linux-kernel - Re: [PATCH v4 4/7] mm/selftests: Fix split_huge_page_test failure on systems with 64KB page size

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Message-ID: <588d7bc1af412052da01ada1e316dc3452e35435.camel@linux.ibm.com>
Date: Tue, 19 Aug 2025 13:27:19 +0530
From: Aboorva Devarajan <aboorvad@...ux.ibm.com>
To: Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, shuah@...nel.org,
        pfalcato@...e.de, david@...hat.com, ziy@...dia.com,
        baolin.wang@...ux.alibaba.com, npache@...hat.com, ryan.roberts@....com,
        dev.jain@....com, baohua@...nel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        donettom@...ux.ibm.com, ritesh.list@...il.com
Subject: Re: [PATCH v4 4/7] mm/selftests: Fix split_huge_page_test failure
 on systems with 64KB page size

On Sat, 2025-08-16 at 14:31 +0000, Wei Yang wrote:
> On Sat, Aug 16, 2025 at 09:31:10AM +0530, Aboorva Devarajan wrote:
> > From: Donet Tom <donettom@...ux.ibm.com>
> > 
> > The split_huge_page_test fails on systems with a 64KB base page
> > size.
> > This is because the order of a 2MB huge page is different:
> > 
> > On 64KB systems, the order is 5.
> > 
> > On 4KB systems, it's 9.
> > 
> > The test currently assumes a maximum huge page order of 9, which is
> > only
> > valid for 4KB base page systems. On systems with 64KB pages,
> > attempting
> > to split huge pages beyond their actual order (5) causes the test
> > to fail.
> > 
> > In this patch, we calculate the huge page order based on the
> > system's base
> > page size. With this change, the tests now run successfully on both
> > 64KB
> > and 4KB page size systems.
> > 
> > Fixes: fa6c02315f745 ("mm: huge_memory: a new debugfs interface for
> > splitting THP tests")
> > Co-developed-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
> > Signed-off-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
> > Reviewed-by: Dev Jain <dev.jain@....com>
> > Reviewed-by: Zi Yan <ziy@...dia.com>
> > Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
> 
> Reviewed-by: Wei Yang <richard.weiyang@...il.com>
> 
> Nit below:
> 
> > ---
> > tools/testing/selftests/mm/cow.c              |  5 -----
> > .../selftests/mm/split_huge_page_test.c       | 22 ++++++++++++----
> > ---
> > tools/testing/selftests/mm/uffd-wp-mremap.c   |  5 -----
> > tools/testing/selftests/mm/vm_util.h          |  5 +++++
> > 4 files changed, 19 insertions(+), 18 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/mm/cow.c
> > b/tools/testing/selftests/mm/cow.c
> > index 90ee5779662f..e742d9313798 100644
> > --- a/tools/testing/selftests/mm/cow.c
> > +++ b/tools/testing/selftests/mm/cow.c
> > @@ -41,11 +41,6 @@ static size_t hugetlbsizes[10];
> > static int gup_fd;
> > static bool has_huge_zeropage;
> > 
> > -static int sz2ord(size_t size)
> > -{
> > -	return __builtin_ctzll(size / pagesize);
> > -}
> > -
> > static int detect_thp_sizes(size_t sizes[], int max)
> > {
> > 	int count = 0;
> > diff --git a/tools/testing/selftests/mm/split_huge_page_test.c
> > b/tools/testing/selftests/mm/split_huge_page_test.c
> > index eadbeb820d71..7cbeaebc9d71 100644
> > --- a/tools/testing/selftests/mm/split_huge_page_test.c
> > +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> > @@ -523,6 +523,9 @@ int main(int argc, char **argv)
> > 	const char *fs_loc;
> > 	bool created_tmp;
> > 	int offset;
> > +	unsigned int max_order;
> > +	unsigned int nr_pages;
> > +	unsigned int tests;
> > 
> > 	ksft_print_header();
> > 
> > @@ -534,35 +537,38 @@ int main(int argc, char **argv)
> > 	if (argc > 1)
> > 		optional_xfs_path = argv[1];
> > 
> > -	ksft_set_plan(1+8+1+9+9+8*4+2);
> > -
> > 	pagesize = getpagesize();
> > 	pageshift = ffs(pagesize) - 1;
> > 	pmd_pagesize = read_pmd_pagesize();
> > 	if (!pmd_pagesize)
> > 		ksft_exit_fail_msg("Reading PMD pagesize
> > failed\n");
> > 
> > +	nr_pages = pmd_pagesize / pagesize;
> > +	max_order =  sz2ord(pmd_pagesize);
>                     ^
> 		    extra space here

Hi Wei,

Thanks for the review. I’ve sent a fixup patch for this:
https://lore.kernel.org/all/20250819041239.167537-1-aboorvad@linux.ibm.com/

Andrew, 

Could you please apply the above fixup patch?

Regards,
Aboorva

> 
> > +	tests = 2 + (max_order - 1) + (2 * max_order) + (max_order
> > - 1) * 4 + 2;
> > +	ksft_set_plan(tests);
> > +
> > 	fd_size = 2 * pmd_pagesize;
> > 
> > 	split_pmd_zero_pages();
> >