[PATCH bpf-next v4 0/3] Fix test_cgroup_iter_memcg issues found during back-porting

[PATCH bpf-next v4 0/3] Fix test_cgroup_iter_memcg issues found during back-porting

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

While back-porting "mm: bpf kfuncs to access memcg data", I
encountered issues with test_cgroup_iter_memcg, specifically
in test_kmem.

These patches are my fixes for the problems I encountered.

Changelog:
v4:
Fixed wrong git commit log in "bpf: Use bpf_core_enum_value for stats in
cgroup_iter_memcg".
v3:
According to the comments of JP Kobryn, remove kmem subtest from
cgroup_iter_memcg and fix assertion string in test_pgfault.
v2:
According to the comments of JP Kobryn, added bpf_core_enum_value()
usage in the BPF program to handle cross-kernel enum value differences
at load-time instead of compile-time.
Dropped the mm/memcontrol.c patch.
Modified test_kmem handling: instead of skipping when nokmem is set,
verify that kmem value is zero as expected.
According to the comments of bot, fixed assertion message: changed
"bpf_mem_cgroup_page_state" to "bpf_mem_cgroup_vm_events" for PGFAULT
check.

Hui Zhu (3):
  selftests/bpf: Remove kmem subtest from cgroup_iter_memcg
  bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg
  selftests/bpf: Check bpf_mem_cgroup_page_state return value

 .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 -
 .../bpf/prog_tests/cgroup_iter_memcg.c        | 38 +++++--------------
 .../selftests/bpf/progs/cgroup_iter_memcg.c   | 18 ++++++---
 3 files changed, 22 insertions(+), 36 deletions(-)

-- 
2.43.0

[PATCH bpf-next v4 1/3] selftests/bpf: Remove kmem subtest from cgroup_iter_memcg

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

When cgroup.memory=nokmem is set in the kernel command line, kmem
accounting is disabled. This causes the test_kmem subtest in
cgroup_iter_memcg to fail because it expects non-zero kmem values.

Remove the kmem subtest altogether since the remaining subtests
(shmem, file, pgfault) already provide sufficient coverage for
the cgroup iter memcg functionality.

Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 --
 .../bpf/prog_tests/cgroup_iter_memcg.c        | 28 -------------------
 .../selftests/bpf/progs/cgroup_iter_memcg.c   |  1 -
 3 files changed, 31 deletions(-)

diff --git a/tools/testing/selftests/bpf/cgroup_iter_memcg.h b/tools/testing/selftests/bpf/cgroup_iter_memcg.h
index 3f59b127943b..ff20ec537164 100644
--- a/tools/testing/selftests/bpf/cgroup_iter_memcg.h
+++ b/tools/testing/selftests/bpf/cgroup_iter_memcg.h
@@ -9,8 +9,6 @@ struct memcg_query {
 	unsigned long nr_shmem;
 	unsigned long nr_file_pages;
 	unsigned long nr_file_mapped;
-	/* some memcg_stat_item */
-	unsigned long memcg_kmem;
 	/* some vm_event_item */
 	unsigned long pgfault;
 };
diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
index a5afd16705f0..88fc3e83d2b7 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
@@ -126,32 +126,6 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
 	shm_unlink("/tmp_shmem");
 }
 
-#define NR_PIPES 64
-static void test_kmem(struct bpf_link *link, struct memcg_query *memcg_query)
-{
-	int fds[NR_PIPES][2], i;
-
-	/*
-	 * Increase kmem value by creating pipes which will allocate some
-	 * kernel buffers.
-	 */
-	for (i = 0; i < NR_PIPES; i++) {
-		if (!ASSERT_OK(pipe(fds[i]), "pipe"))
-			goto cleanup;
-	}
-
-	if (!ASSERT_OK(read_stats(link), "read stats"))
-		goto cleanup;
-
-	ASSERT_GT(memcg_query->memcg_kmem, 0, "kmem value");
-
-cleanup:
-	for (i = i - 1; i >= 0; i--) {
-		close(fds[i][0]);
-		close(fds[i][1]);
-	}
-}
-
 static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
 {
 	void *map;
@@ -209,8 +183,6 @@ void test_cgroup_iter_memcg(void)
 		test_shmem(link, &skel->data_query->memcg_query);
 	if (test__start_subtest("cgroup_iter_memcg__file"))
 		test_file(link, &skel->data_query->memcg_query);
-	if (test__start_subtest("cgroup_iter_memcg__kmem"))
-		test_kmem(link, &skel->data_query->memcg_query);
 	if (test__start_subtest("cgroup_iter_memcg__pgfault"))
 		test_pgfault(link, &skel->data_query->memcg_query);
 
diff --git a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
index 59fb70a3cc50..12f79a44133e 100644
--- a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
+++ b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
@@ -30,7 +30,6 @@ int cgroup_memcg_query(struct bpf_iter__cgroup *ctx)
 	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(memcg, NR_SHMEM);
 	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(memcg, NR_FILE_PAGES);
 	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(memcg, NR_FILE_MAPPED);
-	memcg_query.memcg_kmem = bpf_mem_cgroup_page_state(memcg, MEMCG_KMEM);
 	memcg_query.pgfault = bpf_mem_cgroup_vm_events(memcg, PGFAULT);
 
 	bpf_put_mem_cgroup(memcg);
-- 
2.43.0

[PATCH bpf-next v4 2/3] bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

Replace hardcoded enum values with bpf_core_enum_value() calls in
cgroup_iter_memcg test to improve portability across different
kernel versions.

The change adds runtime enum value resolution for:
- node_stat_item: NR_ANON_MAPPED, NR_SHMEM, NR_FILE_PAGES,
  NR_FILE_MAPPED
- vm_event_item: PGFAULT

This ensures the BPF program can adapt to enum value changes
between kernel versions.

Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 .../selftests/bpf/progs/cgroup_iter_memcg.c     | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
index 12f79a44133e..06a385c9d85b 100644
--- a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
+++ b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
@@ -26,11 +26,18 @@ int cgroup_memcg_query(struct bpf_iter__cgroup *ctx)
 
 	bpf_mem_cgroup_flush_stats(memcg);
 
-	memcg_query.nr_anon_mapped = bpf_mem_cgroup_page_state(memcg, NR_ANON_MAPPED);
-	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(memcg, NR_SHMEM);
-	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(memcg, NR_FILE_PAGES);
-	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(memcg, NR_FILE_MAPPED);
-	memcg_query.pgfault = bpf_mem_cgroup_vm_events(memcg, PGFAULT);
+	memcg_query.nr_anon_mapped = bpf_mem_cgroup_page_state(
+		memcg,
+		bpf_core_enum_value(enum node_stat_item, NR_ANON_MAPPED));
+	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(
+		memcg, bpf_core_enum_value(enum node_stat_item, NR_SHMEM));
+	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(
+		memcg, bpf_core_enum_value(enum node_stat_item, NR_FILE_PAGES));
+	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(
+		memcg,
+		bpf_core_enum_value(enum node_stat_item, NR_FILE_MAPPED));
+	memcg_query.pgfault = bpf_mem_cgroup_vm_events(
+		memcg, bpf_core_enum_value(enum vm_event_item, PGFAULT));
 
 	bpf_put_mem_cgroup(memcg);
 
-- 
2.43.0

[PATCH bpf-next v4 3/3] selftests/bpf: Check bpf_mem_cgroup_page_state return value

[Hui Zhu]

From: Hui Zhu <zhuhui@kylinos.cn>

When back-porting test_progs to different kernel versions, I encountered
an issue where the test_cgroup_iter_memcg test would falsely pass even
when bpf_mem_cgroup_page_state() failed.

This patch adds explicit checks to ensure bpf_mem_cgroup_page_state()
doesn't return -1 before validating the actual statistics values.

Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 .../selftests/bpf/prog_tests/cgroup_iter_memcg.c       | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
index 88fc3e83d2b7..9eadfbd3fdb9 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
@@ -53,6 +53,8 @@ static void test_anon(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->nr_anon_mapped, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_ANON_MAPPED");
 	ASSERT_GT(memcg_query->nr_anon_mapped, 0, "final anon mapped val");
 
 cleanup:
@@ -88,6 +90,10 @@ static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup_map;
 
+	ASSERT_NEQ(memcg_query->nr_file_pages, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_FILE_PAGES");
+	ASSERT_NEQ(memcg_query->nr_file_mapped, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_FILE_MAPPED");
 	ASSERT_GT(memcg_query->nr_file_pages, 0, "final file value");
 	ASSERT_GT(memcg_query->nr_file_mapped, 0, "final file mapped value");
 
@@ -119,6 +125,8 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->nr_shmem, (unsigned long)-1,
+		  "bpf_mem_cgroup_page_state NR_SHMEM");
 	ASSERT_GT(memcg_query->nr_shmem, 0, "final shmem value");
 
 cleanup:
@@ -144,6 +152,8 @@ static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
 	if (!ASSERT_OK(read_stats(link), "read stats"))
 		goto cleanup;
 
+	ASSERT_NEQ(memcg_query->pgfault, (unsigned long)-1,
+		  "bpf_mem_cgroup_vm_events PGFAULT");
 	ASSERT_GT(memcg_query->pgfault, 0, "final pgfault val");
 
 cleanup:
-- 
2.43.0

Re: [PATCH bpf-next v4 1/3] selftests/bpf: Remove kmem subtest from cgroup_iter_memcg

[JP Kobryn (Meta)]

On 2/28/26 1:25 AM, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
> 
> When cgroup.memory=nokmem is set in the kernel command line, kmem
> accounting is disabled. This causes the test_kmem subtest in
> cgroup_iter_memcg to fail because it expects non-zero kmem values.
> 
> Remove the kmem subtest altogether since the remaining subtests
> (shmem, file, pgfault) already provide sufficient coverage for
> the cgroup iter memcg functionality.
> 
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
> ---
>   .../testing/selftests/bpf/cgroup_iter_memcg.h |  2 --
>   .../bpf/prog_tests/cgroup_iter_memcg.c        | 28 -------------------
>   .../selftests/bpf/progs/cgroup_iter_memcg.c   |  1 -
>   3 files changed, 31 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/cgroup_iter_memcg.h b/tools/testing/selftests/bpf/cgroup_iter_memcg.h
> index 3f59b127943b..ff20ec537164 100644
> --- a/tools/testing/selftests/bpf/cgroup_iter_memcg.h
> +++ b/tools/testing/selftests/bpf/cgroup_iter_memcg.h
> @@ -9,8 +9,6 @@ struct memcg_query {
>   	unsigned long nr_shmem;
>   	unsigned long nr_file_pages;
>   	unsigned long nr_file_mapped;
> -	/* some memcg_stat_item */
> -	unsigned long memcg_kmem;
>   	/* some vm_event_item */
>   	unsigned long pgfault;
>   };
> diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
> index a5afd16705f0..88fc3e83d2b7 100644
> --- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
> +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
> @@ -126,32 +126,6 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
>   	shm_unlink("/tmp_shmem");
>   }
>   
> -#define NR_PIPES 64
> -static void test_kmem(struct bpf_link *link, struct memcg_query *memcg_query)
> -{
> -	int fds[NR_PIPES][2], i;
> -
> -	/*
> -	 * Increase kmem value by creating pipes which will allocate some
> -	 * kernel buffers.
> -	 */
> -	for (i = 0; i < NR_PIPES; i++) {
> -		if (!ASSERT_OK(pipe(fds[i]), "pipe"))
> -			goto cleanup;
> -	}
> -
> -	if (!ASSERT_OK(read_stats(link), "read stats"))
> -		goto cleanup;
> -
> -	ASSERT_GT(memcg_query->memcg_kmem, 0, "kmem value");
> -
> -cleanup:
> -	for (i = i - 1; i >= 0; i--) {
> -		close(fds[i][0]);
> -		close(fds[i][1]);
> -	}
> -}
> -
>   static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
>   {
>   	void *map;
> @@ -209,8 +183,6 @@ void test_cgroup_iter_memcg(void)
>   		test_shmem(link, &skel->data_query->memcg_query);
>   	if (test__start_subtest("cgroup_iter_memcg__file"))
>   		test_file(link, &skel->data_query->memcg_query);
> -	if (test__start_subtest("cgroup_iter_memcg__kmem"))
> -		test_kmem(link, &skel->data_query->memcg_query);
>   	if (test__start_subtest("cgroup_iter_memcg__pgfault"))
>   		test_pgfault(link, &skel->data_query->memcg_query);
>   
> diff --git a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
> index 59fb70a3cc50..12f79a44133e 100644
> --- a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
> +++ b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
> @@ -30,7 +30,6 @@ int cgroup_memcg_query(struct bpf_iter__cgroup *ctx)
>   	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(memcg, NR_SHMEM);
>   	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(memcg, NR_FILE_PAGES);
>   	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(memcg, NR_FILE_MAPPED);
> -	memcg_query.memcg_kmem = bpf_mem_cgroup_page_state(memcg, MEMCG_KMEM);
>   	memcg_query.pgfault = bpf_mem_cgroup_vm_events(memcg, PGFAULT);
>   
>   	bpf_put_mem_cgroup(memcg);

Reviewed-by: JP Kobryn <jp.kobryn@linux.dev>

Re: [PATCH bpf-next v4 2/3] bpf: Use bpf_core_enum_value for stats in cgroup_iter_memcg

[JP Kobryn (Meta)]

On 2/28/26 1:25 AM, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
> 
> Replace hardcoded enum values with bpf_core_enum_value() calls in
> cgroup_iter_memcg test to improve portability across different
> kernel versions.
> 
> The change adds runtime enum value resolution for:
> - node_stat_item: NR_ANON_MAPPED, NR_SHMEM, NR_FILE_PAGES,
>    NR_FILE_MAPPED
> - vm_event_item: PGFAULT
> 
> This ensures the BPF program can adapt to enum value changes
> between kernel versions.
> 
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
> ---
>   .../selftests/bpf/progs/cgroup_iter_memcg.c     | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
> index 12f79a44133e..06a385c9d85b 100644
> --- a/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
> +++ b/tools/testing/selftests/bpf/progs/cgroup_iter_memcg.c
> @@ -26,11 +26,18 @@ int cgroup_memcg_query(struct bpf_iter__cgroup *ctx)
>   
>   	bpf_mem_cgroup_flush_stats(memcg);
>   
> -	memcg_query.nr_anon_mapped = bpf_mem_cgroup_page_state(memcg, NR_ANON_MAPPED);
> -	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(memcg, NR_SHMEM);
> -	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(memcg, NR_FILE_PAGES);
> -	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(memcg, NR_FILE_MAPPED);
> -	memcg_query.pgfault = bpf_mem_cgroup_vm_events(memcg, PGFAULT);
> +	memcg_query.nr_anon_mapped = bpf_mem_cgroup_page_state(
> +		memcg,
> +		bpf_core_enum_value(enum node_stat_item, NR_ANON_MAPPED));
> +	memcg_query.nr_shmem = bpf_mem_cgroup_page_state(
> +		memcg, bpf_core_enum_value(enum node_stat_item, NR_SHMEM));
> +	memcg_query.nr_file_pages = bpf_mem_cgroup_page_state(
> +		memcg, bpf_core_enum_value(enum node_stat_item, NR_FILE_PAGES));
> +	memcg_query.nr_file_mapped = bpf_mem_cgroup_page_state(
> +		memcg,
> +		bpf_core_enum_value(enum node_stat_item, NR_FILE_MAPPED));
> +	memcg_query.pgfault = bpf_mem_cgroup_vm_events(
> +		memcg, bpf_core_enum_value(enum vm_event_item, PGFAULT));
>   
>   	bpf_put_mem_cgroup(memcg);
>   

Reviewed-by: JP Kobryn <jp.kobryn@linux.dev>

Re: [PATCH bpf-next v4 3/3] selftests/bpf: Check bpf_mem_cgroup_page_state return value

[JP Kobryn (Meta)]

On 2/28/26 1:25 AM, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
> 
> When back-porting test_progs to different kernel versions, I encountered
> an issue where the test_cgroup_iter_memcg test would falsely pass even
> when bpf_mem_cgroup_page_state() failed.
> 
> This patch adds explicit checks to ensure bpf_mem_cgroup_page_state()
> doesn't return -1 before validating the actual statistics values.
> 
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
> ---
>   .../selftests/bpf/prog_tests/cgroup_iter_memcg.c       | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
> index 88fc3e83d2b7..9eadfbd3fdb9 100644
> --- a/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
> +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
> @@ -53,6 +53,8 @@ static void test_anon(struct bpf_link *link, struct memcg_query *memcg_query)
>   	if (!ASSERT_OK(read_stats(link), "read stats"))
>   		goto cleanup;
>   
> +	ASSERT_NEQ(memcg_query->nr_anon_mapped, (unsigned long)-1,
> +		  "bpf_mem_cgroup_page_state NR_ANON_MAPPED");
>   	ASSERT_GT(memcg_query->nr_anon_mapped, 0, "final anon mapped val");
>   
>   cleanup:
> @@ -88,6 +90,10 @@ static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
>   	if (!ASSERT_OK(read_stats(link), "read stats"))
>   		goto cleanup_map;
>   
> +	ASSERT_NEQ(memcg_query->nr_file_pages, (unsigned long)-1,
> +		  "bpf_mem_cgroup_page_state NR_FILE_PAGES");
> +	ASSERT_NEQ(memcg_query->nr_file_mapped, (unsigned long)-1,
> +		  "bpf_mem_cgroup_page_state NR_FILE_MAPPED");
>   	ASSERT_GT(memcg_query->nr_file_pages, 0, "final file value");
>   	ASSERT_GT(memcg_query->nr_file_mapped, 0, "final file mapped value");
>   
> @@ -119,6 +125,8 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
>   	if (!ASSERT_OK(read_stats(link), "read stats"))
>   		goto cleanup;
>   
> +	ASSERT_NEQ(memcg_query->nr_shmem, (unsigned long)-1,
> +		  "bpf_mem_cgroup_page_state NR_SHMEM");
>   	ASSERT_GT(memcg_query->nr_shmem, 0, "final shmem value");
>   
>   cleanup:
> @@ -144,6 +152,8 @@ static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
>   	if (!ASSERT_OK(read_stats(link), "read stats"))
>   		goto cleanup;
>   
> +	ASSERT_NEQ(memcg_query->pgfault, (unsigned long)-1,
> +		  "bpf_mem_cgroup_vm_events PGFAULT");
>   	ASSERT_GT(memcg_query->pgfault, 0, "final pgfault val");
>   
>   cleanup:

Emil mentioned in the v3 thread that we don't need these checks [0]. I
agree. Now that you're using the bpf co-re enum helpers, the stat
indexes won't become an issue in a cross-kernel secenario. This patch
can be dropped.

[0] 
https://lore.kernel.org/bpf/DGQXZVBSVEUP.35P5G9QOL9EAT@etsalapatis.com/T/#m7cb6edf90ed4daaeda38b746363317405f198f20