linux-kernel - Re: [PATCH] mm/mglru: Update MG-LRU proactive reclaim statistics only to memcg

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Message-ID: <z3n3dfpgrctgf3mlkqydmos2svh353v3qzd22n4g3iygji6rsr@4l4zgkrl5w35>
Date: Thu, 17 Jul 2025 12:47:32 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Hao Jia <jiahao.kernel@...il.com>
Cc: akpm@...ux-foundation.org, yuzhao@...gle.com, yuanchu@...gle.com, 
	mhocko@...nel.org, lorenzo.stoakes@...cle.com, kinseyho@...gle.com, 
	hannes@...xchg.org, gthelen@...gle.com, david@...hat.com, axelrasmussen@...gle.com, 
	zhengqi.arch@...edance.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Hao Jia <jiahao1@...iang.com>
Subject: Re: [PATCH] mm/mglru: Update MG-LRU proactive reclaim statistics
 only to memcg

Hi Hao,

On Thu, Jul 17, 2025 at 04:28:45PM +0800, Hao Jia wrote:
> From: Hao Jia <jiahao1@...iang.com>
> 
> Users can use /sys/kernel/debug/lru_gen to trigger proactive memory reclaim
> of a specified memcg.

Are you using this interface for proactively reclaiming a specific
memcg? I see run_cmd() using mem_cgroup_from_id() to get memcg from a
given id but I don't think we expose ids from mem_cgroup_ids to the
userspace. Usually we use cgroup_id which is just an inode number for
the cgroup folder. I wonder if the current users of this interface are
providing memcg id.

> Currently, statistics such as pgrefill, pgscan and
> pgsteal will be updated to the /proc/vmstat system memory statistics.
> 
> This will confuse some system memory pressure monitoring tools, making
> it difficult to determine whether pgscan and pgsteal are caused by
> system-level pressure or by proactive memory reclaim of some specific
> memory cgroup.
> 
> Therefore, make this interface behave similarly to memory.reclaim.
> Update proactive memory reclaim statistics only to its memory cgroup.
> 
> Signed-off-by: Hao Jia <jiahao1@...iang.com>

The patch looks fine though.

> ---
>  mm/vmscan.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f8dfd2864bbf..bc92ec338065 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -5545,6 +5545,7 @@ static int run_cmd(char cmd, int memcg_id, int nid, unsigned long seq,
>  	if (memcg_id != mem_cgroup_id(memcg))
>  		goto done;
>  
> +	sc->target_mem_cgroup = memcg;
>  	lruvec = get_lruvec(memcg, nid);
>  
>  	if (swappiness < MIN_SWAPPINESS)
> @@ -5581,6 +5582,7 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
>  		.may_swap = true,
>  		.reclaim_idx = MAX_NR_ZONES - 1,
>  		.gfp_mask = GFP_KERNEL,
> +		.proactive = true,
>  	};
>  
>  	buf = kvmalloc(len + 1, GFP_KERNEL);
> -- 
> 2.34.1
>