linux-kernel - Re: [PATCH v2] selftests: mincore: fix tmpfs mincore test failure

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Message-ID: <61e36a73-2c8c-4897-9ba5-3b2d59f57b5d@redhat.com>
Date: Mon, 7 Apr 2025 17:04:42 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 hughd@...gle.com
Cc: willy@...radead.org, 21cnbao@...il.com, ryan.roberts@....com,
 ziy@...dia.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] selftests: mincore: fix tmpfs mincore test failure

On 07.04.25 13:31, Baolin Wang wrote:
> When running mincore test cases, I encountered the following failures:
> 
> "
> mincore_selftest.c:359:check_tmpfs_mmap:Expected ra_pages (511) == 0 (0)
> mincore_selftest.c:360:check_tmpfs_mmap:Read-ahead pages found in memory
> check_tmpfs_mmap: Test terminated by assertion
>            FAIL  global.check_tmpfs_mmap
> not ok 5 global.check_tmpfs_mmap
> FAILED: 4 / 5 tests passed
> "
> 
> The reason for the test case failure is that my system automatically enabled
> tmpfs large folio allocation by adding the 'transparent_hugepage_tmpfs=always'
> cmdline. However, the test case still expects the tmpfs mounted on /dev/shm to
> allocate small folios, which leads to assertion failures when verifying readahead
> pages.
> 
> As discussed with David, there's no reason to continue checking the readahead
> logic for tmpfs. Drop it to fix this issue.
> 

BTW, should we add a Fixes: ? Could only be tmpfs support that changed 
the behavior but didn't fixup the test case.

> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> Changes from v1:
>   - Drop the readahead logic check, per David.
> ---
>   .../testing/selftests/mincore/mincore_selftest.c | 16 ++--------------
>   1 file changed, 2 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/testing/selftests/mincore/mincore_selftest.c b/tools/testing/selftests/mincore/mincore_selftest.c
> index e949a43a6145..0fd4b00bd345 100644
> --- a/tools/testing/selftests/mincore/mincore_selftest.c
> +++ b/tools/testing/selftests/mincore/mincore_selftest.c
> @@ -286,8 +286,7 @@ TEST(check_file_mmap)
>   
>   /*
>    * Test mincore() behavior on a page backed by a tmpfs file.  This test
> - * performs the same steps as the previous one. However, we don't expect
> - * any readahead in this case.
> + * performs the same steps as the previous one.
>    */
>   TEST(check_tmpfs_mmap)
>   {
> @@ -298,7 +297,6 @@ TEST(check_tmpfs_mmap)
>   	int page_size;
>   	int fd;
>   	int i;
> -	int ra_pages = 0;
>   
>   	page_size = sysconf(_SC_PAGESIZE);
>   	vec_size = FILE_SIZE / page_size;
> @@ -341,8 +339,7 @@ TEST(check_tmpfs_mmap)
>   	}
>   
>   	/*
> -	 * Touch a page in the middle of the mapping. We expect only
> -	 * that page to be fetched into memory.
> +	 * Touch a page in the middle of the mapping.
>   	 */
>   	addr[FILE_SIZE / 2] = 1;
>   	retval = mincore(addr, FILE_SIZE, vec);
> @@ -351,15 +348,6 @@ TEST(check_tmpfs_mmap)
>   		TH_LOG("Page not found in memory after use");
>   	}
>   
> -	i = FILE_SIZE / 2 / page_size + 1;
> -	while (i < vec_size && vec[i]) {
> -		ra_pages++;
> -		i++;
> -	}
> -	ASSERT_EQ(ra_pages, 0) {
> -		TH_LOG("Read-ahead pages found in memory");
> -	}
> -
>   	munmap(addr, FILE_SIZE);
>   	close(fd);
>   	free(vec);

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb