Re: [PATCH] selftests: cachestat: add tests for mmap

On Mon, Jun 30, 2025 at 11:08 AM Suresh K C suresh.k.chandrappa@gmail.com wrote:

From: Suresh K C suresh.k.chandrappa@gmail.com

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@gmail.com

FWIW, the tests passed :)

---

.../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';
  

•   }
  

Joshua is right. We're already doing the write_exactly() for both cases? Let's write_exactly() (i.e using the file descriptor-based write syscall) only for FILE_SHMEM.

And why do we need the 'X' at the end?