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SubjectRe: [PATCH 1/2] cgroup: Add generation number with cgroup id
Hi Tejun,

On Fri, Oct 25, 2019 at 2:44 AM Tejun Heo <tj@kernel.org> wrote:
> On Wed, Oct 16, 2019 at 09:50:18PM +0900, Namhyung Kim wrote:
> > Later 64 bit system can have a simpler implementation with a single 64
> > bit sequence number and a RB tree. But it'll need to grab a spinlock
> > during lookup. I'm not entirely sure it's ok, so I left it as is.
>
> Any chance I can persuade you into making this conversion? idr is
> exactly the wrong data structure to use for cyclic allocations. We've
> been doing it mostly for historical reasons but I really hope we can
> move away from it. These lookups aren't in super hot paths and doing
> locked lookups should be fine.

As you know, it entails change in kernfs id and its users.
And I really want to finish the perf cgroup sampling work first.
Can I work on this after the perf work is done?

>
> > /*
> > * A cgroup_root represents the root of a cgroup hierarchy, and may be
> > * associated with a kernfs_root to form an active hierarchy. This is
> > @@ -521,7 +529,7 @@ struct cgroup_root {
> > unsigned int flags;
> >
> > /* IDs for cgroups in this hierarchy */
> > - struct idr cgroup_idr;
> > + struct cgroup_idr cgroup_idr;
>
> Given that there's cgroup->self css, can we get rid of the above?

I don't follow. Do you want to remove cgroup_idr and share the
css_idr for cgroup id?

Thanks
Namhyung

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