[PATCH v3] lib: stackdepot: Add support to configure STACK_HASH_SIZE

[vjitta]

From: Yogesh Lal <ylal@xxxxxxxxxxxxxx>

Add a kernel parameter stack_hash_order to configure STACK_HASH_SIZE.

Aim is to have configurable value for STACK_HASH_SIZE, so that one
can configure it depending on usecase there by reducing the static
memory overhead.

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.

Suggested-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Yogesh Lal <ylal@xxxxxxxxxxxxxx>
Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
---
 lib/stackdepot.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 81c69c0..e0eebfd 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -30,6 +30,7 @@
 #include <linux/stackdepot.h>
 #include <linux/string.h>
 #include <linux/types.h>
+#include <linux/vmalloc.h>
 
 #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
 
@@ -141,14 +142,36 @@ 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 MAX_STACK_HASH_ORDER 20
+#define MAX_STACK_HASH_SIZE (1L << MAX_STACK_HASH_ORDER)
+#define STACK_HASH_SIZE (1L << stack_hash_order)
 #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
 #define STACK_HASH_SEED 0x9747b28c
 
-static struct stack_record *stack_table[STACK_HASH_SIZE] = {
-	[0 ...	STACK_HASH_SIZE - 1] = NULL
+static unsigned int stack_hash_order = 20;
+static struct stack_record *stack_table_def[MAX_STACK_HASH_SIZE] __initdata = {
+	[0 ...  MAX_STACK_HASH_SIZE - 1] = NULL
 };
+static struct stack_record **stack_table __refdata = stack_table_def;
+
+static int __init setup_stack_hash_order(char *str)
+{
+	kstrtouint(str, 0, &stack_hash_order);
+	if (stack_hash_order > MAX_STACK_HASH_ORDER)
+		stack_hash_order = MAX_STACK_HASH_ORDER;
+	return 0;
+}
+early_param("stack_hash_order", setup_stack_hash_order);
+
+static int __init init_stackdepot(void)
+{
+	size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
+
+	stack_table = vmalloc(size);
+	memcpy(stack_table, stack_table_def, size);
+	return 0;
+}
+early_initcall(init_stackdepot);
 
 /* Calculate hash for a stack */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
-- 
2.7.4
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