Re: [PATCH 2/2] mm/mglru: stop rotating offlined memcgs to the old generation

[Kairui Song]

On Tue, Oct 27, 2026 at 06:06:06PM +0800, T.J. Mercier wrote:
> lru_gen_offline_memcg() moves an offlining memcg to the head of the old
> generation of the memcg LRU (MEMCG_LRU_OLD), so that global reclaim
> visits it first and evicts the folios it left behind.
> 
> Since commit f1cf8d2f36dc ("mm: memcontrol: eliminate the problem of
> dying memory cgroup for LRU folios"), those folios are reparented to the
> parent before lru_gen_offline_memcg() runs, and nothing can be added
> back to the offlined memcg's lruvec afterwards. Putting an empty
> offlined memcg at the head of the old generation no longer serves any
> purpose and only delays reclaim from the memcgs that still have memory
> due to additional shrink_many() iteration.
> 
> Remove lru_gen_offline_memcg(), so that an offlined memcg is rotated
> like any other memcg below the reclaimable size threshold until
> lru_gen_release_memcg() takes it off the memcg LRU. MEMCG_LRU_OLD has no
> other user, so remove the op and update the memcg LRU comment as well.
> 
> Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
> ---
>  Documentation/mm/multigen_lru.rst |  4 +---
>  include/linux/mmzone.h            | 14 +++-----------
>  mm/memcontrol.c                   |  1 -
>  mm/vmscan.c                       | 20 +-------------------
>  4 files changed, 5 insertions(+), 34 deletions(-)
> 

...

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 636152d8c94d..45a2c1021f4f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4538,7 +4538,6 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
>  enum {
>  	MEMCG_LRU_NOP,
>  	MEMCG_LRU_TAIL,
> -	MEMCG_LRU_OLD,
>  	MEMCG_LRU_YOUNG,
>  };

I think there could be other usage of this LRU_OLD macro, but indeed
offline is the only user currently, removing it is cleaner.

And everything looks good to me, thanks!

Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>