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 <[email protected]>
---
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);
