Re: [PATCH v6 2/3] kselftest: mm: remove HPAGE_SIZE and HPAGE_SHIFT macro

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

On Tue, Oct 13, 2026 at 03:26:40PM +0530, Sarthak Sharma wrote:
> Hi Yeoreum!
> 
> On 10/13/26 3:16 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 macro and introduce pmd_pshift()
> > helper to get the HPAGE_SHIFT properly. For HPAGE_SIZE, use pre-existing
> > helper, pmd_psize().
> > 
> > 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>
> > Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
> > Reviewed-by: Zi Yan <ziy@nvidia.com>
> > Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> 
> [...]
> 
> > diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> > index 5f2fb5b819c4a..efd99298be135 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_psize = -1ull;
> > +uint64_t __pmd_pshift = -1ull;
> >  
> >  uint64_t pagemap_get_entry(int fd, char *start)
> >  {
> > @@ -161,19 +163,40 @@ uint64_t pmd_psize(void)
> >  	char buf[20];
> >  	ssize_t num_read;
> >  
> > +	if (__pmd_psize != -1ull)
> > +		return __pmd_psize;
> > +
> >  	fd = open(PMD_SIZE_FILE_PATH, O_RDONLY);
> > -	if (fd == -1)
> > +	if (fd == -1) {
> > +		__pmd_psize = 0;
> >  		return 0;
> > +	}
> >  
> >  	num_read = read(fd, buf, 19);
> >  	if (num_read < 1) {
> > +		__pmd_psize = 0;
> >  		close(fd);
> >  		return 0;
> >  	}
> >  	buf[num_read] = '\0';
> >  	close(fd);
> >  
> > -	return strtoul(buf, NULL, 10);
> > +	__pmd_psize = strtoul(buf, NULL, 10);
> > +
> > +	return __pmd_psize;
> > +}
> > +
> > +uint64_t pmd_pshift(void)
> > +{
> > +	if (__pmd_pshift != -1ull)
> > +		return __pmd_pshift;
> > +
> > +	if (__pmd_psize != -1ull)
> > +		__pmd_psize = pmd_psize();
> 
> Kiryl pointed this out in v5 [1], you might have missed it. This check
> seems to be inverted.
> 
> [1] https://lore.kernel.org/all/asj4dT2Q__SlKhgr@thinkstation/

Oh. Thanks. I've missed. 

-- 
Sincerely,
Yeoreum Yun