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Date: Fri, 29 Aug 2025 20:09:53 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Wei Yang <richard.weiyang@gmail.com>
Cc: david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com,
 baolin.wang@linux.alibaba.com, linux-mm@kvack.org,
 linux-kselftest@vger.kernel.org
Subject: Re: [PATCH] selftests/mm: directly add pagesize instead of increase
 until page size
Message-Id: <20250829200953.1757e85542b1126c4881d600@linux-foundation.org>
In-Reply-To: <20250830023102.14981-1-richard.weiyang@gmail.com>
References: <20250830023102.14981-1-richard.weiyang@gmail.com>
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On Sat, 30 Aug 2025 02:31:02 +0000 Wei Yang <richard.weiyang@gmail.com> wrote:

> The check of is_backed_by_folio() is done on each page.
> 
> Directly move pointer to next page instead of increase one and check if
> it is page size aligned.

Why?

> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -423,9 +423,8 @@ static void split_pte_mapped_thp(void)
>  
>  	/* smap does not show THPs after mremap, use kpageflags instead */
>  	thp_size = 0;
> -	for (i = 0; i < pagesize * 4; i++)
> -		if (i % pagesize == 0 &&
> -		    is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
> +	for (i = 0; i < pagesize * 4; i += pagesize)
> +		if (is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd))
>  			thp_size++;

Looks like we're doing more work.  Is there something wrong with the
existing code?