On 9/21/26 6:35 PM, Yeoreum Yun wrote:
There are intermittent failures in collapse_max_ptes_swap() and
collapse_max_ptes_shared() when using the khugepaged_context:
// while running ./khugepaged -s 2
# Run test: collapse_max_ptes_shared (khugepaged:anon)
# Allocate huge page... OK
# Share huge page over fork()... OK
# Trigger CoW on page 1023 of 2048... OK
# Maybe collapse with max_ptes_shared exceeded.... OK
# Trigger CoW on page 1024 of 2048... Fail
Bail out! Unexpected huge page
# Planned tests != run tests (26 != 23)
# Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
# Run test: collapse_max_ptes_swap (khugepaged:anon)
# Swapout 257 of 2048 pages... OK
# Maybe collapse with max_ptes_swap exceeded.... OK
# Swapout 256 of 2048 pages... OK
Bail out! Unexpected huge page
# Planned tests != run tests (26 != 17)
# Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
This happens because khugepaged may collapse the pages before wait_for_scan()
is called, causing a sanity check that expects uncollapsed pages to fail.
For example, in collapse_max_ptes_swap(), after faulting the pages back in
and paging out up to max_ptes_swap pages, khugepaged may collapse them again
before c->collapse() is called.
To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been
collapsed by wait_for_scan() for anon. This prevents khugepaged from
collapsing it again before c->collapse() is called.
This failure was observed on NVIDIA Spark with 16KB page.
Signed-off-by: Yeoreum Yun <[email protected]>
---
tools/testing/selftests/mm/khugepaged.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index c32244b565658..1aad4bb427ece 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t
len,
usleep(TICK);
}
+ if (!strncmp(ops->name, "anon", 4))
We usually use the 'if (ops == &__anon_ops)' check in this file to
identify anonymous test cases.
With that, LGTM.
Reviewed-by: Baolin Wang <[email protected]>
Tested-by: Baolin Wang <[email protected]>
+ madvise(p, len, MADV_NOHUGEPAGE);
+
return timeout == -1;
}
