Re: [RFC PATCH 3/3] mm/zsmalloc: change ZS_MAX_PAGES_PER_ZSPAGE

[Sergey Senozhatsky]

On (02/18/16 13:41), Sergey Senozhatsky wrote:
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 0c9f117..d5252d1 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -73,12 +73,6 @@
>   */
>  #define ZS_ALIGN               8
>  
> -/*
> - * A single 'zspage' is composed of up ZS_MAX_PAGES_PER_ZSPAGE discontiguous
> - * 0-order (single) pages.
> - */
> -#define ZS_MAX_PAGES_PER_ZSPAGE        6
> -
>  #define ZS_HANDLE_SIZE (sizeof(unsigned long))
>  
>  /*
> @@ -149,6 +143,21 @@
>  #define ZS_SIZE_CLASS_DELTA    (PAGE_SIZE >> 8)
>  
>  /*
> + * We want to have at least this number of ->huge classes.
> + */
> +#define ZS_MIN_HUGE_CLASSES_NUM        32
> +/*
> + * A single 'zspage' is composed of up ZS_MAX_PAGES_PER_ZSPAGE discontiguous
> + * 0-order (single) pages.
> + *
> + * The smallest huge class will have CLASS_SIZE * SIZE_CLASS_DELTA of
> + * wasted space, calculate how many pages we need to fit a CLASS_SIZE
> + * object there and, thus, to save a additional zspage.
> + */
> +#define ZS_MAX_PAGES_PER_ZSPAGE        \
> +       (PAGE_SIZE / (ZS_MIN_HUGE_CLASSES_NUM * ZS_SIZE_CLASS_DELTA))
> +
> +/*
>   * We do not maintain any list for completely empty or full pages
>   */
>  enum fullness_group {

and the difference between ZS_MIN_HUGE_CLASSES_NUM 57 (BASE number of
->huge classes) and ZS_MIN_HUGE_CLASSES_NUM 32 is:

ZS_MIN_HUGE_CLASSES_NUM 57 (BASE)
1151078400 575501415 621494272        0 621494272       17        0        1
1151074304 575499905 621477888        0 621477888       17        0        1
1151074304 575516318 621363200        0 621363200       17        0        1
1151078400 575558182 621346816        0 621346816       17        0        1
1151078400 575599320 621531136        0 621531136       17        0        1

ZS_MIN_HUGE_CLASSES_NUM 32
1151074304 575483112 594194432        0 594194432       17        0        1
1151074304 575521895 593678336        0 593678336       17        0        1
1151074304 575570453 594173952        0 594173952       17        0        1
1151074304 575461842 594010112        0 594010112       17        0        1
1151074304 575537116 593879040        0 593879040       17        0        1


around 26MB of order-0 pages.

	-ss