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

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Message-ID: <4d666f52-1494-4a93-b541-b02b46a887e3@linux.dev>
Date: Mon, 19 Jan 2026 11:24:22 +0800
From: Qi Zheng <qi.zheng@...ux.dev>
To: Shakeel Butt <shakeel.butt@...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 1/18/26 9:11 AM, Shakeel Butt wrote:
> 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?

Ah, Because Johannes previously suggested [1] putting it in swap.c:

```
Lastly, vmscan.c is the reclaim policy. Mechanical LRU shuffling like
this is better placed in mm/swap.c.
```

[1]. https://lore.kernel.org/all/aUQCfdnoLQDLoVyg@cmpxchg.org/

> 
>> +#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
>> +
> 
>