Re: [PATCH v3 2/3] selftests/mm: fix ksm NUMA merge test for systems with memoryless NUMA nodes

[Usama Arif <usama.arif@linux.dev>]

On Wed,  8 Jul 2026 12:29:06 +0530 Sayali Patil <sayalip@linux.ibm.com> wrote:

> The KSM NUMA merge test allocates identical pages on different NUMA
> nodes and verifies KSM behavior with merge_across_nodes enabled and
> disabled.
> 
> On systems with memoryless NUMA nodes, for example:
>  #numactl  -H
>       available: 2 nodes (0,4)
>       .....
>       node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
>       node 0 size: 14825 MB
>       node 0 free: 1382 MB
>       node 4 cpus:
>       node 4 size: 0 MB
>       node 4 free: 0 MB
> 
> the test may attempt to allocate memory on a node without memory,
> causing numa_alloc_onnode() to fail and resulting in a spurious test
> failure.
> 
> The test currently checks numa_num_configured_nodes() to determine
> whether sufficient NUMA nodes are available. However, configured nodes
> do not necessarily have memory.
> 
> Reuse the existing get_first_mem_node() and get_next_mem_node()
> helpers to locate NUMA nodes that actually contain memory, and skip
> the test when fewer than two such nodes are available.
> 
> Before patch:
>        ---------------------------
> 	running ./ksm_tests -N -m 1
>        ---------------------------
>         mbind: Invalid argument
>         ok 1 KSM NUMA merging
> 	Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
>         [PASS]
>        ok 1 ksm_tests -N -m 1
>        ---------------------------
>         running ./ksm_tests -N -m 0
>        ---------------------------
>         mbind: Invalid argument
>         not ok 1 KSM NUMA merging
> 	Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0
>         [FAIL]
>        not ok 2 ksm_tests -N -m 0 # exit=1
> 
> After patch:
>        ---------------------------
>         running ./ksm_tests -N -m 1
>        ---------------------------
>         At least 2 NUMA nodes with memory must be available
> 	ok 1
> 	SKIP KSM NUMA merging
> 	Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
>         [PASS]
>         ok 1 ksm_tests -N -m 1
>        ---------------------------
>         running ./ksm_tests -N -m 0
>        ---------------------------
>         At least 2 NUMA nodes with memory must be available
> 	ok 1
> 	SKIP KSM NUMA merging
> 	Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
>         [PASS]
>         ok 2 ksm_tests -N -m 0
> 
> Fixes: e3820ab252dd ("selftest/vm: fix ksm selftest to run with different NUMA topologies")
> Co-developed-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
> ---
>  tools/testing/selftests/mm/ksm_tests.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 

Acked-by: Usama Arif <usama.arif@linux.dev>