linux-kernel - Re: [PATCH 10/29] selftests/mm: Test UFFDIO

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Date:   Fri, 31 Mar 2023 11:37:26 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Leonardo Bras Soares Passos <lsoaresp@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH 10/29] selftests/mm: Test UFFDIO_ZEROPAGE only when
 !hugetlb

On 03/30/23 12:07, Peter Xu wrote:
> Make the check as simple as "test_type == TEST_HUGETLB" because that's the
> only mem that doesn't support ZEROPAGE.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  tools/testing/selftests/mm/userfaultfd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/userfaultfd.c b/tools/testing/selftests/mm/userfaultfd.c
> index 795fbc4d84f8..d724f1c78847 100644
> --- a/tools/testing/selftests/mm/userfaultfd.c
> +++ b/tools/testing/selftests/mm/userfaultfd.c
> @@ -1118,7 +1118,7 @@ static int __uffdio_zeropage(int ufd, unsigned long offset, bool retry)
>  {
>  	struct uffdio_zeropage uffdio_zeropage;
>  	int ret;
> -	bool has_zeropage = get_expected_ioctls(0) & (1 << _UFFDIO_ZEROPAGE);
> +	bool has_zeropage = !(test_type == TEST_HUGETLB);

It is true that hugetlb is the only mem type that does not support zeropage.
So, the change is correct.

However, I actually prefer the explicit check that is there today.  It seems
more like a test of the API.  And, is more future proof is code changes.

Just my opinion/thoughts, not a strong objection.
-- 
Mike Kravetz