linux-kernel - Re: [PATCH v3 25/30] mm: vmscan: prepare for reparenting traditional LRU folios

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Message-ID: <6hlbucao3tfp2bxyaekcrvhqclji4hyhq4wen4sccc2qcdr6x2@rtmqrfwfsy4s>
Date: Sat, 17 Jan 2026 17:11:16 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com, 
	roman.gushchin@...ux.dev, muchun.song@...ux.dev, david@...nel.org, 
	lorenzo.stoakes@...cle.com, ziy@...dia.com, harry.yoo@...cle.com, yosry.ahmed@...ux.dev, 
	imran.f.khan@...cle.com, kamalesh.babulal@...cle.com, axelrasmussen@...gle.com, 
	yuanchu@...gle.com, weixugc@...gle.com, chenridong@...weicloud.com, mkoutny@...e.com, 
	akpm@...ux-foundation.org, hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com, 
	lance.yang@...ux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v3 25/30] mm: vmscan: prepare for reparenting traditional
 LRU folios

On Wed, Jan 14, 2026 at 07:32:52PM +0800, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@...edance.com>
> 
[...]
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -1090,6 +1090,43 @@ void folio_batch_remove_exceptionals(struct folio_batch *fbatch)
>  	fbatch->nr = j;
>  }
>  

Why not define the following two functions in memcontrol.c?

> +#ifdef CONFIG_MEMCG
> +static void lruvec_reparent_lru(struct lruvec *child_lruvec,
> +				struct lruvec *parent_lruvec,
> +				enum lru_list lru, int nid)
> +{
> +	int zid;
> +	struct zone *zone;
> +
> +	if (lru != LRU_UNEVICTABLE)
> +		list_splice_tail_init(&child_lruvec->lists[lru], &parent_lruvec->lists[lru]);
> +
> +	for_each_managed_zone_pgdat(zone, NODE_DATA(nid), zid, MAX_NR_ZONES - 1) {
> +		unsigned long size = mem_cgroup_get_zone_lru_size(child_lruvec, lru, zid);
> +
> +		mem_cgroup_update_lru_size(parent_lruvec, lru, zid, size);
> +	}
> +}
> +
> +void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent)
> +{
> +	int nid;
> +
> +	for_each_node(nid) {
> +		enum lru_list lru;
> +		struct lruvec *child_lruvec, *parent_lruvec;
> +
> +		child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
> +		parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid));
> +		parent_lruvec->anon_cost += child_lruvec->anon_cost;
> +		parent_lruvec->file_cost += child_lruvec->file_cost;
> +
> +		for_each_lru(lru)
> +			lruvec_reparent_lru(child_lruvec, parent_lruvec, lru, nid);
> +	}
> +}
> +#endif
> +