[PATCH 1/2] selftests/cgroup: Fix hardcoded page size in test_percpu_basic

[PATCH 1/2] selftests/cgroup: Fix hardcoded page size in test_percpu_basic

[Li Wang]

MAX_VMSTAT_ERROR uses a hardcoded page size of 4096, which assumes
4K pages. This causes test_percpu_basic to fail on systems where
the kernel is configured with a larger page size, such as aarch64
systems using 16K or 64K pages, where the maximum permissible
discrepancy between memory.current and percpu charges is
proportionally larger.

Replace the hardcoded 4096 with sysconf(_SC_PAGESIZE) to correctly
derive the page size at runtime regardless of the underlying
architecture or kernel configuration.

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
---
 tools/testing/selftests/cgroup/test_kmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index eeabd34bf083..249d79113067 100644
--- a/tools/testing/selftests/cgroup/test_kmem.c
+++ b/tools/testing/selftests/cgroup/test_kmem.c
@@ -24,7 +24,7 @@
  * the maximum discrepancy between charge and vmstat entries is number
  * of cpus multiplied by 64 pages.
  */
-#define MAX_VMSTAT_ERROR (4096 * 64 * get_nprocs())
+#define MAX_VMSTAT_ERROR (sysconf(_SC_PAGESIZE) * 64 * get_nprocs())
 
 #define KMEM_DEAD_WAIT_RETRIES        80
 
-- 
2.53.0

[PATCH 2/2] selftests/cgroup: include slab in test_percpu_basic memory check

[Li Wang]

test_percpu_basic() currently compares memory.current against only
memory.stat:percpu after creating 1000 child cgroups.

Observed failure:
  #./test_kmem
  ok 1 test_kmem_basic
  ok 2 test_kmem_memcg_deletion
  ok 3 test_kmem_proc_kpagecgroup
  ok 4 test_kmem_kernel_stacks
  ok 5 test_kmem_dead_cgroups
  memory.current 11530240
  percpu 8440000
  not ok 6 test_percpu_basic

That assumption is too strict: child cgroup creation also allocates
slab-backed metadata, so memory.current is expected to be larger than
percpu alone. One visible path is:

  cgroup_mkdir()
    cgroup_create()
      cgroup_addrm_file()
        cgroup_add_file()
          __kernfs_create_file()
            __kernfs_new_node()
              kmem_cache_zalloc()

These kernfs allocations are charged as slab and show up in
memory.stat:slab.

Update the check to compare memory.current against (percpu + slab)
within MAX_VMSTAT_ERROR, and print slab/delta in the failure message to
improve diagnostics.

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
---
 tools/testing/selftests/cgroup/test_kmem.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index 249d79113067..4b5799698893 100644
--- a/tools/testing/selftests/cgroup/test_kmem.c
+++ b/tools/testing/selftests/cgroup/test_kmem.c
@@ -353,7 +353,7 @@ static int test_percpu_basic(const char *root)
 {
 	int ret = KSFT_FAIL;
 	char *parent, *child;
-	long current, percpu;
+	long current, percpu, slab;
 	int i;
 
 	parent = cg_name(root, "percpu_basic_test");
@@ -379,13 +379,14 @@ static int test_percpu_basic(const char *root)
 
 	current = cg_read_long(parent, "memory.current");
 	percpu = cg_read_key_long(parent, "memory.stat", "percpu ");
+	slab = cg_read_key_long(parent, "memory.stat", "slab ");
 
-	if (current > 0 && percpu > 0 && labs(current - percpu) <
-	    MAX_VMSTAT_ERROR)
+	if (current > 0 && percpu > 0 && slab >= 0 &&
+			labs(current - (percpu + slab)) < MAX_VMSTAT_ERROR)
 		ret = KSFT_PASS;
 	else
-		printf("memory.current %ld\npercpu %ld\n",
-		       current, percpu);
+		printf("memory.current %ld\npercpu %ld\nslab %ld\ndelta %ld\n",
+			current, percpu, slab, current - (percpu + slab));
 
 cleanup_children:
 	for (i = 0; i < 1000; i++) {
-- 
2.53.0

Re: [PATCH 2/2] selftests/cgroup: include slab in test_percpu_basic memory check

[Waiman Long]

On 3/6/26 2:18 AM, Li Wang wrote:
> test_percpu_basic() currently compares memory.current against only
> memory.stat:percpu after creating 1000 child cgroups.
>
> Observed failure:
>    #./test_kmem
>    ok 1 test_kmem_basic
>    ok 2 test_kmem_memcg_deletion
>    ok 3 test_kmem_proc_kpagecgroup
>    ok 4 test_kmem_kernel_stacks
>    ok 5 test_kmem_dead_cgroups
>    memory.current 11530240
>    percpu 8440000
>    not ok 6 test_percpu_basic
>
> That assumption is too strict: child cgroup creation also allocates
> slab-backed metadata, so memory.current is expected to be larger than
> percpu alone. One visible path is:
>
>    cgroup_mkdir()
>      cgroup_create()
>        cgroup_addrm_file()
>          cgroup_add_file()
>            __kernfs_create_file()
>              __kernfs_new_node()
>                kmem_cache_zalloc()
>
> These kernfs allocations are charged as slab and show up in
> memory.stat:slab.
>
> Update the check to compare memory.current against (percpu + slab)
> within MAX_VMSTAT_ERROR, and print slab/delta in the failure message to
> improve diagnostics.
>
> Signed-off-by: Li Wang <liwang@redhat.com>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> ---
>   tools/testing/selftests/cgroup/test_kmem.c | 11 ++++++-----
>   1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
> index 249d79113067..4b5799698893 100644
> --- a/tools/testing/selftests/cgroup/test_kmem.c
> +++ b/tools/testing/selftests/cgroup/test_kmem.c
> @@ -353,7 +353,7 @@ static int test_percpu_basic(const char *root)
>   {
>   	int ret = KSFT_FAIL;
>   	char *parent, *child;
> -	long current, percpu;
> +	long current, percpu, slab;
>   	int i;
>   
>   	parent = cg_name(root, "percpu_basic_test");
> @@ -379,13 +379,14 @@ static int test_percpu_basic(const char *root)
>   
>   	current = cg_read_long(parent, "memory.current");
>   	percpu = cg_read_key_long(parent, "memory.stat", "percpu ");
> +	slab = cg_read_key_long(parent, "memory.stat", "slab ");
>   
> -	if (current > 0 && percpu > 0 && labs(current - percpu) <
> -	    MAX_VMSTAT_ERROR)
> +	if (current > 0 && percpu > 0 && slab >= 0 &&
> +			labs(current - (percpu + slab)) < MAX_VMSTAT_ERROR)
>   		ret = KSFT_PASS;
>   	else
> -		printf("memory.current %ld\npercpu %ld\n",
> -		       current, percpu);
> +		printf("memory.current %ld\npercpu %ld\nslab %ld\ndelta %ld\n",
> +			current, percpu, slab, current - (percpu + slab));
>   
>   cleanup_children:
>   	for (i = 0; i < 1000; i++) {
Reviewed-by: Waiman Long <longman@redhat.com>

Re: [PATCH 1/2] selftests/cgroup: Fix hardcoded page size in test_percpu_basic

[Waiman Long]

On 3/6/26 2:18 AM, Li Wang wrote:
> MAX_VMSTAT_ERROR uses a hardcoded page size of 4096, which assumes
> 4K pages. This causes test_percpu_basic to fail on systems where
> the kernel is configured with a larger page size, such as aarch64
> systems using 16K or 64K pages, where the maximum permissible
> discrepancy between memory.current and percpu charges is
> proportionally larger.
>
> Replace the hardcoded 4096 with sysconf(_SC_PAGESIZE) to correctly
> derive the page size at runtime regardless of the underlying
> architecture or kernel configuration.
>
> Signed-off-by: Li Wang <liwang@redhat.com>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> ---
>   tools/testing/selftests/cgroup/test_kmem.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
> index eeabd34bf083..249d79113067 100644
> --- a/tools/testing/selftests/cgroup/test_kmem.c
> +++ b/tools/testing/selftests/cgroup/test_kmem.c
> @@ -24,7 +24,7 @@
>    * the maximum discrepancy between charge and vmstat entries is number
>    * of cpus multiplied by 64 pages.
>    */
> -#define MAX_VMSTAT_ERROR (4096 * 64 * get_nprocs())
> +#define MAX_VMSTAT_ERROR (sysconf(_SC_PAGESIZE) * 64 * get_nprocs())
>   
>   #define KMEM_DEAD_WAIT_RETRIES        80
>   

That is the right change for now. However, I have sent out patches that 
change the way vmstats flush threshold is being computed, so it may need 
to be changed again in the future if the threshold is indeed updated. 
Anyway,

Acked-by: Waiman Long <longman@redhat.com>

Re: [PATCH 1/2] selftests/cgroup: Fix hardcoded page size in test_percpu_basic

[Li Wang]

Hello All,

Gental ping~
Any more review comments will be appreciated!

-- 
Regards,
Li Wang