Re: [PATCH] memcg: hugetlbfs basic usage accounting

[Johannes Weiner]

On Tue, Nov 14, 2017 at 05:24:29PM +0000, Roman Gushchin wrote:
> This patch implements basic accounting of memory consumption
> by hugetlbfs pages for cgroup v2 memory controller.
> 
> Cgroup v2 memory controller lacks any visibility into the
> hugetlbfs memory consumption. Cgroup v1 implemented a separate
> hugetlbfs controller, which provided such stats, and also
> provided some control abilities. Although porting of the
> hugetlbfs controller to cgroup v2 is arguable a good idea and
> is outside of scope of this patch, it's very useful to have
> basic stats provided by memory.stat.
> 
> As hugetlbfs memory can easily represent a big portion of total
> memory, it's important to understand who (which memcg/container)
> is using it.

I'm not really buying this argument.

Hugetlb setups tend to be static configurations that require intimate
coordination between booting the kernel with a hugetlb reservation and
precisely setting up the application(s).

In the few cases where you need introspection, you can check the the
HugetlbPages entry in /proc/<pid>/status. The minor convenience
provided by adding an aggregate cgroup counter IMO doesn't outweigh
the weirdness of listing a type of resource in memory.stat that isn't
otherwise acknowledged or controllable as memory.