On (02/18/16 12:02), Sergey Senozhatsky wrote:
[..]
> ---
> mm/zsmalloc.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 61b1b35..0c9f117 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -74,11 +74,10 @@
> #define ZS_ALIGN 8
>
> /*
> - * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single)
> - * pages. ZS_MAX_ZSPAGE_ORDER defines upper limit on N.
> + * A single 'zspage' is composed of up ZS_MAX_PAGES_PER_ZSPAGE discontiguous
> + * 0-order (single) pages.
> */
> -#define ZS_MAX_ZSPAGE_ORDER 2
> -#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
> +#define ZS_MAX_PAGES_PER_ZSPAGE 6
>
> #define ZS_HANDLE_SIZE (sizeof(unsigned long))
>
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)
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.
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 {
--
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