On Wed, Jan 30, 2019 at 03:02:51PM +0100, Martynas Pumputis wrote:

Previously, memory allocated for a map was not accounted. Therefore,
this memory could not be taken into consideration by the cgroups
memory controller.

This patch introduces the "BPF_F_ACCOUNT_MEM" flag which enables
the memory accounting for a map, and it can be set during
the map creation ("BPF_MAP_CREATE") in "map_flags".

When enabled, we account only that amount of memory which is charged
against the "RLIMIT_MEMLOCK" limit.

To validate the change, first we create the memory cgroup "test-map":

    # mkdir /sys/fs/cgroup/memory/test-map

And then we run the following program against the cgroup:

    $ cat test_map.c
    <..>
    int main() {
        usleep(3 * 1000000);
        assert(bpf_create_map(BPF_MAP_TYPE_HASH, 8, 16, 65536, 0) > 0);
        usleep(3 * 1000000);
    }
    # cgexec -g memory:test-map ./test_map &
    # cat /sys/fs/cgroup/memory/test-map/memory{,.kmem}.usage_in_bytes
    397312
    258048

    <after 3 sec the map has been created>

    # bpftool map list
    19: hash  flags 0x0
        key 8B  value 16B  max_entries 65536  memlock 5771264B
    # cat /sys/fs/cgroup/memory/test-map/memory{,.kmem}.usage_in_bytes
    401408
    262144

As we can see, the memory allocated for map is not accounted, as
397312B + 5771264B > 401408B.

Next, we enabled the accounting and re-run the test:

    $ cat test_map.c
    <..>
    int main() {
        usleep(3 * 1000000);
        assert(bpf_create_map(BPF_MAP_TYPE_HASH, 8, 16, 65536, BPF_F_ACCOUNT_MEM) > 0);
        usleep(3 * 1000000);
    }
    # cgexec -g memory:test-map ./test_map &
    # cat /sys/fs/cgroup/memory/test-map/memory{,.kmem}.usage_in_bytes
    450560
    307200

    <after 3 sec the map has been created>

    # bpftool map list
    20: hash  flags 0x80
        key 8B  value 16B  max_entries 65536  memlock 5771264B
    # cat /sys/fs/cgroup/memory/test-map/memory{,.kmem}.usage_in_bytes
    6221824
    6078464

This time, the memory (including kmem) is accounted, as
450560B + 5771264B <= 6221824B

Signed-off-by: Martynas Pumputis <redacted>

...

I think it's better to account this memory by default.
Extra flag during map creation is not needed.
There are nokmem and nosocket memcg boot options.
We can add one more to turn off accounting of bpf map memory.