_by_folio() classifies the folio
behind a single page, and check_huge_anon() reads smaps AnonHugePages,
which only accounts PMD mappings.

Add is_range_backed_by_order().  It requires every folio-sized, folio-
aligned part of the range to map one folio of that order, head to tail,
with the head at the start of the part.

A part backed by two smaller folios fails, and so does a folio mapped off
its natural alignment.  The mTHP cases need both to tell a collapsed range
from the one beside it.

Assisted-by: LLM
Link: https://lore.kernel.org/20260908125105.1510704-9-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/vm_util.c |   47 +++++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h |    2 +
 2 files changed, 49 insertions(+)

--- a/tools/testing/selftests/mm/vm_util.c~selftests-mm-add-folio-order-check-for-address-ranges
+++ a/tools/testing/selftests/mm/vm_util.c
@@ -552,6 +552,53 @@ fail:
 	return false;
 }
 
+/**
+ * is_range_backed_by_order() - check that a range is backed by @order folios
+ * @start: start of the range, a multiple of the folio size
+ * @len: length of the range in bytes, a multiple of the folio size
+ * @order: the folio order to check for
+ * @pagemap_fd: open /proc/<pid>/pagemap of the range's owner
+ * @kpageflags_fd: open /proc/kpageflags
+ *
+ * Every folio-sized, folio-aligned part of the range must map one folio of
+ * @order, head to tail, with the head at the start of the part.  A part
+ * backed by several smaller folios fails, and so does a folio mapped off
+ * its natural alignment.
+ *
+ * Returns: true if the whole range is backed that way, false otherwise.
+ */
+bool is_range_backed_by_order(char *start, size_t len, int order,
+			      int pagemap_fd, int kpageflags_fd)
+{
+	const unsigned long nr_pages = 1UL << order;
+	const size_t folio_size = nr_pages * psize();
+	char *vaddr;
+
+	if ((uintptr_t)start % folio_size || len % folio_size)
+		return false;
+
+	for (vaddr = start; vaddr < start + len; vaddr += folio_size) {
+		const unsigned long pfn = pagemap_get_pfn(pagemap_fd, vaddr);
+		unsigned long i;
+
+		/* Not present, or a tail page */
+		if (pfn == -1UL || pfn % nr_pages)
+			return false;
+
+		for (i = 1; i < nr_pages; i++) {
+			char *page = vaddr + i * psize();
+
+			if (pagemap_get_pfn(pagemap_fd, page) != pfn + i)
+				return false;
+		}
+
+		if (!is_backed_by_folio(vaddr, order, pagemap_fd, kpageflags_fd))
+			return false;
+	}
+
+	return true;
+}
+
 /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
 int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
 			      bool miss, bool wp, bool minor, uint64_t *ioctls)
--- a/tools/testing/selftests/mm/vm_util.h~selftests-mm-add-folio-order-check-for-address-ranges
+++ a/tools/testing/selftests/mm/vm_util.h
@@ -101,6 +101,8 @@ int gather_folio_orders(char *vaddr_star
 		int pagemap_fd, int kpageflags_fd, int orders[], int nr_orders);
 bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
 			int kpageflags_fd);
+bool is_range_backed_by_order(char *start, size_t len, int order,
+			      int pagemap_fd, int kpageflags_fd);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);
_

Patches currently in -mm which might be from kas@kernel.org are

mm-huge_memory-do-not-touch-frozen-folios-in-deferred_split_isolate.patch
mm-huge_memory-dequeue-the-deferred-split-after-the-split-freeze.patch
selftests-mm-raise-the-khugepaged-test-case-cap.patch
selftests-mm-skip-collapse_compound_extreme-where-the-pmd-is-too-large.patch
selftests-mm-scale-khugepageds-collapse-wait-with-the-pmd-size.patch
selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.patch
selftests-mm-make-the-swap-cases-swapout-reliable.patch
selftests-mm-stop-khugepaged-during-the-madv_collapse-cases.patch
selftests-mm-move-is_backed_by_folio-into-vm_util.patch
selftests-mm-add-folio-order-check-for-address-ranges.patch
selftests-mm-add-folio-order-detection-self-check.patch
selftests-mm-add-khugepaged-completion-barrier-helper.patch
selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch
selftests-mm-parameterize-the-mixed-source-collapse-case-by-source-order.patch
selftests-mm-cover-a-shared-source-collapse-write-race.patch
selftests-mm-run-every-supported-collapse-order-by-default.patch
selftests-mm-check-that-one-khugepaged-pass-collapses-one-window.patch
selftests-mm-add-khugepaged-race-harness.patch
selftests-mm-race-the-collapse-of-windows-with-holes.patch
selftests-mm-add-memory-pressure-threads-to-the-khugepaged-race-harness.patch
selftests-mm-zap-whole-pte-tables-in-the-khugepaged-race-harness.patch