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.
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Acked-by: Marco Elver <elver@xxxxxxxxxx>
---
mm/page_owner.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 92 insertions(+), 1 deletion(-)
diff --git a/mm/page_owner.c b/mm/page_owner.c
index df6a923af5de..5258a417f4d1 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -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;
+ 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;
+
+ if (!nr_entries || nr_entries < 0 ||
+ refcount_read(&stack_record->count) < 2)
+ 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", refcount_read(&stack_record->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;
}
--
2.43.0
