There are intermittent failures in collapse_max_ptes_swap() and collapse_max_ptes_shared() when using the khugepaged_context:
# 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. Also, fix false-positive results when a child process fails in tests such as collapse_fork*() or collapse_max_ptes_shared(): # ------------------------- # 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 // child failed. # Check if parent still has huge page... OK // parent hpage success ok 24 collapse_max_ptes_shared // considered as success ... # Totals: pass:26 fail:0 xfail:0 xpass:0 skip:0 error:0 This failure was observed on NVIDIA Spark with 16KB page and this patch is based on mm/mm-unstable --- Changes in v2: - remove temporary enabled setup. - Link to v1: https://lore.kernel.org/r/[email protected] --- Yeoreum Yun (2): kselftest: mm: return fail when child test result is fail in khugepaged kselftest: mm: fix intermittent failure khugepaged test tools/testing/selftests/mm/khugepaged.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) --- base-commit: 8d61431ed2607386b427752505379536eb634ce8 change-id: 20260915-fix_khugepagd_fail-9d8932689200 Best regards, -- Sincerely, Yeoreum Yun
