iommu/iova: change IOVA_MAG_SIZE to 127 to save memory

kmalloc will round up the request size to power of 2, and current
iova_magazine's size is 1032 (1024+8) bytes, so each instance
allocated will get 2048 bytes from kmalloc, causing around 1KB
waste.

Change IOVA_MAG_SIZE from 128 to 127 to make size of 'iova_magazine'
1024 bytes so that no memory will be wasted.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20220703114450.15184-1-feng.tang@intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: ftang1

drivers/iommu/iova.c

@@ -614,7 +614,12 @@ EXPORT_SYMBOL_GPL(reserve_iova);
  * dynamic size tuning described in the paper.
  */
 
-#define IOVA_MAG_SIZE 128
+/*
+ * As kmalloc's buffer size is fixed to power of 2, 127 is chosen to
+ * assure size of 'iova_magazine' to be 1024 bytes, so that no memory
+ * will be wasted.
+ */
+#define IOVA_MAG_SIZE 127
 #define MAX_GLOBAL_MAGS 32	/* magazines per bin */
 
 struct iova_magazine {