Docker postgres work_mem not using ram

I have set shared_buffers to 256MB. Using pg_buffercache extension I see that all of the buffers are in use: SELECT pg_size_pretty(COUNT(*)*8192) as used FROM pg_buffercache; used ---------------- 256 MB Now the problem is that when I use docker stats to view the database container memory it shows: NAME CPU % MEM USAGE / LIMIT MEM % db 0.00% 31.07MiB / 1GiB 3.03% Where is the shared_buffers memory stored? Shouldn't be in ram and displayed in docker stats?