[PATCH v4 2/3] mm, page_owner: Add page_owner_stacks file to print out only stacks and their counte

[Oscar Salvador <osalvador@xxxxxxx>]

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, so we can have a more global view.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx
---
 include/linux/stackdepot.h |  6 ++++
 lib/stackdepot.c           | 73 ++++++++++++++++++++++++++++++++++++++
 mm/page_owner.c            | 28 +++++++++++++++
 3 files changed, 107 insertions(+)

diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index b94d33312839..e1d05d9adcd1 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -116,6 +116,12 @@ depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
 					     gfp_t gfp_flags,
 					     bool counter);
 
+#ifdef CONFIG_PAGE_OWNER
+void *stack_start(struct seq_file *m, loff_t *ppos);
+void *stack_next(struct seq_file *m, void *v, loff_t *ppos);
+int stack_print(struct seq_file *m, void *v);
+#endif
+
 /**
  * stack_depot_fetch - Fetch a stack trace from stack depot
  *
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index e99f4ef218ef..d0a4e6ac0bc9 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -28,6 +28,8 @@
 #include <linux/types.h>
 #include <linux/memblock.h>
 #include <linux/kasan-enabled.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
 
 #define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
 
@@ -499,6 +501,77 @@ static struct stack_record *stack_depot_getstack(depot_stack_handle_t handle)
 	return stack;
 }
 
+#ifdef CONFIG_PAGE_OWNER
+void *stack_start(struct seq_file *m, loff_t *ppos)
+{
+	unsigned long *table = m->private;
+	struct stack_record **stacks, *stack;
+
+	/* First time */
+	if (*ppos == 0)
+		*table = 0;
+
+	if (*ppos == -1UL)
+		return NULL;
+
+	stacks = &stack_table[*table];
+	stack = (struct stack_record *)stacks;
+
+	return stack;
+}
+
+void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
+{
+	unsigned long *table = m->private;
+	unsigned long nr_table = *table;
+	struct stack_record *next = NULL, *stack = v, **stacks;
+	unsigned long stack_table_entries = stack_hash_mask + 1;
+
+	if (!stack) {
+new_table:
+		/* New table */
+		nr_table++;
+		if (nr_table >= stack_table_entries)
+			goto out;
+		stacks = &stack_table[nr_table];
+		stack = (struct stack_record *)stacks;
+		next = stack;
+	} else {
+		next = stack->next;
+	}
+
+	if (!next)
+		goto new_table;
+
+out:
+	*table = nr_table;
+	*ppos = (nr_table >= stack_table_entries) ? -1UL : *ppos + 1;
+	return next;
+}
+
+int stack_print(struct seq_file *m, void *v)
+{
+	char *buf;
+	int ret = 0;
+	struct stack_record *stack =v;
+
+	if (!stack->size || stack->size < 0 ||
+	    stack->size > PAGE_SIZE || stack->handle.valid != 1 ||
+	    refcount_read(&stack->count) < 1)
+		return 0;
+
+	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	ret += stack_trace_snprint(buf, PAGE_SIZE, stack->entries, stack->size, 0);
+	scnprintf(buf + ret, PAGE_SIZE - ret, "stack count: %d\n\n",
+		  refcount_read(&stack->count));
+	seq_printf(m, buf);
+	seq_puts(m, "\n\n");
+	kfree(buf);
+
+        return 0;
+}
+#endif
+
 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries)
 {
diff --git a/mm/page_owner.c b/mm/page_owner.c
index b6637524e442..b191ad1d41f9 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -718,6 +718,31 @@ static const struct file_operations proc_page_owner_operations = {
 	.llseek		= lseek_page_owner,
 };
 
+static void stack_stop(struct seq_file *m, void *v)
+{
+	return;
+}
+
+static const struct seq_operations page_owner_stack_op = {
+	.start  = stack_start,
+	.next   = stack_next,
+	.stop   = stack_stop,
+	.show   = stack_print
+};
+
+static int page_owner_stack_open(struct inode *inode, struct file *file)
+{
+	return seq_open_private(file, &page_owner_stack_op,
+				sizeof(unsigned long));
+}
+
+const struct file_operations page_owner_stack_operations = {
+	.open           = page_owner_stack_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = seq_release,
+};
+
 static int __init pageowner_init(void)
 {
 	if (!static_branch_unlikely(&page_owner_inited)) {
@@ -728,6 +753,9 @@ static int __init pageowner_init(void)
 	debugfs_create_file("page_owner", 0400, NULL, NULL,
 			    &proc_page_owner_operations);
 
+	debugfs_create_file("page_owner_stacks", S_IRUSR, NULL, NULL,
+			     &page_owner_stack_operations);
+
 	return 0;
 }
 late_initcall(pageowner_init)
-- 
2.35.3