Re: Question on damon_sysfs_memcg_path_to_id() path resolution

[SJ Park <sj@kernel.org>]

On Sat, 18 Jul 2026 16:40:51 +0800 Song Hu <husong@kylinos.cn> wrote:

> Hi,
> 
> Sorry for the late reply.

No worry!

[...]
> > I find the current behavior might be tedious if the user runs DAMON inside
> > cgroups.  Finding the absolute cgroup path inside containers might be
> > challenging.  If that's the case, I'm up to change or extend the behaviors.
> >
> > If this is only for making the code easier to maintain, I don't really feel
> > like it deserves the behavioral changes, to be honest.
> I looked into the container case more carefully and I'm no longer sure
> it justifies the change.
> 
> DAMON sysfs is root-only (state is 0600 under /sys/kernel/mm/damon), so
> whoever configures a scheme is effectively a host-level operator.  That
> operator can obtain the absolute cgroup path directly (e.g. from
> /proc/<pid>/cgroup), and the usage docs already show host-absolute
> paths.  A process able to write host DAMON sysfs from inside a non-init
> cgroup namespace is a privileged host-admin case, not really a "DAMON
> inside a container" user.  So I think the namespace-relative benefit is
> marginal at best.
> 
> Given that, and your point that maintainability alone isn't worth a
> behavioral change, I'll leave damon_sysfs_memcg_path_to_id() as-is.

Makes sense.

> 
> Thanks for thinking it through with me -- and for the cgroup_get_from_path pointer.

You're welcome.  I liked this dicsussion.  Looking forward to the next one!


Thanks,
SJ

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