On 8/23/26 20:43, Zenghui Yu wrote: > From: "Zenghui Yu (Huawei)" <[email protected]> > > 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
How did you reproduce this? Is this an actual test result? ~/linux/tools/testing/selftests/mm$ cat /sys/kernel/mm/ksm/smart_scan 1 ~/linux/tools/testing/selftests/mm$ sudo ./ksm_tests -N -d TAP version 13 1..1 pages_shared : 1 pages_sharing : 1 max_page_sharing : 256 full_scans : 1283 pages_unshared : 0 pages_volatile : 0 stable_node_chains: 0 stable_node_dups : 0 general_profit : 3968 ksm_rmap_items 2 ksm_zero_pages 0 ksm_merging_pages 2 ksm_process_profit 8064 ksm_merge_any: no ksm_mergeable: yes ok 1 KSM NUMA merging # Totals: pass:1 fail:0 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 How is that supposed to happen? The sequence we have is: numa1_map_ptr = numa_alloc_onnode(page_size, first_node); numa2_map_ptr = numa_alloc_onnode(page_size, second_node); ... memset(numa1_map_ptr, '*', page_size); memset(numa2_map_ptr, '*', page_size); ... if (ksm_merge_pages(merge_type, numa1_map_ptr, page_size, start_time, timeout) ... KSM smart scan operates on rmap entries. rmap entries are per MM. -- Cheers, David
