[PATCH v2 5/8] selftests/mm: introduce helper to read every page in range

Kevin Brodsky
2026-01-07T16:49:05Z

FORCE_READ(*addr) ensures that the compiler will emit a load from
addr. Several tests need to trigger such a load for every page in
the range [addr, addr + len), ensuring that every page is faulted
in, if it wasn't already.

Introduce a new helper force_read_pages_in_range() that does exactly
that and replace existing loops with a call to it. Some of those
loops have a different step size, but reading from every page is
appropriate in all cases.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
tools/testing/selftests/mm/hugetlb-madvise.c | 9 +--------
tools/testing/selftests/mm/pfnmap.c | 16 ++++++----------
.../testing/selftests/mm/split_huge_page_test.c | 6 +-----
tools/testing/selftests/mm/vm_util.h | 6 ++++++
4 files changed, 14 insertions(+), 23 deletions(-)

diff --git a/tools/testing/selftests/mm/hugetlb-madvise.c b/tools/testing/selftests/mm/hugetlb-madvise.c
index 05d9d2805ae4..1f82568ae262 100644
--- a/tools/testing/selftests/mm/hugetlb-madvise.c
+++ b/tools/testing/selftests/mm/hugetlb-madvise.c
@@ -47,14 +47,7 @@ void write_fault_pages(void *addr, unsigned long nr_pages)

void read_fault_pages(void *addr, unsigned long nr_pages)
{
- unsigned long i;
-
- for (i = 0; i < nr_pages; i++) {
- unsigned long *addr2 =
- ((unsigned long *)(addr + (i * huge_page_size)));
- /* Prevent the compiler from optimizing out the entire loop: */
- FORCE_READ(*addr2);
- }
+ force_read_pages_in_range(addr, nr_pages * huge_page_size);
}

int main(int argc, char **argv)
diff --git a/tools/testing/selftests/mm/pfnmap.c b/tools/testing/selftests/mm/pfnmap.c
index f546dfb10cae..35b0e3ed54cd 100644
--- a/tools/testing/selftests/mm/pfnmap.c
+++ b/tools/testing/selftests/mm/pfnmap.c
@@ -33,20 +33,17 @@ static void signal_handler(int sig)
siglongjmp(sigjmp_buf_env, -EFAULT);
}

-static int test_read_access(char *addr, size_t size, size_t pagesize)
+static int test_read_access(char *addr, size_t size)
{
- size_t offs;
int ret;

if (signal(SIGSEGV, signal_handler) == SIG_ERR)
return -EINVAL;

ret = sigsetjmp(sigjmp_buf_env, 1);
- if (!ret) {
- for (offs = 0; offs < size; offs += pagesize)
- /* Force a read that the compiler cannot optimize out. */
- *((volatile char *)(addr + offs));
- }
+ if (!ret)
+ force_read_pages_in_range(addr, size);
+
if (signal(SIGSEGV, SIG_DFL) == SIG_ERR)
return -EINVAL;

@@ -138,7 +135,7 @@ FIXTURE_SETUP(pfnmap)
SKIP(return, "Invalid file: '%s'. Not pfnmap'ed\n", file);

/* ... and want to be able to read from them. */
- if (test_read_access(self->addr1, self->size1, self->pagesize))
+ if (test_read_access(self->addr1, self->size1))
SKIP(return, "Cannot read-access mmap'ed '%s'\n", file);

self->size2 = 0;
@@ -243,8 +240,7 @@ TEST_F(pfnmap, fork)
ASSERT_GE(pid, 0);

if (!pid) {
- EXPECT_EQ(test_read_access(self->addr1, self->size1,
- self->pagesize), 0);
+ EXPECT_EQ(test_read_access(self->addr1, self->size1), 0);
exit(0);
}

diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 40799f3f0213..65a89ceca4a5 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -652,11 +652,7 @@ static int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size,
}
madvise(*addr, fd_size, MADV_HUGEPAGE);

- for (size_t i = 0; i < fd_size; i++) {
- char *addr2 = *addr + i;
-
- FORCE_READ(*addr2);
- }
+ force_read_pages_in_range(*addr, fd_size);

if (!check_huge_file(*addr, fd_size / pmd_pagesize, pmd_pagesize)) {
ksft_print_msg("No large pagecache folio generated, please provide a filesystem supporting large folio\n");
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 6ad32b1830f1..74bdf96161d7 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -54,6 +54,12 @@ static inline unsigned int pshift(void)
return __page_shift;
}

+static inline void force_read_pages_in_range(char *addr, size_t len)
+{
+ for (size_t i = 0; i < len; i += psize())
+ FORCE_READ(addr[i]);
+}
+
bool detect_huge_zeropage(void);

/*
--
2.51.2