Re: [PATCH 1/2] memcg: move mem_cgroup_swappiness to memcontrol.h

[Barry Song]

On Sat, Jul 11, 2026 at 5:12 PM Ridong Chen <ridong.chen@xxxxxxxxx> wrote:
>
> From: Ridong Chen <chenridong@xxxxxxxxxx>
>
> The per-memcg swappiness knob is v1-only; v2 always uses global
> vm_swappiness and ignores the per-cgroup field.
>
> Guard memcg->swappiness with CONFIG_MEMCG_V1, and move the helper
> to memcontrol.h where it belongs.
>
> No functional change for v1; v2-only kernels drop the unused field.
>
> Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Barry Song <baohua@xxxxxxxxxx>

With some nits.

> ---
[...]
>         struct mem_cgroup_per_node *nodeinfo[];
> @@ -365,6 +366,9 @@ enum objext_flags {
>
>  #define OBJEXTS_FLAGS_MASK (__NR_OBJEXTS_FLAGS - 1)
>
> +/* Defined in mm/vmscan.c; used by mem_cgroup_swappiness(). */
> +extern int vm_swappiness;

This is a bit unusual. I'm not sure whether mm/swap.h would be
a more appropriate place for this.

Thanks
Barry