Re: [PATCHv4 6/9] zsmalloc: pass limit on pages per-zspage to zs_create_pool()

[Minchan Kim]

On Mon, Oct 31, 2022 at 02:41:05PM +0900, Sergey Senozhatsky wrote:
> Allow zsmalloc pool owner to specify max number of pages
> per-zspage (during pool creation), so that different pools
> can have different characteristics.
> 
> By default we pass ZS_DEFAULT_PAGES_PER_ZSPAGE which is 4
> (matches the current order 2 zspages limit).

How could user decide what's the best size for their workload?

> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> ---
>  drivers/block/zram/zram_drv.c |  3 ++-
>  include/linux/zsmalloc.h      |  2 +-
>  mm/zsmalloc.c                 | 11 +++++++----
>  3 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 90b0c66bbd5b..bec02f636bce 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1247,7 +1247,8 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
>  	if (!zram->table)
>  		return false;
>  
> -	zram->mem_pool = zs_create_pool(zram->disk->disk_name);
> +	zram->mem_pool = zs_create_pool(zram->disk->disk_name,
> +					ZS_DEFAULT_PAGES_PER_ZSPAGE);
>  	if (!zram->mem_pool) {
>  		vfree(zram->table);
>  		return false;
> diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
> index b6b8654a2d45..28f2b9cb1c47 100644
> --- a/include/linux/zsmalloc.h
> +++ b/include/linux/zsmalloc.h
> @@ -50,7 +50,7 @@ struct zs_pool_stats {
>  
>  struct zs_pool;
>  
> -struct zs_pool *zs_create_pool(const char *name);
> +struct zs_pool *zs_create_pool(const char *name, unsigned long num_pages);
>  void zs_destroy_pool(struct zs_pool *pool);
>  
>  unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t flags);
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index d329bd673baa..42987a913f45 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -366,7 +366,7 @@ 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);
> +	return zs_create_pool(name, ZS_DEFAULT_PAGES_PER_ZSPAGE);
>  }
>  
>  static void zs_zpool_destroy(void *pool)
> @@ -2195,6 +2195,7 @@ static int zs_register_shrinker(struct zs_pool *pool)
>  /**
>   * zs_create_pool - Creates an allocation pool to work from.
>   * @name: pool name to be created
> + * @num_pages: maximum number of pages per-zspage

How about "max_page_chain:"? 

>   *
>   * This function must be called before anything when using
>   * the zsmalloc allocator.
> @@ -2202,18 +2203,20 @@ static int zs_register_shrinker(struct zs_pool *pool)
>   * On success, a pointer to the newly created pool is returned,
>   * otherwise NULL.
>   */
> -struct zs_pool *zs_create_pool(const char *name)
> +struct zs_pool *zs_create_pool(const char *name, unsigned long num_pages)
>  {
>  	int i;
>  	struct zs_pool *pool;
>  	struct size_class *prev_class = NULL;
> -	unsigned long num_pages;
> +
> +	if (WARN_ON(num_pages < ZS_MIN_PAGES_PER_ZSPAGE ||
> +		    num_pages > ZS_MAX_PAGES_PER_ZSPAGE))
> +		return NULL;
>  
>  	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
>  	if (!pool)
>  		return NULL;
>  
> -	num_pages = ZS_DEFAULT_PAGES_PER_ZSPAGE;
>  	/* min_alloc_size must be multiple of ZS_ALIGN */
>  	pool->min_alloc_size = num_pages << PAGE_SHIFT >> OBJ_INDEX_BITS;
>  	pool->min_alloc_size = max(pool->min_alloc_size, ZS_MIN_ALLOC_SIZE);
> -- 
> 2.38.1.273.g43a17bfeac-goog
>