On 13/06/25 7:19 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 ("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 <z...@nvidia.com>
Signed-off-by: Baolin Wang <baolin.w...@linux.alibaba.com>
---
The test converts from fail to pass for me, for the aforementioned failures.
Reviewed-by: Dev Jain <dev.j...@arm.com>
Tested-by: Dev Jain <dev.j...@arm.com>
