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

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Message-ID: <cefb4920-36ad-404f-b058-f50eea52c418@linux.alibaba.com>
Date: Mon, 7 Apr 2025 11:49:05 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.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 2025/4/1 20:54, David Hildenbrand wrote:
> 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?

Good point, will cleanup the mount in the next version.

> 
> 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?

 From this test case's description, it doesn't expect any readahead.
"
/*
  * 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.
  */
"

Maybe adding a new test case to expect the readahead for tmpfs file.