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

[Yeoreum Yun <yeoreum.yun@arm.com>]

> > On Wed, Sep 02, 2026 at 06:56:11PM +0100, 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 than 4KB.
> > >
> > > Here is 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 macro. and introduce hpshift()
> > > helper to get the HPAGE_SHIFT properly. For HPAGE_SIZE, use pre-exist
> > > helper, read_pmd_pagesize().
> > >
> > > Also, do KSM_MERGE_TIME_HUGE_PAGES test with size of 512 MiB which
> > > is the LCD pmd_size among 4KB, 16KB and 64KB page_size.
> > 
> > Probably worth spelling out Least Common Denominator for those who might
> > mistaken this for a kind of display panel :P
> 
> Bad typo :( LCM (least common multiple) :(
> 
> > 
> > I also wonder if it's worth pulling that out as a separate patch in a series for
> > better bisectability?
> 
> Okay. I'll separate it.

Hmm, I think it would be better to keep the change as is, including the
updated ksm_tests parameter. Although allocate_transhuge() correctly
allocates mappings aligned to the PMD page size, `ksm_tests -H -s 100`
would otherwise fail because 100 MiB is not a multiple of the PMD page
size.

[...]

-- 
Sincerely,
Yeoreum Yun