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SubjectRe: [PATCH 4/7] cgroup: rstat: support cgroup1
On Thu 04-02-21 11:01:30, Johannes Weiner wrote:
> On Thu, Feb 04, 2021 at 02:39:25PM +0100, Michal Hocko wrote:
> > On Tue 02-02-21 13:47:43, Johannes Weiner wrote:
> > > Rstat currently only supports the default hierarchy in cgroup2. In
> > > order to replace memcg's private stats infrastructure - used in both
> > > cgroup1 and cgroup2 - with rstat, the latter needs to support cgroup1.
> > >
> > > The initialization and destruction callbacks for regular cgroups are
> > > already in place. Remove the cgroup_on_dfl() guards to handle cgroup1.
> > >
> > > The initialization of the root cgroup is currently hardcoded to only
> > > handle cgrp_dfl_root.cgrp. Move those callbacks to cgroup_setup_root()
> > > and cgroup_destroy_root() to handle the default root as well as the
> > > various cgroup1 roots we may set up during mounting.
> > >
> > > The linking of css to cgroups happens in code shared between cgroup1
> > > and cgroup2 as well. Simply remove the cgroup_on_dfl() guard.
> > >
> > > Linkage of the root css to the root cgroup is a bit trickier: per
> > > default, the root css of a subsystem controller belongs to the default
> > > hierarchy (i.e. the cgroup2 root). When a controller is mounted in its
> > > cgroup1 version, the root css is stolen and moved to the cgroup1 root;
> > > on unmount, the css moves back to the default hierarchy. Annotate
> > > rebind_subsystems() to move the root css linkage along between roots.
> >
> > I am not familiar with rstat API and from this patch it is not really
> > clear to me how does it deal with memcg v1 use_hierarchy oddness.
>
> That's gone, right?
>
> static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
> struct cftype *cft, u64 val)
> {
> if (val == 1)
> return 0;
>
> pr_warn_once("Non-hierarchical mode is deprecated. "
> "Please report your usecase to linux-mm@kvack.org if you "
> "depend on this functionality.\n");
>
> return -EINVAL;
> }

Ohh, right! I have completely forgot it hit the Linus tree.

--
Michal Hocko
SUSE Labs

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