selftests/bpf: Retry stat generation in cgroup_iter_memcg

Each cgroup_iter_memcg subtest touches 1024 pages and expects the matching
memcg counter to be non-zero. On a host with many CPUs it reads zero
instead:

  test_anon:FAIL:final anon mapped val: actual 0 <= expected 0

memcg stats are cached per-cpu and only become visible once the periodic
flusher runs (FLUSH_TIME, 2s), or once pending updates cross
MEMCG_CHARGE_BATCH * num_online_cpus(). That threshold is 512 pages at 8
CPUs but 8192 at 128, so a single pass no longer reaches it and
bpf_mem_cgroup_flush_stats() returns without flushing anything.

Retry the stat generation, sleeping in between, so that a flusher cycle is
always covered. Sleep before dropping the mapping, so that a flusher cycle
landing in the sleep observes the mapped state. nr_anon_mapped and
nr_file_mapped are rmap gauges, and unmapping first would post a matching
negative delta for the flusher to aggregate to a net zero.

test_file asserts on both nr_file_pages and nr_file_mapped, which have
different lifetimes, as page cache pages outlive the mapping. Retry
while either one is still zero.

Fixes: 6bce6ddbe634 ("bpf: selftests: selftests for memcg stat kfuncs")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20260814232017.2839959-1-andrii@kernel.org

0 files changed, 0 insertions, 0 deletions