Commit 765973a0 authored by Oscar Salvador's avatar Oscar Salvador Committed by Andrew Morton
Browse files

mm,page_owner: display all stacks and their count 

This patch adds a new directory called 'page_owner_stacks' under
/sys/kernel/debug/, with a file called 'show_stacks' in it.  Reading from
that file will show all stacks that were added by page_owner followed by
their counting, giving us a clear overview of stack <-> count
relationship.

E.g:

  prep_new_page+0xa9/0x120
  get_page_from_freelist+0x801/0x2210
  __alloc_pages+0x18b/0x350
  alloc_pages_mpol+0x91/0x1f0
  folio_alloc+0x14/0x50
  filemap_alloc_folio+0xb2/0x100
  __filemap_get_folio+0x14a/0x490
  ext4_write_begin+0xbd/0x4b0 [ext4]
  generic_perform_write+0xc1/0x1e0
  ext4_buffered_write_iter+0x68/0xe0 [ext4]
  ext4_file_write_iter+0x70/0x740 [ext4]
  vfs_write+0x33d/0x420
  ksys_write+0xa5/0xe0
  do_syscall_64+0x80/0x160
  entry_SYSCALL_64_after_hwframe+0x6e/0x76
 stack_count: 4578

The seq stack_{start,next} functions will iterate through the list
stack_list in order to print all stacks.

Link: https://lkml.kernel.org/r/20240215215907.20121-6-osalvador@suse.de


Signed-off-by: default avatarOscar Salvador <osalvador@suse.de>
Acked-by: default avatarMarco Elver <elver@google.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarAndrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 217b2119

mm/page_owner.c

+92 −1
Original line number Diff line number Diff line
@@ -171,7 +171,13 @@ static void add_stack_record_to_list(struct stack_record *stack_record, 


	spin_lock_irqsave(&stack_list_lock, flags);

	stack->next = stack_list;

	stack_list = stack;

	/*

	 * This pairs with smp_load_acquire() from function

	 * stack_start(). This guarantees that stack_start()

	 * will see an updated stack_list before starting to

	 * traverse the list.

	 */

	smp_store_release(&stack_list, stack);

	spin_unlock_irqrestore(&stack_list_lock, flags);

}
@@ -805,8 +811,90 @@ static const struct file_operations proc_page_owner_operations = { 
	.llseek		= lseek_page_owner,

};



static void *stack_start(struct seq_file *m, loff_t *ppos)

{

	struct stack *stack;



	if (*ppos == -1UL)

		return NULL;



	if (!*ppos) {

		/*

		 * This pairs with smp_store_release() from function

		 * add_stack_record_to_list(), so we get a consistent

		 * value of stack_list.

		 */

		stack = smp_load_acquire(&stack_list);

	} else {

		stack = m->private;

		stack = stack->next;

	}



	m->private = stack;



	return stack;

}



static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)

{

	struct stack *stack = v;



	stack = stack->next;

	*ppos = stack ? *ppos + 1 : -1UL;

	m->private = stack;



	return stack;

}



static int stack_print(struct seq_file *m, void *v)

{

	int i, stack_count;

	struct stack *stack = v;

	unsigned long *entries;

	unsigned long nr_entries;

	struct stack_record *stack_record = stack->stack_record;



	nr_entries = stack_record->size;

	entries = stack_record->entries;

	stack_count = refcount_read(&stack_record->count) - 1;



	if (!nr_entries || nr_entries < 0 || stack_count < 1)

		return 0;



	for (i = 0; i < nr_entries; i++)

		seq_printf(m, " %pS\n", (void *)entries[i]);

	seq_printf(m, "stack_count: %d\n\n", stack_count);



	return 0;

}



static void stack_stop(struct seq_file *m, void *v)

{

}



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, 0);

}



static 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)

{

	struct dentry *dir;



	if (!static_branch_unlikely(&page_owner_inited)) {

		pr_info("page_owner is disabled\n");

		return 0;
@@ -814,6 +902,9 @@ 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,

			    &page_owner_stack_operations);



	return 0;

}