linux-kernel - Re: [PATCHv2 2/6] zsmalloc: remove stat and fullness enums

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Date:   Thu, 23 Feb 2023 15:11:27 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 2/6] zsmalloc: remove stat and fullness enums

On Thu, Feb 23, 2023 at 12:04:47PM +0900, Sergey Senozhatsky wrote:
> The fullness_group enum is nested (sub-enum) within the
> class_stat_type enum. zsmalloc requires the values in both
> enums to match, because zsmalloc passes these values to
> generic functions, e.g. class_stat_inc() and class_stat_dec(),
> after casting them to integers.
> 
> Replace these enums (and enum nesting) and use simple defines
> instead. Also rename some of zsmalloc stats defines, as they
> sort of clash with zspage object tags.
> 
> Suggested-by: Yosry Ahmed <yosryahmed@...gle.com>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  mm/zsmalloc.c | 104 ++++++++++++++++++++++----------------------------
>  1 file changed, 45 insertions(+), 59 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index b57a89ed6f30..38ae8963c0eb 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -159,26 +159,18 @@
>  #define ZS_SIZE_CLASSES	(DIV_ROUND_UP(ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE, \
>  				      ZS_SIZE_CLASS_DELTA) + 1)
>  
> -enum fullness_group {
> -	ZS_EMPTY,
> -	ZS_ALMOST_EMPTY,
> -	ZS_ALMOST_FULL,
> -	ZS_FULL,
> -	NR_ZS_FULLNESS,
> -};
> +#define ZS_EMPTY		0
> +#define ZS_ALMOST_EMPTY		1
> +#define ZS_ALMOST_FULL		2
> +#define ZS_FULL			3
> +#define ZS_OBJS_ALLOCATED	4
> +#define ZS_OBJS_INUSE		5
>  
> -enum class_stat_type {
> -	CLASS_EMPTY,
> -	CLASS_ALMOST_EMPTY,
> -	CLASS_ALMOST_FULL,
> -	CLASS_FULL,
> -	OBJ_ALLOCATED,
> -	OBJ_USED,
> -	NR_ZS_STAT_TYPE,
> -};
> +#define NR_ZS_STAT		6
> +#define NR_ZS_FULLNESS		4

Using define list instead of enum list looks like going backward. :)

Why can't we do this?

enum class_stat_type {
    ZS_EMPTY,
    ZS_ALMOST_EMPTY,
    ZS_ALMOST_FULL,
    ZS_FULL,
    NR_ZS_FULLNESS,
    ZS_OBJ_ALLOCATED = NR_ZS_FULLNESS,
    ZS_OBJ_USED,
    NR_ZS_STAT,
}


};
>  
>  struct zs_size_stat {
> -	unsigned long objs[NR_ZS_STAT_TYPE];
> +	unsigned long objs[NR_ZS_STAT];
>  };
>