selftests/cgroup: fix hardcoded page size in test_percpu_basic

Patch series "selftests/cgroup: Fix false positive failures in
test_percpu_basic", v2.

This patch series addresses two separate issues that cause false
positive failures in the test_percpu_basic test within the cgroup
kmem selftests.

The first issue stems from a hardcoded assumption about the system
page size, which breaks the test on architectures with larger page
sizes.

The second issue is an overly strict memory check that fails to
account for the slab metadata allocated during cgroup creation.


This patch (of 2):

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.

Link: https://lore.kernel.org/20260501022058.18024-1-li.wang@linux.dev
Link: https://lore.kernel.org/20260501022058.18024-2-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Waiman Long <longman@redhat.com>
Reviewed-by: Sayali Patil <sayalip@linux.ibm.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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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