From: "Kiryl Shutsemau (Meta)" <[email protected]> The harness races collapse against faults, pins, fork, mremap and MADV_DONTNEED, but nothing in it elevates a source folio's refcount from the reclaim or compaction side.
Add two more threads, and run every mode and occupancy limit both with and without them: - pageout: cycles MADV_PAGEOUT over a dedicated neighbour region, faults it back in and checks the content each round, since a page's pattern must survive the trip through swap. Idle when the host has no swap, because then there is no anon reclaim to drive. - compactor: writes /proc/sys/vm/compact_memory in a loop. Compaction isolates and migrates folios, so it competes with a collapse for the pages it is gathering, with refcount elevations and migration entries of its own. -p narrows a run to the combinations that have them, the way -z narrows the occupancy and -m the mode. Each result says which it ran: ok 2 stepped/strict/pressure: 5s, 88 steps, no corruption Assisted-by: Claude-Code:claude-opus-5 Signed-off-by: Kiryl Shutsemau (Meta) <[email protected]> --- tools/testing/selftests/mm/khugepaged_race.c | 147 +++++++++++++++++-- 1 file changed, 136 insertions(+), 11 deletions(-) diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c index a2a91906285b..abd142db7cbe 100644 --- a/tools/testing/selftests/mm/khugepaged_race.c +++ b/tools/testing/selftests/mm/khugepaged_race.c @@ -18,6 +18,12 @@ * zero-filled, and re-checked under the page table lock at install time in * case a racing fault got there first. * + * -p adds memory pressure to any of the above: MADV_PAGEOUT cycling + * on a dedicated neighbor region (swap traffic and LRU churn; skipped + * with a note when the host has no swap) and a compact_memory trigger + * loop (compaction migrates source folios, racing collapse's freeze + * with refcount elevation and migration entries of its own). + * * Correctness signals: every racing page must read as its pattern or * zero (MADV_DONTNEED), never anything else. The faulters and the fork * children check that continuously, a final sweep checks it once more, plus @@ -61,6 +67,8 @@ static unsigned long page_size; static char *region; /* NR_AREAS * hpage_pmd_size */ static char *mremap_area; /* region + NR_SHARED_AREAS areas */ static char *mremap_scratch; /* well above the region */ +static char *pageout_area; /* -p: dedicated pressure region */ +static size_t pageout_size; static int gup_fd = -1; static volatile int stop; static volatile int corrupted; @@ -188,6 +196,70 @@ static void *mremapper_fn(void *arg) return NULL; } +/* + * -p: swap traffic and LRU churn on a region of our own. The content + * check is exact: a page out and back through swap must preserve the + * pattern, and nothing else ever writes here. + */ +static void *pageout_fn(void *arg) +{ + unsigned int seed = (unsigned long)arg; + unsigned long nr = pageout_size / page_size; + unsigned long i; + + for (i = 0; i < nr; i++) + *(unsigned int *)(pageout_area + i * page_size) = pattern(i); + + while (!stop) { + madvise(pageout_area, pageout_size, MADV_PAGEOUT); + for (i = 0; i < nr && !stop; i++) { + unsigned int val = *(unsigned int *)(pageout_area + + i * page_size); + + if (val != pattern(i)) { + corrupted = 1; + ksft_print_msg("Pageout corruption at page %lu: %#x != %#x\n", + i, val, pattern(i)); + } + } + usleep(rand_r(&seed) % 2000); + } + return NULL; +} + +/* -p: compaction migrates the collapse sources out from under us. */ +static void *compactor_fn(void *arg) +{ + unsigned int seed = (unsigned long)arg; + int fd = open("/proc/sys/vm/compact_memory", O_WRONLY); + + if (fd < 0) { + ksft_print_msg("No compact_memory; compactor idle\n"); + return NULL; + } + while (!stop) { + if (write(fd, "1", 1) < 0) + break; + usleep(10000 + rand_r(&seed) % 100000); + } + close(fd); + return NULL; +} + +static bool swap_available(void) +{ + char line[256]; + int lines = 0; + FILE *fp = fopen("/proc/swaps", "r"); + + if (!fp) + return false; + while (fgets(line, sizeof(line), fp)) + lines++; + fclose(fp); + return lines > 1; +} + static unsigned long now_ms(void) { struct timeval tv; @@ -199,11 +271,14 @@ static unsigned long now_ms(void) static void usage(void) { fprintf(stderr, - "Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-z] [-a areas]\n" + "Usage: khugepaged_race [-d seconds] [-m stepped|free|madvise] [-z] [-p] [-a areas]\n" "\tWithout -m, every mode runs in turn.\n" "\t-d: seconds per mode (default 5)\n" "\tBoth occupancy limits run unless -z asks for holes only.\n" "\t-z: only max_ptes_none = HPAGE_PMD_NR - 1 (hole-heavy)\n" + "\tRuns with and without memory pressure unless -p asks for\n" + "\tpressure only.\n" + "\t-p: only with the pageout and compaction threads\n" "\t-a: number of shared PMD-sized playground areas (default 3)\n"); exit(1); } @@ -212,18 +287,22 @@ int main(int argc, char **argv) { static const char * const thread_names[] = { "faulter", "faulter2", "dontneed", "pinner", "forker", - "mremapper", + "mremapper", "pageout", "compactor", }; void *(*const thread_fns[])(void *) = { faulter_fn, faulter_fn, dontneed_fn, pinner_fn, forker_fn, - mremapper_fn, + mremapper_fn, pageout_fn, compactor_fn, }; + const unsigned long pageout_bit = 1UL << 6, compactor_bit = 1UL << 7; 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 int all_nones[] = { 0, 1 }; /* strict, holes */ + static const int all_press[] = { 0, 1 }; /* quiet, under pressure */ const int *nones = all_nones; + const int *press = all_press; int nr_nones = ARRAY_SIZE(all_nones); + int nr_press = ARRAY_SIZE(all_press); const char *one_mode[1]; const char * const *modes = all_modes; int nr_modes = ARRAY_SIZE(all_modes); @@ -232,13 +311,15 @@ int main(int argc, char **argv) unsigned long end_ms; int duration_s = 5; unsigned long thread_mask = ~0UL; + unsigned long base_mask; int nr_areas_arg = 0; bool holes_only = false; + bool pressure_only = false; unsigned long i; int steps = 0; int opt; - while ((opt = getopt(argc, argv, "a:d:m:t:zh")) != -1) { + while ((opt = getopt(argc, argv, "a:d:m:t:zph")) != -1) { switch (opt) { case 'a': nr_areas_arg = atoi(optarg); @@ -256,6 +337,9 @@ int main(int argc, char **argv) case 'z': holes_only = true; break; + case 'p': + pressure_only = true; + break; default: usage(); } @@ -265,6 +349,11 @@ int main(int argc, char **argv) nr_nones = 1; } + if (pressure_only) { + press = all_press + 1; + nr_press = 1; + } + if (mode_arg) { if (strcmp(mode_arg, "stepped") && strcmp(mode_arg, "free") && strcmp(mode_arg, "madvise")) @@ -304,7 +393,12 @@ int main(int argc, char **argv) -1, 0) != (void *)mremap_scratch) ksft_exit_fail_perror("mmap() mremap scratch"); - ksft_set_plan(nr_modes * nr_nones); + base_mask = thread_mask; + if (!swap_available()) + /* No swap, no anon reclaim: compaction-only pressure. */ + ksft_print_msg("no swap: the pageout thread stays idle\n"); + + ksft_set_plan(nr_modes * nr_nones * nr_press); thp_save_settings(); thp_read_settings(&settings); @@ -316,9 +410,17 @@ int main(int argc, char **argv) */ thp_push_settings(&settings); - for (int mn = 0; mn < nr_modes * nr_nones; mn++) { - const char *mode = modes[mn / nr_nones]; - bool holes = nones[mn % nr_nones]; + for (int run = 0; run < nr_modes * nr_nones * nr_press; run++) { + int rem = run % (nr_nones * nr_press); + const char *mode = modes[run / (nr_nones * nr_press)]; + bool holes = nones[rem / nr_press]; + bool pressure = press[rem % nr_press]; + + thread_mask = base_mask; + if (!pressure) + thread_mask &= ~(pageout_bit | compactor_bit); + else if (!swap_available()) + thread_mask &= ~pageout_bit; thp_read_settings(&settings); settings.thp_enabled = THP_MADVISE; @@ -354,6 +456,24 @@ int main(int argc, char **argv) ksft_exit_fail_perror("mmap() playground"); mremap_area = region + nr_shared_areas * hpage_pmd_size; + if (thread_mask & pageout_bit) { + /* + * Big enough to cycle real reclaim, small enough not + * to dominate a TCG guest: 4 PMD areas, clamped to + * [16M, 64M]. + */ + pageout_size = 4 * hpage_pmd_size; + pageout_size = pageout_size < (16UL << 20) ? + (16UL << 20) : + pageout_size > (64UL << 20) ? + (64UL << 20) : pageout_size; + pageout_area = mmap(NULL, pageout_size, + PROT_READ | PROT_WRITE, + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); + if (pageout_area == MAP_FAILED) + ksft_exit_fail_perror("mmap() pageout area"); + } + /* Populate so the first pass has something to collapse. */ for (i = 0; i < nr_shared_areas * hpage_pmd_size / page_size; i++) *(unsigned int *)(region + i * page_size) = pattern(i); @@ -403,8 +523,9 @@ int main(int argc, char **argv) check_page(i); ksft_test_result(!corrupted, - "%s/%s: %ds, %d steps, no corruption\n", + "%s/%s%s: %ds, %d steps, no corruption\n", mode, holes ? "holes" : "strict", + pressure ? "/pressure" : "", duration_s, steps); /* @@ -413,15 +534,19 @@ int main(int argc, char **argv) * and its scan cadence differs. */ munmap(region, nr_areas * hpage_pmd_size); + if (pageout_area) { + munmap(pageout_area, pageout_size); + pageout_area = NULL; + } thp_pop_settings(); stop = 0; steps = 0; if (corrupted) { /* Memory is suspect; the rest would prove nothing. */ - while (++mn < nr_modes * nr_nones) + while (++run < nr_modes * nr_nones * nr_press) ksft_test_result_skip("%s: skipped after corruption\n", - modes[mn / nr_nones]); + modes[run / (nr_nones * nr_press)]); break; } } -- 2.54.0
