linux-kernel - Re: [PATCH v3 6/9] selftests/mm: introduce helper to read every page

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Message-ID: <a4c83b16-3307-497d-9690-0e31672f3202@kernel.org>
Date: Thu, 22 Jan 2026 23:20:37 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Dev Jain <dev.jain@....com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Mark Brown <broonie@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v3 6/9] selftests/mm: introduce helper to read every page

On 1/22/26 18:02, Kevin Brodsky wrote:
> FORCE_READ(*addr) ensures that the compiler will emit a load from
> addr. Several tests need to trigger such a load for a range of
> pages, ensuring that every page is faulted in, if it wasn't already.
> 
> Introduce a new helper force_read_pages() that does exactly that and
> replace existing loops with a call to it.
> 
> The step size (regular/huge page size) is preserved for all loops,
> except in split_huge_page_test. Reading every byte is unnecessary;
> we now read every huge page, matching the following call to
> check_huge_file().
> 
> Reviewed-by: Dev Jain <dev.jain@....com>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
> ---
>   tools/testing/selftests/mm/hugetlb-madvise.c      | 9 +--------
>   tools/testing/selftests/mm/pfnmap.c               | 9 +++------
>   tools/testing/selftests/mm/split_huge_page_test.c | 6 +-----
>   tools/testing/selftests/mm/vm_util.h              | 7 +++++++
>   4 files changed, 12 insertions(+), 19 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/mm/hugetlb-madvise.c
> index 05d9d2805ae4..5b12041fa310 100644
> --- a/tools/testing/selftests/mm/hugetlb-madvise.c
> +++ b/tools/testing/selftests/mm/hugetlb-madvise.c
> @@ -47,14 +47,7 @@ void write_fault_pages(void *addr, unsigned long nr_pages)
>   
>   void read_fault_pages(void *addr, unsigned long nr_pages)
>   {
> -	unsigned long i;
> -
> -	for (i = 0; i < nr_pages; i++) {
> -		unsigned long *addr2 =
> -			((unsigned long *)(addr + (i * huge_page_size)));
> -		/* Prevent the compiler from optimizing out the entire loop: */
> -		FORCE_READ(*addr2);
> -	}
> +	force_read_pages(addr, nr_pages, huge_page_size);
>   }

Likely we could get rid of read_fault_pages() completely and simply let 
the callers call force_read_pages() now?

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>


-- 
Cheers

David