From: "Kiryl Shutsemau (Meta)" <[email protected]> The harness pins max_ptes_none to 0, so khugepaged only collapses a window once every PTE in it is present. A window with holes takes a different route, and never gets raced. A hole is zero-filled in the new folio rather than copied. Which slots count as holes keeps moving under the racing MADV_DONTNEED, right up to the moment the PMD is detached.
Run both ends of the occupancy scale for every driver mode, one after the other. mTHP collapse supports only those two, 0 and HPAGE_PMD_NR - 1, and coerces anything between them to 0. Each result says which end it ran: ok 1 stepped/strict: 5s, 231 steps, no corruption ok 2 stepped/holes: 5s, 194 steps, no corruption Assisted-by: LLM Tested-by: Muhammad Usama Anjum <[email protected]> Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]> --- tools/testing/selftests/mm/khugepaged_race.c | 32 ++++++++++++-------- 1 file changed, 20 insertions(+), 12 deletions(-) diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c index 448256704ef4..f31f12fc0390 100644 --- a/tools/testing/selftests/mm/khugepaged_race.c +++ b/tools/testing/selftests/mm/khugepaged_race.c @@ -231,6 +231,8 @@ int main(int argc, char **argv) const int nr_threads = ARRAY_SIZE(thread_names); pthread_t threads[ARRAY_SIZE(thread_names)]; static const char * const all_modes[] = { "stepped", "free", "madvise" }; + static const bool occupancies[] = { false, true }; /* strict, holes */ + const int nr_occupancies = ARRAY_SIZE(occupancies); const char *one_mode[1]; const char * const *modes = all_modes; int nr_modes = ARRAY_SIZE(all_modes); @@ -298,7 +300,7 @@ int main(int argc, char **argv) -1, 0) != (void *)mremap_scratch) ksft_exit_fail_perror("mmap() mremap scratch"); - ksft_set_plan(nr_modes); + ksft_set_plan(nr_modes * nr_occupancies); thp_save_settings(); thp_read_settings(&settings); @@ -306,8 +308,9 @@ int main(int argc, char **argv) /* Base of the settings stack; the bottom entry is never popped */ thp_push_settings(&settings); - for (int m = 0; m < nr_modes; m++) { - const char *mode = modes[m]; + for (int run = 0; run < nr_modes * nr_occupancies; run++) { + const char *mode = modes[run / nr_occupancies]; + bool holes = occupancies[run % nr_occupancies]; thp_read_settings(&settings); settings.thp_enabled = THP_MADVISE; @@ -317,12 +320,14 @@ int main(int argc, char **argv) settings.khugepaged.scan_sleep_millisecs = strcmp(mode, "free") ? 1000 : 0; settings.khugepaged.alloc_sleep_millisecs = 10; + /* - * mTHP collapse honours only 0 or HPAGE_PMD_NR - 1 here, and 0 - * keeps a step from being spent on PMD allocations that racing - * MADV_DONTNEED will not let succeed. + * mTHP collapse honours only 0 or HPAGE_PMD_NR - 1 here. The two + * ends race different paths: a strict window has every PTE + * present, a hole-heavy one is mostly zero-filled. */ - settings.khugepaged.max_ptes_none = 0; + settings.khugepaged.max_ptes_none = holes ? + (hpage_pmd_size / page_size) - 1 : 0; /* One wake, one pass: the playground plus the forked children's copies */ settings.khugepaged.pages_to_scan = nr_areas * (hpage_pmd_size / page_size) * 8; @@ -388,8 +393,9 @@ int main(int argc, char **argv) check_page(i); ksft_test_result(!corrupted, - "%s: %ds, %d steps, no corruption\n", - mode, duration_s, steps); + "%s/%s: %ds, %d steps, no corruption\n", + mode, holes ? "holes" : "strict", + duration_s, steps); /* The next mode maps the same fixed address with its own settings */ munmap(region, nr_areas * hpage_pmd_size); @@ -399,9 +405,11 @@ int main(int argc, char **argv) if (corrupted) { /* Memory is suspect; the rest would prove nothing */ - while (++m < nr_modes) - ksft_test_result_skip("%s: skipped after corruption\n", - modes[m]); + while (++run < nr_modes * nr_occupancies) + ksft_test_result_skip("%s/%s: skipped after corruption\n", + modes[run / nr_occupancies], + occupancies[run % nr_occupancies] ? + "holes" : "strict"); break; } } -- 2.54.0
