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

[Suresh K C]

From: Suresh K C <suresh.k.chandra...@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.chandra...@gmail.com>
---
 .../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