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.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the hw/process/vma") Reviewed-by: Zi Yan ziy@nvidia.com Signed-off-by: Baolin Wang baolin.wang@linux.alibaba.com --- Changes from v1: - Add reviewed tag from Zi. Thanks. - Drop the MADV_NOHUGEPAGE setting, per David. --- tools/testing/selftests/mm/khugepaged.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c index 8a4d34cce36b..4341ce6b3b38 100644 --- a/tools/testing/selftests/mm/khugepaged.c +++ b/tools/testing/selftests/mm/khugepaged.c @@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char *p, int nr_hpages, usleep(TICK); }
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE); - return timeout == -1; }