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Message-ID: <4ed93895-7c73-4dba-9b12-ed6f506d1823@linux.dev>
Date: Fri, 16 Jan 2026 17:49:43 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
cgroups@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>,
hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com,
roman.gushchin@...ux.dev, shakeel.butt@...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
Subject: Re: [PATCH v3 25/30] mm: vmscan: prepare for reparenting traditional
LRU folios
On 2026/1/14 19:32, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@...edance.com>
>
> To resolve the dying memcg issue, we need to reparent LRU folios of child
> memcg to its parent memcg. For traditional LRU list, each lruvec of every
> memcg comprises four LRU lists. Due to the symmetry of the LRU lists, it
> is feasible to transfer the LRU lists from a memcg to its parent memcg
> during the reparenting process.
>
> This commit implements the specific function, which will be used during
> the reparenting process.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Muchun Song <muchun.song@...ux.dev>
With one comment below.
> ---
> include/linux/mmzone.h | 4 ++++
> include/linux/swap.h | 19 +++++++++++++++++++
> mm/swap.c | 37 +++++++++++++++++++++++++++++++++++++
> mm/vmscan.c | 19 -------------------
> 4 files changed, 60 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 6a7db0fee54a3..1014b5a93c09c 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -366,6 +366,10 @@ enum lruvec_flags {
> LRUVEC_NODE_CONGESTED,
> };
>
> +#ifdef CONFIG_MEMCG
> +void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent);
> +#endif /* CONFIG_MEMCG */
Can we move it to swap.h since it is declared in swap.c?
> +
> #endif /* !__GENERATING_BOUNDS_H */
>
> /*
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index e60f45b48e74d..4449d1f371a56 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -636,5 +636,24 @@ static inline bool mem_cgroup_swap_full(struct folio *folio)
> }
> #endif
>
> +/* for_each_managed_zone_pgdat - helper macro to iterate over all managed zones in a pgdat up to
> + * and including the specified highidx
> + * @zone: The current zone in the iterator
> + * @pgdat: The pgdat which node_zones are being iterated
> + * @idx: The index variable
> + * @highidx: The index of the highest zone to return
> + *
> + * This macro iterates through all managed zones up to and including the specified highidx.
> + * The zone iterator enters an invalid state after macro call and must be reinitialized
> + * before it can be used again.
> + */
> +#define for_each_managed_zone_pgdat(zone, pgdat, idx, highidx) \
> + for ((idx) = 0, (zone) = (pgdat)->node_zones; \
> + (idx) <= (highidx); \
> + (idx)++, (zone)++) \
> + if (!managed_zone(zone)) \
> + continue; \
> + else
> +
> #endif /* __KERNEL__*/
> #endif /* _LINUX_SWAP_H */
> diff --git a/mm/swap.c b/mm/swap.c
> index 7e53479ca1732..cb40e80da53cd 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -1090,6 +1090,43 @@ void folio_batch_remove_exceptionals(struct folio_batch *fbatch)
> fbatch->nr = j;
> }
>
> +#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
> +
> static const struct ctl_table swap_sysctl_table[] = {
> {
> .procname = "page-cluster",
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c48ff6e05e004..e738082874878 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -270,25 +270,6 @@ static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
> }
> #endif
>
> -/* for_each_managed_zone_pgdat - helper macro to iterate over all managed zones in a pgdat up to
> - * and including the specified highidx
> - * @zone: The current zone in the iterator
> - * @pgdat: The pgdat which node_zones are being iterated
> - * @idx: The index variable
> - * @highidx: The index of the highest zone to return
> - *
> - * This macro iterates through all managed zones up to and including the specified highidx.
> - * The zone iterator enters an invalid state after macro call and must be reinitialized
> - * before it can be used again.
> - */
> -#define for_each_managed_zone_pgdat(zone, pgdat, idx, highidx) \
> - for ((idx) = 0, (zone) = (pgdat)->node_zones; \
> - (idx) <= (highidx); \
> - (idx)++, (zone)++) \
> - if (!managed_zone(zone)) \
> - continue; \
> - else
> -
> static void set_task_reclaim_state(struct task_struct *task,
> struct reclaim_state *rs)
> {
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