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@xxxxxxxxxx>
> Cc: Waiman Long <longman@xxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>   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@xxxxxxxxxx>