[PATCH v2 1/2] selftests: cachestat: add tests for mmap

From: Suresh K C
Date: Tue Jul 01 2025 - 14:49:31 EST


From: Suresh K C <suresh.k.chandrappa@xxxxxxxxx>

Add a test case to verify cachestat behavior with memory-mapped files
using mmap(). This ensures that pages accessed via mmap are correctly
accounted for in the page cache.

Tested on x86_64 with default kernel config

Signed-off-by: Suresh K C <suresh.k.chandrappa@xxxxxxxxx>
---
.../selftests/cachestat/test_cachestat.c | 39 ++++++++++++++++---
1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
index 632ab44737ec..b6452978dae0 100644
--- a/tools/testing/selftests/cachestat/test_cachestat.c
+++ b/tools/testing/selftests/cachestat/test_cachestat.c
@@ -33,6 +33,11 @@ void print_cachestat(struct cachestat *cs)
cs->nr_evicted, cs->nr_recently_evicted);
}

+enum file_type {
+ FILE_MMAP,
+ FILE_SHMEM
+};
+
bool write_exactly(int fd, size_t filesize)
{
int random_fd = open("/dev/urandom", O_RDONLY);
@@ -202,7 +207,7 @@ static int test_cachestat(const char *filename, bool write_random, bool create,
return ret;
}

-bool test_cachestat_shmem(void)
+bool run_cachestat_test(enum file_type type)
{
size_t PS = sysconf(_SC_PAGESIZE);
size_t filesize = PS * 512 * 2; /* 2 2MB huge pages */
@@ -212,27 +217,43 @@ bool test_cachestat_shmem(void)
char *filename = "tmpshmcstat";
struct cachestat cs;
bool ret = true;
+ int fd;
unsigned long num_pages = compute_len / PS;
- int fd = shm_open(filename, O_CREAT | O_RDWR, 0600);
+ if (type == FILE_SHMEM)
+ fd = shm_open(filename, O_CREAT | O_RDWR, 0600);
+ else
+ fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);

if (fd < 0) {
- ksft_print_msg("Unable to create shmem file.\n");
+ ksft_print_msg("Unable to create file.\n");
ret = false;
goto out;
}

if (ftruncate(fd, filesize)) {
- ksft_print_msg("Unable to truncate shmem file.\n");
+ ksft_print_msg("Unable to truncate file.\n");
ret = false;
goto close_fd;
}

if (!write_exactly(fd, filesize)) {
- ksft_print_msg("Unable to write to shmem file.\n");
+ ksft_print_msg("Unable to write to file.\n");
ret = false;
goto close_fd;
}

+ if (type == FILE_MMAP){
+ char *map = mmap(NULL, filesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+ if (map == MAP_FAILED) {
+ ksft_print_msg("mmap failed.\n");
+ ret = false;
+ goto close_fd;
+ }
+ for (int i = 0; i < filesize; i++) {
+ map[i] = 'A';
+ }
+ map[filesize - 1] = 'X';
+ }
syscall_ret = syscall(__NR_cachestat, fd, &cs_range, &cs, 0);

if (syscall_ret) {
@@ -308,12 +329,18 @@ int main(void)
break;
}

- if (test_cachestat_shmem())
+ if (run_cachestat_test(FILE_SHMEM))
ksft_test_result_pass("cachestat works with a shmem file\n");
else {
ksft_test_result_fail("cachestat fails with a shmem file\n");
ret = 1;
}

+ if (run_cachestat_test(FILE_MMAP))
+ ksft_test_result_pass("cachestat works with a mmap file\n");
+ else {
+ ksft_test_result_fail("cachestat fails with a mmap file\n");
+ ret = 1;
+ }
return ret;
}
--
2.43.0