Re: [PATCH v5 update 30/32] mm: memcontrol: convert objcg to be per-memcg per-node type

[Shakeel Butt]

On Wed, Feb 25, 2026 at 05:44:56PM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> 
> Convert objcg to be per-memcg per-node type, so that when reparent LRU
> folios later, we can hold the lru lock at the node level, thus avoiding
> holding too many lru locks at once.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> ---
> changlog:
>  - fix a missing root_obj_cgroup conversion and completely delete
>    root_obj_cgroup.
> 
>  include/linux/memcontrol.h | 23 +++++------
>  include/linux/sched.h      |  2 +-
>  mm/memcontrol.c            | 79 +++++++++++++++++++++++---------------
>  3 files changed, 62 insertions(+), 42 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 45d911dd903e7..6e11552a90618 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -116,6 +116,16 @@ struct mem_cgroup_per_node {
>  	unsigned long		lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
>  	struct mem_cgroup_reclaim_iter	iter;
>  
> +	/*
> +	 * objcg is wiped out as a part of the objcg repaprenting process.
> +	 * orig_objcg preserves a pointer (and a reference) to the original
> +	 * objcg until the end of live of memcg.
> +	 */
> +	struct obj_cgroup __rcu	*objcg;
> +	struct obj_cgroup	*orig_objcg;

The layout of struct mem_cgroup_per_node is very performance sensitive. Please
couple of performance benchmarks after rearranging the fields particularly the
above two pointers together at the start of the struct.

Otherwise:

Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>