linux-kernel - Re: [PATCH] selftests: cachestat: add tests for mmap and /proc/cpuinfo

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Message-ID: <CAKEwX=MGgNw6rq1Y+gao=_AKP+hjuck-dafeaEs18YB21gGQKA@mail.gmail.com>
Date: Wed, 4 Jun 2025 10:55:58 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Suresh K C <suresh.k.chandrappa@...il.com>
Cc: hannes@...xchg.org, shuah@...nel.org, linux-mm@...ck.org, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: cachestat: add tests for mmap and /proc/cpuinfo

On Sat, May 24, 2025 at 1:36 AM Suresh K C
<suresh.k.chandrappa@...il.com> wrote:
>
> From: Suresh K C <suresh.k.chandrappa@...il.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.
>
> Also add a test for /proc/cpuinfo to validate cachestat's handling of
> virtual files in pseudo-filesystems. This improves test coverage for

Hmm, it's been awhile since I wrote these tests, but isn't there
already a test for /proc/* files?

> edge cases involving non-regular files.
>
> Tested on x86_64 with default kernel config.
>
> Signed-off-by: Suresh K C <suresh.k.chandrappa@...il.com>
> ---
>  .../selftests/cachestat/test_cachestat.c      | 69 ++++++++++++++++++-
>  1 file changed, 67 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
> index 632ab44737ec..81e7f6dd2279 100644
> --- a/tools/testing/selftests/cachestat/test_cachestat.c
> +++ b/tools/testing/selftests/cachestat/test_cachestat.c
> @@ -22,7 +22,7 @@
>
>  static const char * const dev_files[] = {
>         "/dev/zero", "/dev/null", "/dev/urandom",
> -       "/proc/version", "/proc"
> +       "/proc/version","/proc/cpuinfo","/proc"
>  };
>
>  void print_cachestat(struct cachestat *cs)
> @@ -202,6 +202,65 @@ static int test_cachestat(const char *filename, bool write_random, bool create,
>         return ret;
>  }
>
> +bool test_cachestat_mmap(void){
> +
> +       size_t PS = sysconf(_SC_PAGESIZE);
> +       size_t filesize = PS * 512 * 2;;
> +       int syscall_ret;
> +       size_t compute_len = PS * 512;
> +       struct cachestat_range cs_range = { PS, compute_len };
> +       char *filename = "tmpshmcstat";
> +       unsigned long num_pages = compute_len / PS;
> +       struct cachestat cs;
> +       bool ret = true;
> +       int fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);
> +       if (fd < 0) {
> +               ksft_print_msg("Unable to create mmap file.\n");
> +               ret = false;
> +               goto out;
> +       }
> +       if (ftruncate(fd, filesize)) {
> +               ksft_print_msg("Unable to truncate mmap file.\n");
> +               ret = false;
> +               goto close_fd;
> +       }
> +       if (!write_exactly(fd, filesize)) {
> +               ksft_print_msg("Unable to write to mmap file.\n");
> +               ret = false;
> +               goto close_fd;
> +       }
> +       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) {
> +               ksft_print_msg("Cachestat returned non-zero.\n");
> +               ret = false;
> +       } else {
> +               print_cachestat(&cs);
> +               if (cs.nr_cache + cs.nr_evicted != num_pages) {
> +                       ksft_print_msg("Total number of cached and evicted pages is off.\n");
> +                       ret = false;
> +               }
> +       }
> +
> +close_fd:
> +       close(fd);
> +       unlink(filename);
> +out:
> +       return ret;
> +}
> +

This looks 90% the same as another test. Are we literally just adding
the mmap step to test_cachestat and call it a new test?

Can we at least refactor things?