Re: [PATCH v4 4/5] zsmalloc: Add ops fields to zs_pool to store evict handlers

[Minchan Kim]

On Thu, Nov 17, 2022 at 08:38:38AM -0800, Nhat Pham wrote:
> This adds fields to zs_pool to store evict handlers for writeback,
> analogous to the zbud allocator.
> 
> Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
> ---
>  mm/zsmalloc.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 2557b55ec767..776d0e15a401 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -225,6 +225,12 @@ struct link_free {
>  	};
>  };
> 
> +struct zs_pool;
> +
> +struct zs_ops {
> +	int (*evict)(struct zs_pool *pool, unsigned long handle);
> +};
> +
>  struct zs_pool {
>  	const char *name;
> 
> @@ -242,6 +248,9 @@ struct zs_pool {
>  #ifdef CONFIG_ZPOOL
>  	/* List tracking the zspages in LRU order by most recently added object */
>  	struct list_head lru;
> +	const struct zs_ops *ops;
> +	struct zpool *zpool;
> +	const struct zpool_ops *zpool_ops;
>  #endif
> 
>  #ifdef CONFIG_ZSMALLOC_STAT
> @@ -385,6 +394,18 @@ static void record_obj(unsigned long handle, unsigned long obj)
> 
>  #ifdef CONFIG_ZPOOL
> 
> +static int zs_zpool_evict(struct zs_pool *pool, unsigned long handle)
> +{
> +	if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
> +		return pool->zpool_ops->evict(pool->zpool, handle);
> +	else
> +		return -ENOENT;
> +}
> +
> +static const struct zs_ops zs_zpool_ops = {
> +	.evict =	zs_zpool_evict
> +};
> +
>  static void *zs_zpool_create(const char *name, gfp_t gfp,
>  			     const struct zpool_ops *zpool_ops,
>  			     struct zpool *zpool)
> @@ -394,7 +415,19 @@ static void *zs_zpool_create(const char *name, gfp_t gfp,
>  	 * different contexts and its caller must provide a valid
>  	 * gfp mask.
>  	 */
> -	return zs_create_pool(name);
> +	struct zs_pool *pool = zs_create_pool(name);
> +
> +	if (pool) {
> +		pool->zpool = zpool;
> +		pool->zpool_ops = zpool_ops;
> +
> +		if (zpool_ops)

I lost. When do we have zpool_ops as NULL?