linux-kernel - Re: [PATCH v1 1/2] selftests/mm: hugetlb_fault_after

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Message-ID: <5d9c8052-e7ca-4819-bd0c-d7f88905c7a1@linuxfoundation.org>
Date: Thu, 26 Sep 2024 10:03:50 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>,
 Mario Casquero <mcasquer@...hat.com>, Breno Leitao <leitao@...ian.org>,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v1 1/2] selftests/mm: hugetlb_fault_after_madv: use
 default hguetlb page size

On 9/26/24 09:20, David Hildenbrand wrote:
> We currently assume that the hugetlb page size is 2 MiB, which is
> why we mmap() a 2 MiB range.
> 
> Is the default hugetlb size is larger, mmap() will fail because the
> range is not suitable. If the default hugetlb size is smaller (e.g.,
> s390x), mmap() will fail because we would need more than one hugetlb
> page, but just asserted that we have exactly one.
> 
> So let's simply use the default hugetlb page size instead of hard-coded
> 2 MiB, so the test isn't unconditionally skipped on architectures like
> s390x.
> 
> Before this patch on s390x:
> $ ./hugetlb_fault_after_madv
> 	1..0 # SKIP Failed to allocated huge page
> 
> With this change on s390x:
> 	$ ./hugetlb_fault_after_madv
> 
> While at it, make "huge_ptr" static.
> 
> Reported-by: Mario Casquero <mcasquer@...hat.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>   .../selftests/mm/hugetlb_fault_after_madv.c        | 14 +++++++++-----
>   1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> index 73b81c632366..ff3ba675278d 100644
> --- a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> +++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
> @@ -9,10 +9,10 @@
>   #include "vm_util.h"
>   #include "../kselftest.h"
>   
> -#define MMAP_SIZE (1 << 21)
>   #define INLOOP_ITER 100
>   
> -char *huge_ptr;
> +static char *huge_ptr;
> +static size_t huge_page_size;
>   
>   /* Touch the memory while it is being madvised() */
>   void *touch(void *unused)
> @@ -30,7 +30,7 @@ void *madv(void *unused)
>   	usleep(rand() % 10);
>   
>   	for (int i = 0; i < INLOOP_ITER; i++)
> -		madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
> +		madvise(huge_ptr, huge_page_size, MADV_DONTNEED);

Magical effects of hard-coded values :)

Thank you for fixing this

Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>

thanks,
-- Shuah