Expose new metrics for memory usage in the container.

[fcuny]

The metric "mem_kmem_usage_bytes" is the total kernel memory usage by
processes in the cgroup in bytes.

The metric "mem_kmem_tcp_usage_bytes" is the total memory usage for TCP
buffers in bytes.

[jieyu]

I don't think we turn on kmem accounting yet in Mesos containerizer.

I remember in old kernels, you need to set kmem.limit_in_bytes once to enable kmem accounting. I am not sure about the new kernel behavior.

Also, we need to be careful on bugs like this on old kernels if we turn on kmem accounting
opencontainers/runc#1725

[fcuny]

We've been running with this patch at Twitter since February and we're getting kmem metrics.

The mentioned bug is interesting, we've only been running with 4.9 and later.

[jieyu]

I am not sure if the kernel behavior has changed or not in newer kernels. For example:
https://github.com/opencontainers/runc/blob/7139b61f7fdb904d0acb8db825709aa8d2d2ef36/libcontainer/cgroups/fs/memory.go#L70

You'll have to write memory.kmem.limit_in_bytes to enable kmem accounting

So if kmem accounting is not enabled, i don't know what will happen if you read the data from memory.kmem.usage_in_bytes. Let me do some testing on my CentOS 7 default kernel (3.10)

[jieyu]

Looks like on CentOS 7 (3.10.0-693.5.2.el7.x86_64). If kmem accounting is not enabled, the memory.kmem.limit_in_bytes will always show 0. And reading memory.kmem.slabinfo will give Input/output error

I think we should probably add an agent flag to control the enabling of kmem accounting feature, and only report stats if kmem accounting is enabled.

[fcuny]

That sounds reasonable. I'll get to update the review with this.

Should I move the review to reviewboard or keep iterating here ?

[jieyu]

@fcuny We prefer reviewboard for non trivial changes.

[greggomann]

@fcuny were you going to continue this work on ReviewBoard?