[PATCH 1/3] mm/page_owner: add option 'print_handle' for 'show_stacks'

[Mauricio Faria de Oliveira <mfo@igalia.com>]

For monitoring the memory usage per stack trace, it is more efficient to
use the handle number as unique identifier of a stack trace than to, for
example, read/hash all stack traces to uniquely identify them everytime.

The handle number is a unique identifier for stack traces in stackdepot.

This patch adds the option 'print_handle' to print the handle number of
stack traces in 'show_stacks'.

Testing:

  - Without handles (default):
  # cat /sys/kernel/debug/page_owner_stacks/show_stacks > f1

  - With handles (new option):
  # echo 1 >/sys/kernel/debug/page_owner_stacks/print_handle
  # cat /sys/kernel/debug/page_owner_stacks/show_stacks > f2

  - Same number of lines for 'nr_base_pages' and 'handle':
  # grep -c '^nr_base_pages:' f1
  873
  # grep -c '^handle:' f2
  873

Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
---
 mm/page_owner.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index c3ca21132c2c..420426749239 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -887,6 +887,7 @@ static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
 }
 
 static unsigned long page_owner_pages_threshold;
+static bool page_owner_print_handle;
 
 static int stack_print(struct seq_file *m, void *v)
 {
@@ -908,6 +909,8 @@ static int stack_print(struct seq_file *m, void *v)
 
 	for (i = 0; i < nr_entries; i++)
 		seq_printf(m, " %pS\n", (void *)entries[i]);
+	if (page_owner_print_handle)
+		seq_printf(m, "handle: %d\n", stack_record->handle.handle);
 	seq_printf(m, "nr_base_pages: %d\n\n", nr_base_pages);
 
 	return 0;
@@ -968,6 +971,8 @@ static int __init pageowner_init(void)
 			    &page_owner_stack_operations);
 	debugfs_create_file("count_threshold", 0600, dir, NULL,
 			    &proc_page_owner_threshold);
+	debugfs_create_bool("print_handle", 0600, dir,
+			    &page_owner_print_handle);
 
 	return 0;
 }
-- 
2.48.1