Re: [PATCH v7 2/3] kselftest: mm: remove HPAGE_SIZE and HPAGE_SHIFT macro

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

> Hi Yeoreum!
> 
> On 10/13/26 4:07 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>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> >  tools/testing/selftests/mm/guard-regions.c    | 10 +++++--
> >  tools/testing/selftests/mm/ksm_tests.c        | 16 ++++++-----
> >  tools/testing/selftests/mm/run_vmtests.sh     |  4 +--
> >  tools/testing/selftests/mm/transhuge-stress.c | 25 +++++++++++-------
> >  tools/testing/selftests/mm/vm_util.c          | 38 +++++++++++++++++++++++----
> >  tools/testing/selftests/mm/vm_util.h          |  9 +++----
> >  6 files changed, 71 insertions(+), 31 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c
> > index f7d53ea3c2527..02f69244f9a42 100644
> > --- a/tools/testing/selftests/mm/guard-regions.c
> > +++ b/tools/testing/selftests/mm/guard-regions.c
> > @@ -2194,14 +2194,20 @@ TEST_F(guard_regions, pagemap_scan)
> >  TEST_F(guard_regions, collapse)
> >  {
> >  	const unsigned long page_size = self->page_size;
> > -	const unsigned long size = 2 * HPAGE_SIZE;
> > -	const unsigned long num_pages = size / page_size;
> > +	const uint64_t hpage_size = pmd_psize();
> > +	unsigned long size, num_pages;
> >  	char *ptr;
> >  	int i;
> >  
> >  	if (!thp_available())
> >  		SKIP(return, "Transparent Hugepages not available\n");
> >  
> > +	if (!hpage_size)
> > +		ksft_exit_fail_msg("reading hpage_size failed\n");
> 
> I'm sorry for not catching this earlier, but I don't think calling a
> ksft_exit_fail_msg() for not being able to calculate PMD size is a good
> idea. Maybe call an ASSERT*() here, something like
> 
> ASSERT_NE(hpage_size, 0);
> 
> so that just this test fails, instead of the whole run exiting with a
> bail out?

No. The failure would occur if open() or read() fails, and subsequent
attempts would likely fail for the same reason.
This is also why __pmd_size is set to 0 after a failed attempt.

We don't need to produce useless failure log anymore.

[...snip...]


-- 
Sincerely,
Yeoreum Yun