linux-kernel - Re: [PATCH] mm: Restore per-memcg proactive reclaim with !CONFIG

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Message-ID: <aW3kgrVhWQEyGM-G@tiehlicka>
Date: Mon, 19 Jan 2026 09:00:02 +0100
From: Michal Hocko <mhocko@...e.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Davidlohr Bueso <dave@...olabs.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm: Restore per-memcg proactive reclaim with !CONFIG_NUMA

On Fri 16-01-26 20:52:47, Yosry Ahmed wrote:
> Commit 2b7226af730c ("mm/memcg: make memory.reclaim interface generic")
> moved proactive reclaim logic from memory.reclaim handler to a generic
> user_proactive_reclaim() helper to be used for per-node proactive
> reclaim.
> 
> However, user_proactive_reclaim() was only defined under CONFIG_NUMA,
> with a stub always returning 0 otherwise. This broke memory.reclaim on
> !CONFIG_NUMA configs, causing it to report success without actually
> attempting reclaim.
> 
> Move the definition of user_proactive_reclaim() outside CONFIG_NUMA, and
> instead define a stub for __node_reclaim() in the !CONFIG_NUMA case.
> __node_reclaim() is only called from user_proactive_reclaim() when a
> write is made to sys/devices/system/node/nodeX/reclaim, which is only
> defined with CONFIG_NUMA.
> 
> Fixes: 2b7226af730c ("mm/memcg: make memory.reclaim interface generic")
> Cc: stable@...r.kernel.org
> Signed-off-by: Yosry Ahmed <yosry.ahmed@...ux.dev>

Ouch.
Acked-by: Michal Hocko <mhocko@...e.com>
Thanks for catching that up.

> ---
>  mm/internal.h |  8 --------
>  mm/vmscan.c   | 13 +++++++++++--
>  2 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index 33eb0224f461..9508dbaf47cd 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -615,16 +615,8 @@ extern unsigned long highest_memmap_pfn;
>  bool folio_isolate_lru(struct folio *folio);
>  void folio_putback_lru(struct folio *folio);
>  extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
> -#ifdef CONFIG_NUMA
>  int user_proactive_reclaim(char *buf,
>  			   struct mem_cgroup *memcg, pg_data_t *pgdat);
> -#else
> -static inline int user_proactive_reclaim(char *buf,
> -			   struct mem_cgroup *memcg, pg_data_t *pgdat)
> -{
> -	return 0;
> -}
> -#endif
>  
>  /*
>   * in mm/rmap.c:
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7b28018ac995..d9918f24dea0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -7849,6 +7849,17 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
>  	return ret;
>  }
>  
> +#else
> +
> +static unsigned long __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask,
> +				    unsigned long nr_pages,
> +				    struct scan_control *sc)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
>  enum {
>  	MEMORY_RECLAIM_SWAPPINESS = 0,
>  	MEMORY_RECLAIM_SWAPPINESS_MAX,
> @@ -7956,8 +7967,6 @@ int user_proactive_reclaim(char *buf,
>  	return 0;
>  }
>  
> -#endif
> -
>  /**
>   * check_move_unevictable_folios - Move evictable folios to appropriate zone
>   * lru list
> -- 
> 2.52.0.457.g6b5491de43-goog

-- 
Michal Hocko
SUSE Labs