Re: [PATCH v6 1/4] mm: swap: introduce swap tier infrastructure

[Baoquan He]

On 04/21/26 at 02:53pm, Youngjun Park wrote:
> This patch introduces the "Swap tier" concept, which serves as an
> abstraction layer for managing swap devices based on their performance
> characteristics (e.g., NVMe, HDD, Network swap).
> 
> Swap tiers are user-named groups representing priority ranges.
> Tier names must consist of alphanumeric characters and underscores.
> These tiers collectively cover the entire priority space from -1
> (`DEF_SWAP_PRIO`) to `SHRT_MAX`.
> 
> To configure tiers, a new sysfs interface is exposed at
> /sys/kernel/mm/swap/tiers. The input parser evaluates commands from
> left to right and supports batch input, allowing users to add or remove
> multiple tiers in a single write operation.
> 
> Tier management enforces continuous priority ranges anchored by start
> priorities. Operations trigger range splitting or merging, but overwriting
> start priorities is forbidden. Merging expands lower tiers upwards to
> preserve configured start priorities, except when removing `DEF_SWAP_PRIO`,
> which merges downwards.
> 
> Suggested-by: Chris Li <chrisl@xxxxxxxxxx>
> Signed-off-by: Youngjun Park <youngjun.park@xxxxxxx>

This looks good to me.

Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>

While there's only one tiny concern, please see the inline comment.

> diff --git a/mm/swap_tier.c b/mm/swap_tier.c
> new file mode 100644
> index 000000000000..9490e891c5fe
> --- /dev/null
> +++ b/mm/swap_tier.c
> @@ -0,0 +1,302 @@
......
> +/*
> + * Naming Convention:
> + *   swap_tiers_*() - Public/exported functions
> + *   swap_tier_*()  - Private/internal functions
> + */
> +
> +static bool swap_tier_is_active(void)
> +{
> +	return !list_empty(&swap_tier_active_list) ? true : false;

The above line seems like generated by AI. Whatever else I have seen is
"return !list_empty(&swap_tier_active_list);" which is enough.

> +}
> +
...snip...