[RFC 1/6] zsmalloc: expand size class to support sizeof(unsigned long)

[Minchan Kim <minchan@kernel.org>]

For compaction of zsmalloc, we need to decouple handle and
obj position binding. For that, we need another memory to
keep handle and I want to reuse existing functions of zsmalloc
to implement indirect layer.

For that, we need to support new size class(ie, sizeof(unsigned
long)) so this patch does it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 2021df5eb891..a806d714924c 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -100,7 +100,8 @@
  * span more than 1 page which avoids complex case of mapping 2 pages simply
  * to restore link_free pointer values.
  */
-#define ZS_ALIGN		8
+#define ZS_ALIGN		(sizeof(struct link_free))
+#define ZS_HANDLE_SIZE		(sizeof(unsigned long))
 
 /*
  * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single)
@@ -138,11 +139,11 @@
 #define MAX(a, b) ((a) >= (b) ? (a) : (b))
 /* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
 #define ZS_MIN_ALLOC_SIZE \
-	MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
-#define ZS_MAX_ALLOC_SIZE	PAGE_SIZE
+	MAX(ZS_ALIGN, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
+#define ZS_MAX_ALLOC_SIZE	(PAGE_SIZE + ZS_HANDLE_SIZE)
 
 /*
- * On systems with 4K page size, this gives 255 size classes! There is a
+ * On systems with 4K page size, this gives 257 size classes! There is a
  * trader-off here:
  *  - Large number of size classes is potentially wasteful as free page are
  *    spread across these classes
-- 
2.0.0

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