[PATCH v2] lib: stackdepot: Add support to configure STACK_HASH_SIZE

[vjitta@codeaurora.org]

From: Yogesh Lal <ylal@codeaurora.org>

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@kernel.org>
Signed-off-by: Yogesh Lal <ylal@codeaurora.org>
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
---
 lib/stackdepot.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 81c69c0..ce53598 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -141,14 +141,31 @@ 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)
+static unsigned int stack_hash_order = 20;
+#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 struct stack_record **stack_table;
+
+static int __init setup_stack_hash_order(char *str)
+{
+	kstrtouint(str, 0, &stack_hash_order);
+	return 0;
+}
+early_param("stack_hash_order", setup_stack_hash_order);
+
+static int __init init_stackdepot(void)
+{
+	int i;
+
+	stack_table = kvmalloc(sizeof(struct stack_record *) * STACK_HASH_SIZE, GFP_KERNEL);
+	for (i = 0; i < STACK_HASH_SIZE; i++)
+		stack_table[i] = NULL;
+	return 0;
+}
+
+early_initcall(init_stackdepot);
 
 /* Calculate hash for a stack */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
-- 
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