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

[David Hildenbrand]

On 07.04.25 05:49, Baolin Wang wrote:
> 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@xxxxxxxxxxxxxxxxx>
> > > ---
> > >    .../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.

Yes, but why are we testing for that *at all*? We don't make such 
assumptions/tests for anon memmory ("no faultaround happened").

Why not simply remove the "We expect only that page to be fetched into 
memory." documentation + checking?

--
Cheers,

David / dhildenb