Re: [DISCUSSION] proposed mctl() API

[Tejun Heo <tj@kernel.org>]

Hello,

On Thu, Jun 05, 2025 at 08:31:56AM -0400, Johannes Weiner wrote:
> On Wed, Jun 04, 2025 at 08:19:28AM -0400, Johannes Weiner wrote:
> > On Fri, May 30, 2025 at 12:31:35PM +0200, Vlastimil Babka wrote:
...
> > > I've just read the previous threads about Barry's proposal and if doing this
> > > always isn't feasible, I'm wondering if memcg would be a better interface to
> > > opt-in for this kind of behavior than both prctl or mctl. I think at least
> > > conceptually it fits what memcg is doing? The question is if the
> > > implementation would be feasible, and if android puts apps in separate memcgs...
> > 
> > CCing Tejun.
> > 
> > Cgroups has been trying to resist flag settings like these. The cgroup
> > tree is a nested hierarchical structure designed for dividing up
> > system resources. But flag properties don't have natural inheritance
> > rules. What does it mean if the parent group says one thing and the
> > child says another? Which one has precedence?
> > 
> > Hence the proposal to make it a per-process property that propagates
> > through fork() and exec(). This also enables the container usecase (by
> > setting the flag in the container launching process), without there
> > being any confusion what the *effective* setting for any given process
> > in the system is.

+1. If something can work as something which gets inherited through the
process hierarchy, that's usually the better choice than making it a cgroup
property. There isn't much to be gained by making them cgroup properties
especially given that cgroup hierarchy, in most systems at this point, is a
degenerated process hierarchy.

Thanks.

-- 
tejun