selftests/cgroup: include slab in test_percpu_basic memory check

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.

Link: https://lore.kernel.org/20260501022058.18024-3-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Reviewed-by: 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>
Cc: Sayali Patil <sayalip@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions