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

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

[Wilson Felipe Pereira]

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.

Signed-off-by: Wilson Felipe Pereira <wfelipe@google.com>
---
v1 -> v2:
  - Check for debugfs availability using access("/sys/kernel/debug/zswap/stored_pages", R_OK)
    instead of calling get_zswap_stored_pages() (Yosry Ahmed).
  - Update debugfs print message to exactly match gup_test.c (Anshuman Khandual).
  - Add GB(x) macro to cgroup_util.h (Yosry Ahmed). Cast to unsigned long long
    to prevent 32-bit truncation without altering existing MB(x) signedness.
  - Update RAM check to GB(4) to match comments and format totalram output
    with 1 decimal place (%.1fGB) (Yosry Ahmed).
  - Fix commit message typo (Yosry Ahmed).
  - Moved stored_pages back inside the for loop.

v1: https://lore.kernel.org/all/20260801041255.752039-1-wfelipe@google.com/

 .../selftests/cgroup/lib/include/cgroup_util.h      |  1 +
 tools/testing/selftests/cgroup/test_zswap.c         | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
index febc1723d0903..c0f07226b222f 100644
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -7,6 +7,7 @@
 #endif

 #define MB(x) (x << 20)
+#define GB(x) ((unsigned long long)(x) << 30)

 #define USEC_PER_SEC	1000000L
 #define NSEC_PER_SEC	1000000000L
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 49b36ee791606..a836337440040 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -20,6 +20,7 @@ static int page_size;

 #define PATH_ZSWAP "/sys/module/zswap"
 #define PATH_ZSWAP_ENABLED "/sys/module/zswap/parameters/enabled"
+#define PATH_ZSWAP_STORED_PAGES "/sys/kernel/debug/zswap/stored_pages"

 static int read_int(const char *path, size_t *value)
 {
@@ -55,7 +56,7 @@ static int read_min_free_kb(size_t *value)

 static int get_zswap_stored_pages(size_t *value)
 {
-	return read_int("/sys/kernel/debug/zswap/stored_pages", value);
+	return read_int(PATH_ZSWAP_STORED_PAGES, value);
 }

 static long get_cg_wb_count(const char *cg)
@@ -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");
+		return KSFT_SKIP;
+	}
 	values = mmap(0, sizeof(struct no_kmem_bypass_child_args), PROT_READ |
 			PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 	if (values == MAP_FAILED)
--
2.55.0.679.g6767b8d81c-goog

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

[Yosry Ahmed]

On Mon, Aug 10, 2026 at 10:14 PM 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.
>
> Signed-off-by: Wilson Felipe Pereira <wfelipe@google.com>

Acked-by: Yosry Ahmed <yosry@kernel.org>

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

[Nhat Pham]

On Mon, Aug 10, 2026 at 10:14 PM 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.
>
> Signed-off-by: Wilson Felipe Pereira <wfelipe@google.com>

Acked-by: Nhat Pham <nphamcs@gmail.com>

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

[Andrew Morton]

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 |
_

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

[Anshuman Khandual]

On Tue, Aug 11, 2026 at 07:06:11PM -0700, Andrew Morton 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?
> 
> --- 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 is definitely more accurate.

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

I assume you would change this while applying the patch.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

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

[SJ Park]

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