Re: [PATCH] mm: vmscan: skip the file folios in proactive reclaim if swappiness is MAX

[Yosry Ahmed <yosry.ahmed@linux.dev>]

On Wed, Mar 12, 2025 at 05:43:37PM +0800, Zhongkun He wrote:
> With this patch 'commit <68cd9050d871> ("mm: add swappiness= arg to
> memory.reclaim")', we can submit an additional swappiness=<val> argument
> to memory.reclaim. It is very useful because we can dynamically adjust
> the reclamation ratio based on the anonymous folios and file folios of
> each cgroup. For example,when swappiness is set to 0, we only reclaim
> from file pages.
> 
> However,we have also encountered a new issue: when swappiness is set to
> the MAX_SWAPPINESS, it may still only reclaim file folios. This is due
> to the knob of cache_trim_mode, which depends solely on the ratio of
> inactive folios, regardless of whether there are a large number of cold
> folios in anonymous folio list.
> 
> So, we hope to add a new control logic where proactive memory reclaim only
> reclaims from anonymous folios when swappiness is set to MAX_SWAPPINESS.
> For example, something like this:
> 
> echo "2M swappiness=200" > /sys/fs/cgroup/memory.reclaim
> 
> will perform reclaim on the rootcg with a swappiness setting of 200 (max
> swappiness) regardless of the file folios. Users have a more comprehensive
> view of the application's memory distribution because there are many
> metrics available.
> 
> With this patch, the swappiness argument of memory.reclaim has a more
> precise semantics: 0 means reclaiming only from file pages, while 200
> means reclaiming just from anonymous pages.
> 
> Signed-off-by: Zhongkun He <hezhongkun.hzk@bytedance.com>

Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>

> ---
>  mm/vmscan.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c767d71c43d7..f4312b41e0e0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2438,6 +2438,16 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  		goto out;
>  	}
>  
> +	/*
> +	 * Do not bother scanning file folios if the memory reclaim
> +	 * invoked by userspace through memory.reclaim and the
> +	 * swappiness is MAX_SWAPPINESS.
> +	 */
> +	if (sc->proactive && (swappiness == MAX_SWAPPINESS)) {
> +		scan_balance = SCAN_ANON;
> +		goto out;
> +	}
> +
>  	/*
>  	 * Do not apply any pressure balancing cleverness when the
>  	 * system is close to OOM, scan both anon and file equally
> -- 
> 2.39.5
> 
>