On 9/15/26 5:21 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, change the khugepaged setting from ALWAYS to MADVICE for
the affected tests, and mark the VMA with MADV_NOHUGEPAGE after it has been
collapsed by wait_for_scan(). 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 | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index c32244b565658..83e9386bbc842 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -578,6 +578,8 @@ static bool wait_for_scan(const char *msg, char *p, size_t
len,
usleep(TICK);
}
+ madvise(p, len, MADV_NOHUGEPAGE);
This looks incorrect to me and would reintroduce the previous problem.
Please see commit 7962e05a835f ("selftests: khugepaged: fix the shmem
collapse failure").
+
return timeout == -1;
}
@@ -839,6 +841,7 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op
static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *ops)
{
+ struct thp_settings settings = *thp_current_settings();
int max_ptes_swap = thp_read_num("khugepaged/max_ptes_swap");
void *p;
@@ -860,6 +863,9 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o
validate_memory(p, 0, hpage_pmd_size);
if (c->enforce_pte_scan_limits) {
+ settings.hugepages[collapse_order].enabled = THP_MADVISE;
+ thp_push_settings(&settings);
I'm not sure why the collapse_order setting needs to be changed here. In
your test case, you did not use the '-c' parameter to specify the
collapse order.
+
ops->fault(p, 0, hpage_pmd_size);
ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap,
hpage_pmd_nr);
@@ -869,12 +875,15 @@ static void collapse_max_ptes_swap(struct
collapse_context *c, struct mem_ops *o
success("OK");
} else {
fail("Fail");
+ thp_pop_settings();
goto out;
}
c->collapse("Collapse with max_ptes_swap pages swapped out", p,
1, ops, true);
validate_memory(p, 0, hpage_pmd_size);
+
+ thp_pop_settings();
}
out:
ops->cleanup_area(p, hpage_pmd_size);
@@ -1075,6 +1084,7 @@ static void collapse_fork_compound(struct
collapse_context *c, struct mem_ops *o
static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops *ops)
{
+ struct thp_settings settings = *thp_current_settings();
int max_ptes_shared = thp_read_num("khugepaged/max_ptes_shared");
int wstatus;
void *p;
@@ -1100,6 +1110,9 @@ static void collapse_max_ptes_shared(struct
collapse_context *c, struct mem_ops
1, ops, !c->enforce_pte_scan_limits);
if (c->enforce_pte_scan_limits) {
+ settings.hugepages[collapse_order].enabled =
THP_MADVISE;
+ thp_push_settings(&settings);
Ditto.
+
ksft_print_msg("Trigger CoW on page %d of %d...",
hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr);
ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared) *
@@ -1111,6 +1124,8 @@ static void collapse_max_ptes_shared(struct
collapse_context *c, struct mem_ops
c->collapse("Collapse with max_ptes_shared PTEs shared",
p, 1, ops, true);
+
+ thp_pop_settings();
}
validate_memory(p, 0, hpage_pmd_size);
