linux-kernel - Re: [PATCH 2/4] mm/memcg: make memory.reclaim interface generic

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Message-ID: <87bjpjshn7.fsf@linux.dev>
Date: Wed, 16 Jul 2025 18:58:04 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: akpm@...ux-foundation.org,  mhocko@...nel.org,  hannes@...xchg.org,
  shakeel.butt@...ux.dev,  yosryahmed@...gle.com,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mm/memcg: make memory.reclaim interface generic

Davidlohr Bueso <dave@...olabs.net> writes:

> This adds a general call for both parsing as well as the
> common reclaim semantics. memcg is still the only user and
> no change in semantics.
>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> ---
>  mm/internal.h   |  2 +
>  mm/memcontrol.c | 77 ++------------------------------------
>  mm/vmscan.c     | 98 +++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 104 insertions(+), 73 deletions(-)
> ...
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c13c01eb0b42..63ddec550c3b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -57,6 +57,7 @@
>  #include <linux/rculist_nulls.h>
>  #include <linux/random.h>
>  #include <linux/mmu_notifier.h>
> +#include <linux/parser.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -6714,6 +6715,15 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
>  
>  	return nr_reclaimed;
>  }
> +#else
> +unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> +					   unsigned long nr_pages,
> +					   gfp_t gfp_mask,
> +					   unsigned int reclaim_options,
> +					   int *swappiness)
> +{
> +	return 0;
> +}
>  #endif
>  
>  static void kswapd_age_node(struct pglist_data *pgdat, struct scan_control *sc)
> @@ -7708,6 +7718,94 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
>  
>  	return ret;
>  }
> +
> +enum {
> +	MEMORY_RECLAIM_SWAPPINESS = 0,
> +	MEMORY_RECLAIM_SWAPPINESS_MAX,
> +	MEMORY_RECLAIM_NULL,
> +};
> +static const match_table_t tokens = {
> +	{ MEMORY_RECLAIM_SWAPPINESS, "swappiness=%d"},
> +	{ MEMORY_RECLAIM_SWAPPINESS_MAX, "swappiness=max"},
> +	{ MEMORY_RECLAIM_NULL, NULL },
> +};
> +
> +int user_proactive_reclaim(char *buf, struct mem_cgroup *memcg, pg_data_t *pgdat)
> +{
> +	unsigned int nr_retries = MAX_RECLAIM_RETRIES;
> +	unsigned long nr_to_reclaim, nr_reclaimed = 0;
> +	int swappiness = -1;
> +	char *old_buf, *start;
> +	substring_t args[MAX_OPT_ARGS];
> +
> +	if (!buf || (!memcg && !pgdat))
> +		return -EINVAL;
> +
> +	buf = strstrip(buf);
> +
> +	old_buf = buf;
> +	nr_to_reclaim = memparse(buf, &buf) / PAGE_SIZE;
> +	if (buf == old_buf)
> +		return -EINVAL;
> +
> +	buf = strstrip(buf);

To be honest, not a big fan of this refactoring. Effectively parts of
the memcg user interface are moved into mm/vmscan.c. I get that you want
to use the exact same interface somewhere else, but still...

Is it possible to keep it in mm/memcontrol.c?
Also maybe split the actual reclaim mechanism and user's input parsing?

Thanks