linux-kernel - Re: [PATCH v3 4/7] mm/selftests: Fix split_huge_page_test failure on systems with 64KB page size

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Message-ID: <65660d5f-a856-4244-8a81-1359a03f16be@redhat.com>
Date: Mon, 4 Aug 2025 16:33:52 +0200
From: David Hildenbrand <david@...hat.com>
To: Wei Yang <richard.weiyang@...il.com>,
 Aboorva Devarajan <aboorvad@...ux.ibm.com>
Cc: akpm@...ux-foundation.org, Liam.Howlett@...cle.com,
 lorenzo.stoakes@...cle.com, shuah@...nel.org, pfalcato@...e.de,
 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 v3 4/7] mm/selftests: Fix split_huge_page_test failure on
 systems with 64KB page size

On 04.08.25 11:04, Wei Yang wrote:
> On Tue, Jul 29, 2025 at 11:04:00AM +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")
>> Reviewed-by: Dev Jain <dev.jain@....com>
>> Reviewed-by: Zi Yan <ziy@...dia.com>
>> Co-developed-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
>> Signed-off-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
>> Signed-off-by: Donet Tom <donettom@...ux.ibm.com>
>> ---
>> .../selftests/mm/split_huge_page_test.c       | 23 ++++++++++++-------
>> 1 file changed, 15 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index 05de1fc0005b..718daceb5282 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -36,6 +36,7 @@ uint64_t pmd_pagesize;
>>
>> #define PFN_MASK     ((1UL<<55)-1)
>> #define KPF_THP      (1UL<<22)
>> +#define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))
>>
>> int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>> {
>> @@ -522,6 +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();
>>
>> @@ -533,35 +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 = GET_ORDER(nr_pages);
> 
> There is a sz2ord() in cow.c and uffd-wp-mremap.c.
> 
> Maybe we can factor it into vm_util.h and use it here.

That sounds reasonable to me.

-- 
Cheers,

David / dhildenb