linux-kernel - Re: [PATCH RFC 27/28] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios

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Message-ID: <aCxnFg0VSpd7g_Ju@hyeyoo>
Date: Tue, 20 May 2025 20:27:18 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Muchun Song <songmuchun@...edance.com>
Cc: hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
        shakeel.butt@...ux.dev, muchun.song@...ux.dev,
        akpm@...ux-foundation.org, david@...morbit.com,
        zhengqi.arch@...edance.com, yosry.ahmed@...ux.dev, nphamcs@...il.com,
        chengming.zhou@...ux.dev, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        hamzamahfooz@...ux.microsoft.com, apais@...ux.microsoft.com
Subject: Re: [PATCH RFC 27/28] mm: memcontrol: eliminate the problem of dying
 memory cgroup for LRU folios

On Tue, Apr 15, 2025 at 10:45:31AM +0800, Muchun Song wrote:
> Pagecache pages are charged at allocation time and hold a reference
> to the original memory cgroup until reclaimed. Depending on memory
> pressure, page sharing patterns between different cgroups and cgroup
> creation/destruction rates, many dying memory cgroups can be pinned
> by pagecache pages, reducing page reclaim efficiency and wasting
> memory. Converting LRU folios and most other raw memory cgroup pins
> to the object cgroup direction can fix this long-living problem.
> 
> Finally, folio->memcg_data of LRU folios and kmem folios will always
> point to an object cgroup pointer. The folio->memcg_data of slab
> folios will point to an vector of object cgroups.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  include/linux/memcontrol.h |  78 +++++--------
>  mm/huge_memory.c           |  33 ++++++
>  mm/memcontrol-v1.c         |  15 ++-
>  mm/memcontrol.c            | 228 +++++++++++++++++++++++++------------
>  4 files changed, 222 insertions(+), 132 deletions(-)

[...]

> +static void lruvec_reparent_lru(struct lruvec *src, struct lruvec *dst,
> +				enum lru_list lru)
> +{
> +	int zid;
> +	struct mem_cgroup_per_node *mz_src, *mz_dst;
> +
> +	mz_src = container_of(src, struct mem_cgroup_per_node, lruvec);
> +	mz_dst = container_of(dst, struct mem_cgroup_per_node, lruvec);
> +
> +	if (lru != LRU_UNEVICTABLE)
> +		list_splice_tail_init(&src->lists[lru], &dst->lists[lru]);
> +
> +	for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> +		mz_dst->lru_zone_size[zid][lru] += mz_src->lru_zone_size[zid][lru];
> +		mz_src->lru_zone_size[zid][lru] = 0;
> +	}
> +}

I think this function should also update memcg and lruvec stats of
parent memcg? Or is it intentional?

-- 
Cheers,
Harry / Hyeonggon