Re: [PATCH v2 3/3] mm/page_owner: Dump memcg information

[Roman Gushchin]

On Wed, Feb 02, 2022 at 09:57:18AM +0100, Michal Hocko wrote:
> On Tue 01-02-22 11:41:19, Waiman Long wrote:
> > 
> > On 2/1/22 05:49, Michal Hocko wrote:
> [...]
> > > Could you be more specific? Offlined memcgs are still part of the
> > > hierarchy IIRC. So it shouldn't be much more than iterating the whole
> > > cgroup tree and collect interesting data about dead cgroups.
> > 
> > What I mean is that without piggybacking on top of page_owner, we will to
> > add a lot more code to collect and display those information which may have
> > some overhead of its own.
> 
> Yes, there is nothing like a free lunch. Page owner is certainly a tool
> that can be used. My main concern is that this tool doesn't really
> scale on large machines with a lots of memory. It will provide a very
> detailed information but I am not sure this is particularly helpful to
> most admins (why should people process tons of allocation backtraces in
> the first place). Wouldn't it be sufficient to have per dead memcg stats
> to see where the memory sits?
> 
> Accumulated offline memcgs is something that bothers more people and I
> am really wondering whether we can do more for those people to evaluate
> the current state.

Cgroup v2 has corresponding counters for years. Or do you mean something different?