Re: [PATCH 1/4 v2] cgroup: move cgroup_rstat from cgroup to cgroup_subsys_state

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Feb 27, 2025 at 01:55:40PM -0800, inwardvessel wrote:
> From: JP Kobryn <inwardvessel@gmail.com>
> 
> Each cgroup owns rstat pointers. This means that a tree of pending rstat
> updates can contain changes from different subsystems. Because of this
> arrangement, when one subsystem is flushed via the public api
> cgroup_rstat_flushed(), all other subsystems with pending updates will
> also be flushed. Remove the rstat pointers from the cgroup and instead
> give them to each cgroup_subsys_state. Separate rstat trees will now
> exist for each unique subsystem. This separation allows for subsystems
> to make updates and flushes without the side effects of other
> subsystems. i.e. flushing the cpu stats does not cause the memory stats
> to be flushed and vice versa. The change in pointer ownership from
> cgroup to cgroup_subsys_state allows for direct flushing of the css, so
> the rcu list management entities and operations previously tied to the
> cgroup which were used for managing a list of subsystem states with
> pending flushes are removed. In terms of client code, public api calls
> were changed to now accept a reference to the cgroup_subsys_state so
> that when flushing or updating, a specific subsystem is associated with
> the call.
> 
> Signed-off-by: JP Kobryn <inwardvessel@gmail.com>

Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>

One nit: add couple of lines in commit message  on why removing the
padding from struct cgroup is fine. Most probably the reason to add the
padding is not valid anymore.