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

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

On Tue, Sep 08, 2026 at 12:21:31PM +0200, David Hildenbrand (Arm) wrote:
> On 9/8/26 10:23, Yeoreum Yun wrote:
> > On Mon, Sep 07, 2026 at 04:36:56PM +0200, 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
> > 
> > Acked. I thought it's enough to spell out in commit message but
> > I'll spell out into comment too in this round not refactorying by me
> > for ksm test.
> > 
> >>
> >>>  # KSM KSM_MERGE_TIME test with size of 100
> >>>  CATEGORY="ksm" run_test ./ksm_tests -P -s 100
> >>>  # KSM MADV_MERGEABLE test with 10 identical pages
> >>
> >> [...]
> >>
> >>> index 4821a3563036..f75bf0bacd18 100644
> >>> --- a/tools/testing/selftests/mm/vm_util.c
> >>> +++ b/tools/testing/selftests/mm/vm_util.c
> >>> @@ -21,6 +21,8 @@
> >>>  
> >>>  unsigned int __page_size;
> >>>  unsigned int __page_shift;
> >>> +uint64_t __pmd_page_size;
> >>> +uint64_t __pmd_page_shift;
> >>>  
> >>>  uint64_t pagemap_get_entry(int fd, char *start)
> >>>  {
> >>> @@ -161,6 +163,9 @@ uint64_t read_pmd_pagesize(void)
> >>>  	char buf[20];
> >>>  	ssize_t num_read;
> >>>  
> >>> +	if (__pmd_page_size)
> >>> +		return __pmd_page_size;
> >>> +
> >>>  	fd = open(PMD_SIZE_FILE_PATH, O_RDONLY);
> >>>  	if (fd == -1)
> >>>  		return 0;
> >>> @@ -173,7 +178,25 @@ uint64_t read_pmd_pagesize(void)
> >>>  	buf[num_read] = '\0';
> >>>  	close(fd);
> >>>  
> >>> -	return strtoul(buf, NULL, 10);
> >>> +	__pmd_page_size = strtoul(buf, NULL, 10);
> >>> +
> >>> +	return __pmd_page_size;
> >>> +}
> >>> +
> >>> +uint64_t pmd_page_shift(void)
> >>> +{
> >>> +	if (__pmd_page_shift)
> >>> +		return __pmd_page_shift;
> >>> +
> >>> +	if (!__pmd_page_size)
> >>> +		__pmd_page_size = read_pmd_pagesize();
> >>> +
> >>> +	if (!__pmd_page_size)
> >>> +		return 0;
> >>> +
> >>> +	__pmd_page_shift = (ffsl(__pmd_page_size) - 1);
> >>> +
> >>> +	return __pmd_page_shift;
> >>>  }
> >> The interface is a bit inconsistent.
> >>
> >> read_pmd_pagesize() vs. pmd_page_shift().
> >>
> >> Consider renaming read_pmd_pagesize() to pmd_pagesize() in a cleanup patch.
> > 
> > Okay.
> > 
> >> ... or (better?) adding a size_to_shift() helper instead?
> >>
> >> I think most places that want the shift also want the size.
> >>
> >> So this can just be
> >>
> >> const uint64_t hpage_size = read_pmd_pagesize();
> >> const uint64_t hpage_shift = size_to_shift(hpage_size);
> >>
> >>
> >> In size_to_shift(), you can just handle
> >>
> >> if (size == 0)
> >> 	return 0;
> > 
> > Hmm, most of tests care mainly two sizes and shiftes --
> > psize()/pshift() and pmd_pagesize() and pmd_pageshift().
> > 
> > Would it be better to keep both kinda of helpers and
> > add size_to_shift() helper for nother hpage size then?
> 
> Works for me as well. As long as it's consistent.
> 
> Maybe even pmd_psize() and pmd_pshift() to match our custom psize() and pshift()?

Yeap. That would be better. I'll repsin soon.

-- 
Sincerely,
Yeoreum Yun