Re: [PATCH v2] kselftest: mm: remove HPAGE_SIZE and HPAGE_SHIFT macro

[Sarthak Sharma <sarthak.sharma@arm.com>]

On 9/7/26 8:06 PM, David Hildenbrand (Arm) wrote:
> On 9/7/26 10:15, Yeoreum Yun wrote:
>> HPAGE_SIZE and HPAGE_SHIFT macro is written based on the 4KB PAGE_SIZE.
>> When this macro is used in some test, test result would be strange in
>> the system where PAGE_SIZE is more then 4KB.
>>
>> Here is the example with transhuge-stress test with 16KB PAGE_SIZE:
>>
>>   transhuge-stress: allocate 61073 transhuge pages, using 122146 MiB virtual memory and 1908 MiB of ram
>>     3.292 s/loop, 0.054 ms/page,  37106.002 MiB/s	2566 succeed, 58507 failed, 2566 different pages
>>     0.591 s/loop, 0.010 ms/page, 206850.792 MiB/s	   0 succeed, 61073 failed,    0 different pages
>>     0.527 s/loop, 0.009 ms/page, 231895.107 MiB/s	   0 succeed, 61073 failed,    0 different pages
>>     0.527 s/loop, 0.009 ms/page, 231839.704 MiB/s	   0 succeed, 61073 failed,    0 different pages
>>     0.528 s/loop, 0.009 ms/page, 231544.782 MiB/s	   0 succeed, 61073 failed,    0 different pages
>>     0.528 s/loop, 0.009 ms/page, 231462.074 MiB/s	   0 succeed, 61073 failed,    0 different pages
>>     0.527 s/loop, 0.009 ms/page, 231770.300 MiB/s	   0 succeed, 61073 failed,    0 different pages
>>     ...
>>   ok 1 Completed
>>
>> Remove the HPAGE_SIZE and HPAGE_SHIFT macros and introduce pmd_page_shift()
>> helper to get the HPAGE_SHIFT properly. For HPAGE_SIZE, use pre-existing
>> helper, read_pmd_pagesize().
>>
>> Also, run the KSM_MERGE_TIME_HUGE_PAGES test with a size of 512 MiB,
>> which is the least common multiple of the PMD sizes for 4 KiB, 16 KiB,
>> and 64 KiB base pages. Since allocate_transhuge() allocates mappings in
>> PMD-sized units, the test may fail with the previous size of 100 MiB,
>> which is not a multiple of the PMD size when the base page size is
>> 16 KiB or 64 KiB.
>>
>> After this patch, output of transhuge-stress:
>>
>>   transhuge-stress: allocate 3817 transhuge pages, using 122146 MiB virtual memory and 119 MiB of ram
>>     2.558 s/loop, 0.670 ms/page,  47755.759 MiB/s	2585 succeed, 1232 failed, 2585 different pages
>>     2.640 s/loop, 0.692 ms/page,  46268.432 MiB/s	2585 succeed, 1232 failed, 2585 different pages
>>     2.635 s/loop, 0.690 ms/page,  46360.298 MiB/s	2585 succeed, 1232 failed, 2585 different pages
>>     2.782 s/loop, 0.729 ms/page,  43899.795 MiB/s	2616 succeed, 1201 failed, 2616 different pages
>>     2.692 s/loop, 0.705 ms/page,  45380.876 MiB/s	2627 succeed, 1190 failed, 2627 different pages
>>     2.612 s/loop, 0.684 ms/page,  46765.812 MiB/s	2628 succeed, 1189 failed, 2628 different pages
>>     2.683 s/loop, 0.703 ms/page,  45520.990 MiB/s	2630 succeed, 1187 failed, 2630 different pages
>>     2.727 s/loop, 0.714 ms/page,  44789.321 MiB/s	2631 succeed, 1186 failed, 2631 different pages
>>     ...
>>   ok 1 Completed
>>
>> Suggested-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
>> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
>> ---
> 
> 
> [...]
> 
>> diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
>> index d09f9f6a384e..24aa1de27c25 100755
>> --- a/tools/testing/selftests/mm/run_vmtests.sh
>> +++ b/tools/testing/selftests/mm/run_vmtests.sh
>> @@ -360,8 +360,8 @@ fi
>>  CATEGORY="memfd_secret" run_test ./memfd_secret
>>  fi
>>  
>> -# KSM KSM_MERGE_TIME_HUGE_PAGES test with size of 100
>> -CATEGORY="ksm" run_test ./ksm_tests -H -s 100
>> +# KSM KSM_MERGE_TIME_HUGE_PAGES test with size of 512
>> +CATEGORY="ksm" run_test ./ksm_tests -H -s 512
> 
> 
> Why the magic value 512? (desrves a comment)
> 
> A clear sign that the ksm tests must be rewritten to be standalone and just
> handle this internally. @Sarthak

Sure David, I'll work on this.