selftests/mm: hugetlb_fault_after_madv: use default hugetlb page size

JIRA: https://issues.redhat.com/browse/RHEL-60023

commit 3b2faed
Author:     David Hildenbrand <david@redhat.com>
AuthorDate: Thu Sep 26 17:20:43 2024 +0200
Commit:     Andrew Morton <akpm@linux-foundation.org>
CommitDate: Tue Nov 5 16:56:25 2024 -0800

    selftests/mm: hugetlb_fault_after_madv: use default hugetlb page size

    Patch series "selftests/mm: hugetlb_fault_after_madv improvements".

    Mario brought to my attention that the hugetlb_fault_after_madv test is
    currently always skipped on s390x.  Let's adjust the test to be
    independent of the default hugetlb page size and while at it, also improve
    the test output.

    This patch (of 2):

    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.

    Link: https://lkml.kernel.org/r/20240926152044.2205129-1-david@redhat.com
    Link: https://lkml.kernel.org/r/20240926152044.2205129-2-david@redhat.com
    Signed-off-by: David Hildenbrand <david@redhat.com>
    Reported-by: Mario Casquero <mcasquer@redhat.com>
    Tested-by: Mario Casquero <mcasquer@redhat.com>
    Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
    Reviewed-by: Breno Leitao <leitao@debian.org>
    Cc: Shuah Khan <shuah@kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: David Hildenbrand <david@redhat.com>

Author: davidhildenbrand

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);
 
 	return NULL;
 }
@@ -47,14 +47,18 @@ int main(void)
 
 	srand(getpid());
 
+	huge_page_size = default_huge_page_size();
+	if (!huge_page_size)
+		ksft_exit_skip("Could not detect default hugetlb page size.");
+
 	free_hugepages = get_free_hugepages();
 	if (free_hugepages != 1) {
 		ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
 			       free_hugepages);
 	}
 
 	while (max--) {
-		huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
+		huge_ptr = mmap(NULL, huge_page_size, PROT_READ | PROT_WRITE,
 				MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
 				-1, 0);
 
@@ -66,7 +70,7 @@ int main(void)
 
 		pthread_join(thread1, NULL);
 		pthread_join(thread2, NULL);
-		munmap(huge_ptr, MMAP_SIZE);
+		munmap(huge_ptr, huge_page_size);
 	}
 
 	return KSFT_PASS;