Re: [PATCH v2] selftests/cgroup: test_zswap: skip test_no_kmem_bypass if debugfs is unavailable

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 11 Aug 2026 05:14:11 +0000 Wilson Felipe Pereira <wfelipe@google.com> wrote:

> test_no_kmem_bypass() needs to read
> /sys/kernel/debug/zswap/stored_pages via get_zswap_stored_pages() to
> verify that compressed pages are charged to the memcg.
> 
> When running in an environment where debugfs is not mounted or
> CONFIG_DEBUG_FS is disabled, get_zswap_stored_pages() fails, causing the
> loop to terminate early and report a false negative (KSFT_FAIL).
> 
> Selftests should not fail if debugfs is unavailable, and it should print
> a message when it is skipped.
> 
> While I'm here, also add a warning message if the test is being skipped
> due to totalram size and make the check for totalram more readable.
> 
> ...
>
> --- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> +++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
>
> ...
>
> @@ -570,8 +571,16 @@ static int test_no_kmem_bypass(const char *root)
>  	/* Read sys info and compute test values accordingly */
>  	if (sysinfo(&sys_info) != 0)
>  		return KSFT_FAIL;
> -	if (sys_info.totalram > 5000000000)
> +	if (sys_info.totalram > GB(4)) {
> +		ksft_print_msg(
> +			"requires less than 4GB total ram, sys_info.totalram: %.1fGB\n",
> +			(double)sys_info.totalram / GB(1));
>  		return KSFT_SKIP;
> +	}
> +	if (access(PATH_ZSWAP_STORED_PAGES, R_OK)) {
> +		ksft_print_msg("mount debugfs at /sys/kernel/debug\n");

Super nittynit: "mount debugfs at /sys/kernel/debug" sounds like a
progress message.  "I just mounted debugfs at ...".  I think the below is
more clear?

--- a/tools/testing/selftests/cgroup/test_zswap.c~selftests-cgroup-test_zswap-skip-test_no_kmem_bypass-if-debugfs-is-unavailable-fix
+++ a/tools/testing/selftests/cgroup/test_zswap.c
@@ -578,7 +578,7 @@ static int test_no_kmem_bypass(const cha
 		return KSFT_SKIP;
 	}
 	if (access(PATH_ZSWAP_STORED_PAGES, R_OK)) {
-		ksft_print_msg("mount debugfs at /sys/kernel/debug\n");
+		ksft_print_msg("debugfs not mounted at /sys/kernel/debug\n");
 		return KSFT_SKIP;
 	}
 	values = mmap(0, sizeof(struct no_kmem_bypass_child_args), PROT_READ |
_