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

[SJ Park <sj@kernel.org>]

On Tue, 11 Aug 2026 19:06:11 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:

> 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?

+1.  I was feeling similar.

> 
> --- 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");

This reads better for me.  I also find this is more consistent to similar skip
messages in main() and check_zswap_enabled().

>  		return KSFT_SKIP;
>  	}
>  	values = mmap(0, sizeof(struct no_kmem_bypass_child_args), PROT_READ |
> _


Thanks,
SJ