Add the flags field to stack_print_ctx, and define two flags for current
behavior (printing stack traces and their number of base pages).

The plumbing of flags is debugfs_create_file(data) -> inode.i_private ->
page_owner_stack_open() -> stack_print_ctx.flags -> stack_print().

No behavior change intended.

Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
---
 mm/page_owner.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index c1a7d7afe945..e983ac21a4db 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -45,8 +45,12 @@ static struct stack failure_stack;
 static struct stack *stack_list;
 static DEFINE_SPINLOCK(stack_list_lock);
 
+#define STACK_PRINT_FLAG_STACK		0x1
+#define STACK_PRINT_FLAG_PAGES		0x2
+
 struct stack_print_ctx {
 	struct stack *stack;
+	u8 flags;
 };
 
 static bool page_owner_enabled __initdata;
@@ -901,20 +905,24 @@ static int stack_print(struct seq_file *m, void *v)
 	unsigned long *entries;
 	unsigned long nr_entries;
 	struct stack_record *stack_record = stack->stack_record;
+	struct stack_print_ctx *ctx = m->private;
 
 	if (!stack->stack_record)
 		return 0;
 
-	nr_entries = stack_record->size;
-	entries = stack_record->entries;
 	nr_base_pages = refcount_read(&stack_record->count) - 1;
 
 	if (nr_base_pages < 1 || nr_base_pages < page_owner_pages_threshold)
 		return 0;
 
-	for (i = 0; i < nr_entries; i++)
-		seq_printf(m, " %pS\n", (void *)entries[i]);
-	seq_printf(m, "nr_base_pages: %d\n\n", nr_base_pages);
+	if (ctx->flags & STACK_PRINT_FLAG_STACK) {
+		nr_entries = stack_record->size;
+		entries = stack_record->entries;
+		for (i = 0; i < nr_entries; i++)
+			seq_printf(m, " %pS\n", (void *)entries[i]);
+	}
+	if (ctx->flags & STACK_PRINT_FLAG_PAGES)
+		seq_printf(m, "nr_base_pages: %d\n\n", nr_base_pages);
 
 	return 0;
 }
@@ -935,6 +943,13 @@ static int page_owner_stack_open(struct inode *inode, struct file *file)
 	int ret = seq_open_private(file, &page_owner_stack_op,
 				   sizeof(struct stack_print_ctx));
 
+	if (!ret) {
+		struct seq_file *m = file->private_data;
+		struct stack_print_ctx *ctx = m->private;
+
+		ctx->flags = (uintptr_t) inode->i_private;
+	}
+
 	return ret;
 }
 
@@ -973,7 +988,9 @@ static int __init pageowner_init(void)
 	debugfs_create_file("page_owner", 0400, NULL, NULL,
 			    &proc_page_owner_operations);
 	dir = debugfs_create_dir("page_owner_stacks", NULL);
-	debugfs_create_file("show_stacks", 0400, dir, NULL,
+	debugfs_create_file("show_stacks", 0400, dir,
+			    (void *)(STACK_PRINT_FLAG_STACK |
+				     STACK_PRINT_FLAG_PAGES),
 			    &page_owner_stack_operations);
 	debugfs_create_file("count_threshold", 0600, dir, NULL,
 			    &proc_page_owner_threshold);
-- 
2.48.1