Re: [PATCH v5 3/5] selftests/mm: reimplement is_backed_by_thp() with more precise check

[David Hildenbrand <david@redhat.com>]

On 18.08.25 20:46, Zi Yan wrote:
> and rename it to is_backed_by_folio().
> 
> is_backed_by_folio() checks if the given vaddr is backed a folio with
> a given order. It does so by:
> 1. getting the pfn of the vaddr;
> 2. checking kpageflags of the pfn;
> 
> if order is greater than 0:
> 3. checking kpageflags of the head pfn;
> 4. checking kpageflags of all tail pfns.
> 
> pmd_order is added to split_huge_page_test.c and replaces max_order.
> 
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
> Reviewed-by: wang lian <lianux.mm@gmail.com>
> ---
>   .../selftests/mm/split_huge_page_test.c       | 88 ++++++++++++++-----
>   tools/testing/selftests/mm/vm_util.c          | 13 +++
>   tools/testing/selftests/mm/vm_util.h          |  4 +
>   3 files changed, 81 insertions(+), 24 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index 089e146efeab..56d1eaf9a860 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -25,6 +25,7 @@
>   uint64_t pagesize;
>   unsigned int pageshift;
>   uint64_t pmd_pagesize;
> +unsigned int pmd_order;
>   
>   #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
>   #define SMAP_PATH "/proc/self/smaps"
> @@ -34,26 +35,66 @@ uint64_t pmd_pagesize;
>   #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)
> -#define KPF_THP      (1UL<<22)
> -
> -static int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
> +static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
> +		int kpageflags_fd)
>   {
> -	uint64_t paddr;
> -	uint64_t page_flags;
> +	unsigned long pfn_head;
> +	uint64_t pfn_flags;
> +	unsigned long pfn;
> +	unsigned long i;

Final nit (sorry!) :)

const unsigned long nr_pages = 1ul << order;

so you can make some of the code below easier to read.

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

-- 
Cheers

David / dhildenb