On 2025/6/12 13:10, Dev Jain wrote:
On 12/06/25 9:24 am, Baolin Wang wrote:
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, PMD mappings are prevented if the VMA is set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings during refault.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem refault. With this fix, the shmem test case passes.
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
tools/testing/selftests/mm/khugepaged.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c index 8a4d34cce36b..d462f62d8116 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; } @@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages, if (ops != &__anon_ops) ops->fault(p, 0, nr_hpages * hpage_pmd_size); + madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE); if (ops->check_huge(p, expect ? nr_hpages : 0)) success("OK"); else
The idea looks sane to me, but do we need to add the madvise call to madvise_retracted_page_tables() too, since that also calls wait_for_scan()?
Yes, I also realized this after sending the patches:) Thanks.
To keep the original logic:
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c index d462f62d8116..3452763e2fe3 100644 --- a/tools/testing/selftests/mm/khugepaged.c +++ b/tools/testing/selftests/mm/khugepaged.c @@ -1074,6 +1074,7 @@ static void madvise_retracted_page_tables(struct collapse_context *c, return; } success("OK"); + madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE); c->collapse("Install huge PMD from page cache", p, nr_hpages, ops, true); validate_memory(p, 0, size);