Okay, setting CONFIG_MEMCG fixed it:
gentooC01 ~ # mount | grep cgroup
cgroup_root on /sys/fs/cgroup type tmpfs (rw,nosuid,nodev,noexec,relatime,size=10240k,mode=755,uid=1000000,gid=1000000)
openrc on /sys/fs/cgroup/openrc type cgroup (rw,nosuid,nodev,noexec,relatime,release_agent=/lib/rc/sh/cgroup-release-agent.sh,name=openrc)
none on /sys/fs/cgroup/unified type cgroup2 (rw,nosuid,nodev,noexec,relatime)
cpuset on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
cpu on /sys/fs/cgroup/cpu type cgroup (rw,nosuid,nodev,noexec,relatime,cpu)
cpuacct on /sys/fs/cgroup/cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct)
memory on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
devices on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
freezer on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
net_cls on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
gentooC01 ~ # free
total used free shared buff/cache available
Mem: 1000000 4372 989292 0 6336 995628
Swap: 0 0 0