From: "Zenghui Yu (Huawei)" The "KSM NUMA merging" test allocates two identical pages on two NUMA nodes and verifies KSM will merge these two pages after 2 scans (see ksm_merge_pages()). But when smart scan is enabled, pages that have previously not been de-duplicated may get skipped for some scans. Verifying KSM behavior after only 2 scans may not be enough. $ ./ksm_tests -N -d TAP version 13 1..1 pages_shared : 0 pages_sharing : 0 max_page_sharing : 256 full_scans : 211 pages_unshared : 1 pages_volatile : 2 stable_node_chains: 0 stable_node_dups : 0 general_profit : -128 ksm_rmap_items 2 ksm_zero_pages 0 ksm_merging_pages 0 ksm_process_profit -128 ksm_merge_any: no ksm_mergeable: yes not ok 1 KSM NUMA merging # Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0 This specific test fails because KSM started scanning the second page whilst the first page had already been scanned for 16 times (ksm_rmap_item::age of page 0 is 16 greater than page 1). It's not difficult to infer that should_skip_rmap_item() cannot be false at the same time for these two pages - they cannot be merged even after 211 full scans. Given the current implementation of smart scan, it may not be appropriate to enable it for selftests. Let's disable it for now. Signed-off-by: Zenghui Yu (Huawei) --- tools/testing/selftests/mm/ksm_tests.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c index 5fd7792a0d47..e72681090ff9 100644 --- a/tools/testing/selftests/mm/ksm_tests.c +++ b/tools/testing/selftests/mm/ksm_tests.c @@ -33,6 +33,7 @@ struct ksm_sysfs { unsigned long pages_to_scan; unsigned long run; unsigned long sleep_millisecs; + unsigned long smart_scan; unsigned long stable_node_chains_prune_millisecs; unsigned long use_zero_pages; }; @@ -293,6 +294,7 @@ static int ksm_save_def(struct ksm_sysfs *ksm_sysfs) ksm_read_sysfs(KSM_FP("sleep_millisecs"), &ksm_sysfs->sleep_millisecs) || ksm_read_sysfs(KSM_FP("pages_to_scan"), &ksm_sysfs->pages_to_scan) || ksm_read_sysfs(KSM_FP("run"), &ksm_sysfs->run) || + ksm_read_sysfs(KSM_FP("smart_scan"), &ksm_sysfs->smart_scan) || ksm_read_sysfs(KSM_FP("stable_node_chains_prune_millisecs"), &ksm_sysfs->stable_node_chains_prune_millisecs) || ksm_read_sysfs(KSM_FP("use_zero_pages"), &ksm_sysfs->use_zero_pages)) @@ -309,6 +311,7 @@ static int ksm_restore(struct ksm_sysfs *ksm_sysfs) ksm_write_sysfs(KSM_FP("pages_to_scan"), ksm_sysfs->pages_to_scan) || ksm_write_sysfs(KSM_FP("run"), ksm_sysfs->run) || ksm_write_sysfs(KSM_FP("sleep_millisecs"), ksm_sysfs->sleep_millisecs) || + ksm_write_sysfs(KSM_FP("smart_scan"), ksm_sysfs->smart_scan) || ksm_write_sysfs(KSM_FP("stable_node_chains_prune_millisecs"), ksm_sysfs->stable_node_chains_prune_millisecs) || ksm_write_sysfs(KSM_FP("use_zero_pages"), ksm_sysfs->use_zero_pages)) @@ -846,6 +849,7 @@ int main(int argc, char *argv[]) if (ksm_write_sysfs(KSM_FP("run"), 2) || ksm_write_sysfs(KSM_FP("sleep_millisecs"), 0) || + ksm_write_sysfs(KSM_FP("smart_scan"), 0) || (numa_available() ? 0 : ksm_write_sysfs(KSM_FP("merge_across_nodes"), 1)) || ksm_write_sysfs(KSM_FP("pages_to_scan"), page_count)) -- 2.53.0