linux-kernel - Re: [PATCH] selftests/mm: fix split_huge_page_test for folio

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Message-ID: <F9C3F0B9-7A83-4CE5-945E-6BBC3F16B149@nvidia.com>
Date: Fri, 11 Jul 2025 10:19:01 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Shuah Khan <shuah@...nel.org>,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/mm: fix split_huge_page_test for folio_split()
 tests.

On 11 Jul 2025, at 9:29, David Hildenbrand wrote:

> On 09.07.25 03:27, Zi Yan wrote:
>> PID_FMT does not have an offset field, so folio_split() tests are not
>> performed. Add PID_FMT_OFFSET with an offset field and use it to perform
>> folio_split() tests.
>>
>> Fixes: 80a5c494c89f ("selftests/mm: add tests for folio_split(), buddy allocator like split")
>> Signed-off-by: Zi Yan <ziy@...dia.com>
>> ---
>>   tools/testing/selftests/mm/split_huge_page_test.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>> index aa7400ed0e99..f0d9c035641d 100644
>> --- a/tools/testing/selftests/mm/split_huge_page_test.c
>> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
>> @@ -31,6 +31,7 @@ uint64_t pmd_pagesize;
>>   #define INPUT_MAX 80
>>    #define PID_FMT "%d,0x%lx,0x%lx,%d"
>> +#define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
>>   #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>>    #define PFN_MASK     ((1UL<<55)-1)
>> @@ -483,7 +484,7 @@ void split_thp_in_pagecache_to_order_at(size_t fd_size, const char *fs_loc,
>>   		write_debugfs(PID_FMT, getpid(), (uint64_t)addr,
>>   			      (uint64_t)addr + fd_size, order);
>>   	else
>> -		write_debugfs(PID_FMT, getpid(), (uint64_t)addr,
>> +		write_debugfs(PID_FMT_OFFSET, getpid(), (uint64_t)addr,
>>   			      (uint64_t)addr + fd_size, order, offset);
>>    	for (i = 0; i < fd_size; i++)
>
> So I assume the tests still passed. Would there be a way to have made them fail? (IOW, detect that the wrong kind-of split was performed)

Only if the initial PMD page is not split. To detect whether all after-split
folios are the size we expect, additional code that reads kpageflags
is needed. I will put it in my TODO to make this test more robust.

>
> Acked-by: David Hildenbrand <david@...hat.com>

Thanks.

Best Regards,
Yan, Zi