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selftests/cgroup: include slab in test_percpu_basic memory check

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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>
This commit is contained in:
Li Wang 2026-05-01 10:20:58 +08:00 committed by Andrew Morton
parent ca9caa098f
commit 5de852b6e7
1 changed files with 6 additions and 5 deletions
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11
tools/testing/selftests/cgroup/test_kmem.c
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@ -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");
@ -383,13 +383,14 @@ 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++) {