[PATCH 2/3] mm, page_owner: Add page_owner_stacks file to print out only stacks and their counter

[Oscar Salvador <osalvador@suse.de>]

We might be only interested in knowing about stacks <-> count
relationship, so instead of having to fiddle with page_owner
output and screen through pfns, let us add a new file called
'page_owner_stacks' that does just that.
By cating such file, we will get all the stacktraces followed by
its counter (allocated - freed times), so we can have a more specific
overview.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 include/linux/stackdepot.h |  2 ++
 lib/stackdepot.c           | 40 ++++++++++++++++++++++++++++++++++++++
 mm/page_owner.c            | 30 ++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)

diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index 5ee0cf5be88f..20f62039f23a 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -25,6 +25,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 					gfp_t gfp_flags, bool can_alloc,
 					stack_action_t action);
 void stack_depot_dec_count(depot_stack_handle_t handle);
+int stack_depot_print_stacks_threshold(char *buf, size_t size, loff_t *pos,
+				       unsigned long *last_stack);
 
 /*
  * Every user of stack depot has to call stack_depot_init() during its own init
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index aeb59d3557e2..3090ae0f3958 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -526,3 +526,43 @@ depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
 	return __stack_depot_save(entries, nr_entries, alloc_flags, true, action);
 }
 EXPORT_SYMBOL_GPL(stack_depot_save_action);
+
+int stack_depot_print_stacks_threshold(char *buf, size_t size, loff_t *pos,
+				       unsigned long *last_stack)
+{
+	struct stack_record *stack = NULL, *last;
+	struct stack_record **stacks;
+	int i = *pos, ret = 0;
+
+	/* Continue from the last week if we have one */
+	if (*last_stack) {
+		last = (struct stack_record *)*last_stack;
+		stack = last->next;
+	} else {
+new_table:
+		stacks = &stack_table[i];
+		stack = (struct stack_record *)stacks;
+	}
+
+	for (; stack; stack = stack->next) {
+		if (!stack->size || stack->size < 0 ||
+		    stack->size > size || stack->handle.valid != 1 ||
+		    refcount_read(&stack->count) < 1)
+			continue;
+
+		ret += stack_trace_snprint(buf, size, stack->entries, stack->size, 0);
+		ret += scnprintf(buf + ret, size - ret, "stack count: %d\n\n",
+				 refcount_read(&stack->count));
+		*last_stack = (unsigned long)stack;
+		return ret;
+	}
+
+	i++;
+	*pos = i;
+
+	/* Keep looking all tables for valid stacks */
+	if (i < STACK_HASH_SIZE)
+		goto new_table;
+
+	return 0;
+}
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 794f346d7520..8c67c7eb2451 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -43,6 +43,8 @@ static depot_stack_handle_t early_handle;
 
 static void init_early_allocated_pages(void);
 
+static unsigned long last_stack = 0;
+
 static int __init early_page_owner_param(char *buf)
 {
 	int ret = kstrtobool(buf, &page_owner_enabled);
@@ -663,6 +665,32 @@ static void init_early_allocated_pages(void)
 		init_zones_in_node(pgdat);
 }
 
+static ssize_t read_page_owner_stacks(struct file *file, char __user *buf,
+				      size_t count, loff_t *pos)
+{
+	char *kbuf;
+	int ret = 0;
+
+	count = min_t(size_t, count, PAGE_SIZE);
+	kbuf = kmalloc(count, GFP_KERNEL);
+	if (!kbuf)
+		return ENOMEM;
+
+	ret += stack_depot_print_stacks_threshold(kbuf, count, pos, &last_stack);
+	if (copy_to_user(buf, kbuf, ret))
+		ret = -EFAULT;
+
+	if (!ret)
+		last_stack = 0;
+
+	kfree(kbuf);
+	return ret;
+}
+
+static const struct file_operations proc_page_owner_stacks = {
+	.read = read_page_owner_stacks,
+};
+
 static const struct file_operations proc_page_owner_operations = {
 	.read		= read_page_owner,
 };
@@ -676,6 +704,8 @@ static int __init pageowner_init(void)
 
 	debugfs_create_file("page_owner", 0400, NULL, NULL,
 			    &proc_page_owner_operations);
+	debugfs_create_file("page_owner_stacks", 0400, NULL, NULL,
+			    &proc_page_owner_stacks);
 
 	return 0;
 }
-- 
2.35.3