[merged mm-stable] selftests-khugepaged-fix-the-shmem-collapse-failure.patch removed from -mm tree

[merged mm-stable] selftests-khugepaged-fix-the-shmem-collapse-failure.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: selftests: khugepaged: fix the shmem collapse failure
has been removed from the -mm tree.  Its filename was
     selftests-khugepaged-fix-the-shmem-collapse-failure.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: selftests: khugepaged: fix the shmem collapse failure
Date: Fri, 13 Jun 2025 09:49:19 +0800

When running the khugepaged selftest for shmem (./khugepaged all:shmem), I
encountered the following test failures:

: Run test: collapse_full (khugepaged:shmem)
: Collapse multiple fully populated PTE table.... Fail
: ...
: Run test: collapse_single_pte_entry (khugepaged:shmem)
: Collapse PTE table with single PTE entry present.... Fail
: ...
: Run test: collapse_full_of_compound (khugepaged:shmem)
: Allocate huge page... OK
: Split huge page leaving single PTE page table full of compound pages... OK
: Collapse PTE table full of compound pages.... Fail

The reason for the failure is that it will set MADV_NOHUGEPAGE to prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function.  Moreover, shmem requires a
refault to establish PMD mappings.

However, after commit 2b0f922323cc ("mm: don't install PMD mappings when
THPs are disabled by the hw/process/vma"), PMD mappings are prevented if
the VMA is set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD
mappings during refault.

One way to fix this issue is to move the MADV_NOHUGEPAGE setting after the
shmem refault.  After shmem refault and check huge, the test case will
unmap the shmem immediately.  So it seems unnecessary to set the
MADV_NOHUGEPAGE.

Then we can simply drop the MADV_NOHUGEPAGE setting, and all khugepaged
test cases passed.

Link: https://lkml.kernel.org/r/d8502fc50d0304c2afd27ced062b1d636b7a872e.1749779183.git.baolin.wang@linux.alibaba.com
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the hw/process/vma")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Tested-by: Dev Jain <dev.jain@arm.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/khugepaged.c |    2 --
 1 file changed, 2 deletions(-)

--- a/tools/testing/selftests/mm/khugepaged.c~selftests-khugepaged-fix-the-shmem-collapse-failure
+++ a/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *ms
 		usleep(TICK);
 	}
 
-	madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
 	return timeout == -1;
 }
 
_

Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are

khugepaged-allow-khugepaged-to-check-all-anonymous-mthp-orders.patch
khugepaged-kick-khugepaged-for-enabling-none-pmd-sized-mthps.patch
mm-fault-in-complete-folios-instead-of-individual-pages-for-tmpfs.patch