staging: zsmalloc: add ZS_MAX_PAGES_PER_ZSPAGE

This patch moves where max_zspage_order is declared and
changes its meaning.  "Order" typically implies 2^order
of something; however, it is currently being used as the
"maximum number of single pages in a zspage".  To add clarity,
ZS_MAX_ZSPAGE_ORDER is now used to calculate ZS_MAX_PAGES_PER_ZSPAGE,
which is 2^ZS_MAX_ZSPAGE_ORDER and is the upper bound on the number
of pages in a zspage.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zsmalloc/zsmalloc-main.c

@@ -186,7 +186,7 @@ static int get_zspage_order(int class_size)
 	/* zspage order which gives maximum used size per KB */
 	int max_usedpc_order = 1;
 
-	for (i = 1; i <= max_zspage_order; i++) {
+	for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
 		int zspage_size;
 		int waste, usedpc;
 

drivers/staging/zsmalloc/zsmalloc_int.h

@@ -25,6 +25,13 @@
  */
 #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.
+ */
+#define ZS_MAX_ZSPAGE_ORDER 2
+#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
+
 /*
  * Object location (<PFN>, <obj_idx>) is encoded as
  * as single (void *) handle value.
@@ -58,12 +65,6 @@
 #define ZS_SIZE_CLASSES		((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / \
 					ZS_SIZE_CLASS_DELTA + 1)
 
-/*
- * A single 'zspage' is composed of N discontiguous 0-order (single) pages.
- * This defines upper limit on N.
- */
-static const int max_zspage_order = 4;
-
 /*
  * We do not maintain any list for completely empty or full pages
  */