linux-kernel - Re: [PATCH v5 3/5] selftests/mm: reimplement is_backed_by

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Message-ID: <268d9c9b-4c48-449c-97c7-33534fb23fa3@redhat.com>
Date: Tue, 19 Aug 2025 10:54:31 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, Wei Yang <richard.weiyang@...il.com>,
 wang lian <lianux.mm@...il.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.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>, Vlastimil Babka <vbabka@...e.cz>,
 Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Shuah Khan <shuah@...nel.org>,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 3/5] selftests/mm: reimplement is_backed_by_thp() with
 more precise check

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@...dia.com>
> Reviewed-by: Wei Yang <richard.weiyang@...il.com>
> Reviewed-by: wang lian <lianux.mm@...il.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@...hat.com>

-- 
Cheers

David / dhildenb