Re: [PATCH mm-unstable v1 6/8] mm: multi-gen LRU: per-node lru_gen_folio lists

[Hillf Danton <hdanton@sina.com>]

On 1 Dec 2022 15:39:22 -0700 Yu Zhao <yuzhao@google.com>
> @@ -477,6 +477,16 @@ static void mem_cgroup_update_tree(struct mem_cgroup *memcg, int nid)
>  	struct mem_cgroup_per_node *mz;
>  	struct mem_cgroup_tree_per_node *mctz;
>  
> +	if (lru_gen_enabled()) {
> +		struct lruvec *lruvec = &memcg->nodeinfo[nid]->lruvec;
> +
> +		/* see the comment on MEMCG_NR_GENS */
> +		if (soft_limit_excess(memcg) && lru_gen_memcg_seg(lruvec) != MEMCG_LRU_HEAD)
> +			lru_gen_rotate_memcg(lruvec, MEMCG_LRU_HEAD);
> +
> +		return;

The heuristic of rotation is so weak a signal in the background noise
produced by prandom_u32_max(MEMCG_NR_BINS), wonder if mcgroup lru works
no fine without it.

> +	}
> +
>  	mctz = soft_limit_tree.rb_tree_per_node[nid];
>  	if (!mctz)
>  		return;
> @@ -3526,6 +3536,9 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
>  	struct mem_cgroup_tree_per_node *mctz;
>  	unsigned long excess;
>  
> +	if (lru_gen_enabled())
> +		return 0;
> +
>  	if (order > 0)
>  		return 0;
>