linux-kernel - Re: [PATCH 1/2] selftests: mincore: fix tmpfs mincore test failure

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Message-ID: <9000c5c1-34be-4bc9-b1c0-11548264eaa6@redhat.com>
Date: Tue, 1 Apr 2025 14:54:47 +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 1/2] selftests: mincore: fix tmpfs mincore test failure

On 26.03.25 04:38, 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.
> 
> To fix this issue, remount tmpfs to a new test directory and set the 'huge=never'
> parameter to avoid allocating large folios, which can pass the test.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>   .../selftests/mincore/mincore_selftest.c      | 25 +++++++++++++++++--
>   1 file changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/mincore/mincore_selftest.c b/tools/testing/selftests/mincore/mincore_selftest.c
> index e949a43a6145..e8d7a3a4739f 100644
> --- a/tools/testing/selftests/mincore/mincore_selftest.c
> +++ b/tools/testing/selftests/mincore/mincore_selftest.c
> @@ -12,6 +12,7 @@
>   #include <unistd.h>
>   #include <stdlib.h>
>   #include <sys/mman.h>
> +#include <sys/mount.h>
>   #include <string.h>
>   #include <fcntl.h>
>   
> @@ -283,7 +284,7 @@ TEST(check_file_mmap)
>   	free(vec);
>   }
>   
> -
> +#define INPUT_MAX 80
>   /*
>    * 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
> @@ -291,6 +292,9 @@ TEST(check_file_mmap)
>    */
>   TEST(check_tmpfs_mmap)
>   {
> +	char tmpfs_template[] = "/tmp/check_tmpfs_XXXXXX";
> +	const char *tmpfs_loc = mkdtemp(tmpfs_template);
> +	char testfile[INPUT_MAX];
>   	unsigned char *vec;
>   	int vec_size;
>   	char *addr;
> @@ -300,6 +304,10 @@ TEST(check_tmpfs_mmap)
>   	int i;
>   	int ra_pages = 0;
>   
> +	ASSERT_NE(NULL, tmpfs_loc) {
> +		TH_LOG("Can't mkdir tmpfs dentry\n");
> +	}
> +
>   	page_size = sysconf(_SC_PAGESIZE);
>   	vec_size = FILE_SIZE / page_size;
>   	if (FILE_SIZE % page_size)
> @@ -311,7 +319,18 @@ TEST(check_tmpfs_mmap)
>   	}
>   
>   	errno = 0;
> -	fd = open("/dev/shm", O_TMPFILE | O_RDWR, 0600);
> +	/* Do not use large folios for tmpfs mincore testing */
> +	retval = mount("tmpfs", tmpfs_loc, "tmpfs", 0, "huge=never,size=4M");
> +	ASSERT_EQ(0, retval) {
> +		TH_LOG("Unable to mount tmpfs for testing\n");
> +	}
> +
> +	retval = snprintf(testfile, INPUT_MAX, "%s/test_file", tmpfs_loc);
> +	ASSERT_GE(INPUT_MAX, retval) {
> +		TH_LOG("Unable to create a tmpfs for testing\n");
> +	}
> +
> +	fd = open(testfile, O_CREAT|O_RDWR, 0664);
>   	ASSERT_NE(-1, fd) {
>   		TH_LOG("Can't create temporary file: %s",
>   			strerror(errno));
> @@ -363,6 +382,8 @@ TEST(check_tmpfs_mmap)
>   	munmap(addr, FILE_SIZE);
>   	close(fd);
>   	free(vec);
> +	umount(tmpfs_loc);
> +	rmdir(tmpfs_loc);
>   }
>   
>   TEST_HARNESS_MAIN

Is there anything that cleans up the mount in case something goes wrong 
(we run into an assertion), or will the directory+mount stick around 
forever?

But I also wonder whether check_tmpfs_mmap() should be changed to live 
with the fact that readahead ("faultaround") could now happen. What's 
the reason for not doing that?

-- 
Cheers,

David / dhildenb