lib: stackdepot: Add support to configure STACK_HASH_SIZE

Use STACK_HASH_ORDER_SHIFT to configure STACK_HASH_SIZE.

Aim is to have configurable value for  STACK_HASH_SIZE,
so depend on use case one can configure it.

One example is of Page Owner, default value of
STACK_HASH_SIZE lead stack depot to consume 8MB of static memory.
Making it configurable and use lower value helps to enable features like
CONFIG_PAGE_OWNER without any significant overhead.

Change-Id: If6b64d4d4d42c763b00e2719fde5a25e94c10597
Signed-off-by: Yogesh Lal <ylal@codeaurora.org>

lib/Kconfig

@@ -574,6 +574,15 @@ config STACKDEPOT
 	bool
 	select STACKTRACE
 
+config STACK_HASH_ORDER_SHIFT
+	int "stack depot hash size (12 => 4KB, 20 => 1024KB)"
+	range 12 20
+	default 20
+	depends on STACKDEPOT
+	help
+	 Select the hash size as a power of 2 for the stackdepot hash table.
+	 Choose a lower value to reduce the memory impact.
+
 config SBITMAP
 	bool
 

lib/stackdepot.c

@@ -146,8 +146,7 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
 	return stack;
 }
 
-#define STACK_HASH_ORDER 20
-#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
+#define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER_SHIFT)
 #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
 #define STACK_HASH_SEED 0x9747b28c