On (02/18/16 13:41), Sergey Senozhatsky wrote:
> I think we better switch to different logic here -- specify how many ->huge
> classes we want to have, and let zsmalloc to calculate
> ZS_MAX_PAGES_PER_ZSPAGE.
>
>
> For example, if we want to have 20 ->huge classes, the 'smallest' (or the
> last)
^^^ largest
> non-huge class will have CLASS_SIZE * SIZE_CLASS_DELTA of spare (wasted)
> space,
> so PAGE_SIZE / (CLASS_SIZE * SIZE_CLASS_DELTA) will give us the number of
> pages
> we need to form into a zspage to make it the last huge class.
^^ 'non-huge'... what is the
correct english word I'm
looking
for...
-ss
> setting ZS_MIN_HUGE_CLASSES_NUM to 32 gives us (on x86_64, PAGE_SHIFT 12)
> ->huge
> class size range of [3648, 4096]. so all objects smaller than 3648 will not
> waste
> an entire zspage (and order-0 page), but will share the page with another
> objects
> of that size.
>
>
> something like this:
>
> ---
>
> 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 {
>
