Re: [PATCH RFC 1/3] cgroup: list all subsystem states in debugfs files

[Johannes Weiner]

On Mon, Aug 13, 2018 at 06:48:42AM -0700, Tejun Heo wrote:
> Hello, Konstantin.
> 
> On Mon, Aug 13, 2018 at 09:58:05AM +0300, Konstantin Khlebnikov wrote:
> > After removing cgroup subsystem state could leak or live in background
> > forever because it is pinned by some reference. For example memory cgroup
> > could be pinned by pages in cache or tmpfs.
> > 
> > This patch adds common debugfs interface for listing basic state for each
> > controller. Controller could define callback for dumping own attributes.
> > 
> > In file /sys/kernel/debug/cgroup/<controller> each line shows state in
> > format: <common_attr>=<value>... [-- <controller_attr>=<value>... ]
> 
> Seems pretty useful to me.  Roman, Johannes, what do you guys think?

Generally I like the idea of having more introspection into offlined
cgroups, but I wonder if having only memory= and swap= could be a
little too terse to track down what exactly is pinning the groups.

Roman has more experience debugging these pileups, but it seems to me
that unless we add a breakdown off memory, and maybe make slabinfo
available for these groups, that in practice this might not provide
that much more insight than per-cgroup stat counters of dead children.