Re: [patch v5] mm: vmstat_kunit: add synthetic benchmark for mm stats

["David Hildenbrand (Arm)" <david@kernel.org>]

On 10/17/26 00:35, David Rientjes wrote:
> On Fri, 9 Oct 2026, David Rientjes wrote:
> 
>> From: Christoph Lameter <cl@gentwo.org>
>>
>> Add a synthetic benchmark that can be used to measure performance of MM
>> statistics.  This is used to analyze any improvements or regressions in
>> functions that are frequently used in hot code paths.
>>
>> This is the first of three tests that measure the execution times of
>> critical MM functions anticipated to be used by developers to measure the
>> impact of any core changes that would end up causing workload performance
>> issues.  Vmstats are embedded into MM hotpaths, so any regression can
>> cause performance and scalability impact for users.  Google has carried
>> these tests internally and kept them updated since Christoph posted them
>> back in 2009 for this purpose.
>>
>> This can also be used to detect regressions over time, from kernel
>> version to kernel version, independent of development use cases.
>>
>> The test is run by KUnit or doing modprobe vmstat_kunit directly.
>>
>> Sample output:
>>  KTAP version 1
>>  1..1
>>  KTAP version 1
>>  # Subtest: vmstat
>>  # module: vmstat_kunit
>>       1..3
>>       # vmstat_test_inc_dec_zone_page_state: 10000 ops: inc_zone_page_state -> 8 cycles (4 ns/op), dec_zone_page_state -> 9 cycles (4 ns/op)
>>       ok 1 vmstat_test_inc_dec_zone_page_state
>>       # vmstat_test_interleaved_zone_page_state: 10000 ops: inc/dec pair -> 17 cycles (8 ns/op)
>>       ok 2 vmstat_test_interleaved_zone_page_state
>>       # vmstat_test_count_vm_event: 10000 ops: count_vm_event -> 4 cycles (2 ns/op)
>>       ok 3 vmstat_test_count_vm_event
>>  # vmstat: pass:3 fail:0 skip:0 total:3
>>  # Totals: pass:3 fail:0 skip:0 total:3
>>  ok 1 vmstat
>>
>> Assisted-by: Gemini:gemini-3.8-flash
>> Signed-off-by: Christoph Lameter <cl@gentwo.org>
>> Signed-off-by: David Rientjes <rientjes@google.com>
>> ---
>> v5:
>>  - added dependency on CONFIG_VM_EVENT_COUNTERS
>>  - expanded commit description
>>
>> Once we're happy with this change, I'll apply the same treatment to the
>> proposed pgalloc and slab tests.
>>
> 
> I've added the rationale for the change to the commit description as 
> primairly being used by developers to benchmark and monitor any 
> regressions in functions that are known to be super hot and impact 
> workload performance.
> 
> This is the simplest of the three tests that Christoph provided back in 
> 2009, the others are pgalloc and slab tests, see 
> https://marc.info/?l=linux-mm&m=178547194364290 and 
> https://marc.info/?l=linux-mm&m=178547193264283 for those.  Based on the 
> feedback to move to kunit, I forked this one off independently because it 
> was the simplest to address all the feedback and pave the way for the 
> other two to be upstreamed afterwards.
> 
> Is this acceptable for merge?  If we're happy with this, I'll move onto 
> the pgalloc and slab variants.

Works for me. The tests are rather small and I see value in them.


-- 
Cheers,

David