+ selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.patch added to mm-new branch

+ selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: skip khugepaged page cache cases without a PMD folio
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.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: skip khugepaged page cache cases without a PMD folio
Date: Tue, 8 Sep 2026 13:50:50 +0100

The page cache caps folio order at MAX_PAGECACHE_ORDER, which is below the
PMD order on arm64 with 64K pages, where a PMD is 512M.  A PMD-sized page
cache folio is impossible there, so the kernel refuses these collapses:
MADV_COLLAPSE answers -EINVAL and khugepaged passes over the range.  Four
shmem cases ask for a PMD-sized folio anyway, fail, and the run bails out
in the middle.

Skip the shmem and file mem types where the cap is below the PMD order.

The cap is not shmem-specific: it applies to every file folio.  Add
thp_file_supported_orders() to read the orders the page cache allows.

Anonymous collapse is unaffected: its orders are not capped this way.

Assisted-by: LLM
Link: https://lore.kernel.org/20260908125105.1510704-5-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/lib/mm/hugepage_settings.h        |    9 +++++++++
 tools/testing/selftests/mm/khugepaged.c |   19 +++++++++++++++++++
 2 files changed, 28 insertions(+)

--- a/tools/lib/mm/hugepage_settings.h~selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio
+++ a/tools/lib/mm/hugepage_settings.h
@@ -87,6 +87,15 @@ void thp_set_read_ahead_path(char *path)
 unsigned long thp_supported_orders(void);
 unsigned long thp_shmem_supported_orders(void);
 
+/*
+ * The per-order shmem_enabled attribute is created for the orders the page
+ * cache can hold, not just for shmem, so it answers for regular files too.
+ */
+static inline unsigned long thp_file_supported_orders(void)
+{
+	return thp_shmem_supported_orders();
+}
+
 bool thp_available(void);
 bool thp_is_enabled(void);
 
--- a/tools/testing/selftests/mm/khugepaged.c~selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio
+++ a/tools/testing/selftests/mm/khugepaged.c
@@ -1358,6 +1358,25 @@ int main(int argc, char **argv)
 
 	setbuf(stdout, NULL);
 
+	/*
+	 * Without a PMD-order page cache folio the kernel refuses these
+	 * collapses, so there is nothing to test.
+	 */
+	if (!(thp_file_supported_orders() & (1UL << hpage_pmd_order))) {
+		if (shmem_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping shmem\n");
+			shmem_ops = NULL;
+		}
+		if (read_only_file_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping file\n");
+			read_only_file_ops = NULL;
+			read_write_file_read_ops = NULL;
+			read_write_file_write_ops = NULL;
+		}
+		if (!anon_ops && !shmem_ops && !read_only_file_ops)
+			ksft_exit_skip("No mem_type left to run\n");
+	}
+
 	default_settings.khugepaged.max_ptes_none = hpage_pmd_nr - 1;
 	default_settings.khugepaged.max_ptes_swap = hpage_pmd_nr / 8;
 	default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2;
_

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