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

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

Hi Yeoreum!

On 9/7/26 1:45 PM, 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>
> ---
> Chnage in v2:
>  - rename hpage_* to pmd_page_*
>  - Link to v1: https://lore.kernel.org/all/20260902175611.1241118-1-yeoreum.yun@arm.com/#t
Thanks for accepting the suggestion to rename :)

I've tested this patch on 16kB and 64kB machines. Before the patch,
transhuge_stress attempted the same number of allocations irrespective
of the page size, since HPAGE_SIZE was hardcoded. After applying the
patch, it correctly reads PMD size and calculates the attempts accordingly.

Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
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