+ selftests-mm-skip-collapse_compound_extreme-on-thp-allocation-failure.patch added to mm-new branch

+ selftests-mm-skip-collapse_compound_extreme-on-thp-allocation-failure.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: skip collapse_compound_extreme() on THP allocation failure
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-skip-collapse_compound_extreme-on-thp-allocation-failure.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-collapse_compound_extreme-on-thp-allocation-failure.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

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------------------------------------------------------
From: "Zenghui Yu (Huawei)" <zenghui.yu@linux.dev>
Subject: selftests/mm: skip collapse_compound_extreme() on THP allocation failure
Date: Wed, 28 Oct 2026 18:01:19 +0800

collapse_compound_extreme() needs hpage_pmd_nr PMD-order allocations in a
row, and it kills the whole test binary via ksft_exit_fail_msg() as soon
as one of them fails.

Gating the case by PMD size (commit b36bec6a01b1) -- the current
workaround for arm64 with 64K base pages, where a 512M PMD makes every
construction step an order-13 allocation -- is not enough: the case still
dies below the cutoff, e.g.  on an arm64 VM with 16K base pages and 8G of
RAM, where the construction would need ~64G worth of PMD-order
allocations.

Remove the PMD-size gating and treat a failure to allocate a huge page
during the construction as a skip: whether the allocator can hand out that
many PMD-order folios in a row depends on the memory available on the
machine, not on the kernel.

Link: https://lore.kernel.org/20261028100119.11340-1-zenghui.yu@linux.dev
Signed-off-by: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Link: https://lore.kernel.org/all/atiQmWnz8zx2AKI7@thinkstation
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
---

 tools/testing/selftests/mm/khugepaged.c |   26 +++++++++++-----------
 1 file changed, 14 insertions(+), 12 deletions(-)

--- a/tools/testing/selftests/mm/khugepaged.c~selftests-mm-skip-collapse_compound_extreme-on-thp-allocation-failure
+++ a/tools/testing/selftests/mm/khugepaged.c
@@ -953,23 +953,25 @@ static void collapse_compound_extreme(st
 	void *p;
 	int i;
 
-	/*
-	 * This needs hpage_pmd_nr PMD-order allocations in a row, which the
-	 * allocator will not supply if the PMD is very large.
-	 */
-	if (hpage_pmd_size > (32UL << 20)) {
-		ksft_test_result_skip("%s: PMD too large for fault-time THP construction\n",
-				      __func__);
-		return;
-	}
-
 	p = ops->setup_area(1);
 	ksft_print_msg("Construct PTE page table full of different PTE-mapped compound pages\n");
 	for (i = 0; i < hpage_pmd_nr; i++) {
 		madvise(BASE_ADDR, hpage_pmd_size, MADV_HUGEPAGE);
 		ops->fault(BASE_ADDR, 0, hpage_pmd_size);
-		if (!ops->check_huge(BASE_ADDR, hpage_pmd_size, 1, hpage_pmd_size))
-			ksft_exit_fail_msg("Failed to allocate huge page\n");
+		if (!ops->check_huge(BASE_ADDR, hpage_pmd_size, 1, hpage_pmd_size)) {
+			/*
+			 * Constructing the PTE table requires hpage_pmd_nr
+			 * PMD-order allocations in a row.  Whether the
+			 * allocator can supply them depends on the memory
+			 * available on the machine, not on the kernel: skip
+			 * instead of failing the test run.
+			 */
+			ops->cleanup_area(BASE_ADDR - i * page_size,
+					  i * page_size + hpage_pmd_size);
+			ksft_test_result_skip("%s: Failed to allocate huge page\n",
+					      __func__);
+			return;
+		}
 		madvise(BASE_ADDR, hpage_pmd_size, MADV_NOHUGEPAGE);
 
 		p = mremap(BASE_ADDR - i * page_size,
_

Patches currently in -mm which might be from zenghui.yu@linux.dev are

mm-page_alloc-mark-pages-freed-by-__free_pages_core-as-not-tagged.patch
selftests-mm-fix-khugepaged_race-build-with-older-glibc.patch
selftests-mm-skip-collapse_compound_extreme-on-thp-allocation-failure.patch