CODEWITHSUNDEEP
python-3.xdockerdocker-compose
Francesco Meli
Francesco Meli

Reputation: 2700

Docker container memory usage seems incorrect

I have a container mounted using docker-compose version 2 which has a memory limit on it of 32mb.

Whenever I run the container I can monitor the used resources like so:

docker stats 02bbab9ae853

It shows the following: 

CONTAINER ID        NAME                                            CPU %               MEM USAGE / LIMIT   MEM %               NET I/O             BLOCK I/O           PIDS
02bbab9ae853        client-web_postgres-client-web_1_e4513764c3e7   0.07%               8.078MiB / 32MiB    25.24%              5.59MB / 4.4MB      135GB / 23.7MB      0

What looks really weird to me is the memory part:

8.078MiB / 32MiB    25.24%

If outside the container I list of Postgres PIDs I get:

$ pgrep postgres
23051, 24744, 24745, 24746, 24747, 24748, 24749, 24753, 24761

If I stop the container and re-run the above command I get no PID. That is a clear proof that all PID where created by the stopped container.

Now, if I re-run the container and get every PID and I calculate its RSS memory usage and I sum it together with a python method, I don't get ~8Mb docker is telling me but a much higher value not even close to it (like ~100Mb or so).

This is the python method I'm using to calculate the RSS memory:

def get_process_memory(name):
    total = 0.0
    try:
        for pid in map(int, check_output(["pgrep",name]).split()):
            total += psutil.Process(pid).memory_info().rss
    except Exception as e:
        pass
    return total

Does anybody know why the memory declared by docker is so different?

This is of course a problem for me because the memory limit applied doesn't look respected.

I'm using a Raspberry PI.

Upvotes: 2

Views: 1805

Answers (1)

Edgaras
Edgaras

Reputation: 21

That's because Docker is reporting only RSS from cgroups memory.stats, but you actually need to sum up cache, rss and swap (https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt). More info about that in https://sysrq.tech/posts/docker-misleading-containers-memory-usage/

Upvotes: 2

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