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); + 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); + 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); + 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); -- 2.43.0
