Re: [PATCH v10 6/7] mm,page_owner: Filter out stacks by a threshold

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Hi

On 2024/2/16 5:59, Oscar Salvador wrote:
We want to be able to filter out the stacks based on a threshold we can
can tune.
By writing to 'count_threshold' file, we can adjust the threshold value.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
---
  mm/page_owner.c | 23 ++++++++++++++++++++++-
  1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index e99fbf822dd6..e56c1e92eccf 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -846,6 +846,8 @@ static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
  	return stack;
  }
+static unsigned long page_owner_stack_threshold;
+
  static int stack_print(struct seq_file *m, void *v)
  {
  	int i, stack_count;
@@ -858,7 +860,8 @@ static int stack_print(struct seq_file *m, void *v)
  	entries = stack_record->entries;
  	stack_count = refcount_read(&stack_record->count) - 1;
- if (!nr_entries || nr_entries < 0 || stack_count < 1)
+	if (!nr_entries || nr_entries < 0 || stack_count < 1 ||
+	    stack_count < page_owner_stack_threshold)
  		return 0;
for (i = 0; i < nr_entries; i++)
@@ -891,6 +894,22 @@ static const struct file_operations page_owner_stack_operations = {
  	.release	= seq_release,
  };
+static int page_owner_threshold_get(void *data, u64 *val)
+{
+	*val = READ_ONCE(page_owner_stack_threshold);
+	return 0;
+}
+
+static int page_owner_threshold_set(void *data, u64 val)
+{
+	WRITE_ONCE(page_owner_stack_threshold, val);
+	return 0;
+}

no need READ/WRITE_ONCE between get/set, since simple_attr_read/write() with a mutex, but set and stack_print could date race
+
+DEFINE_SIMPLE_ATTRIBUTE(proc_page_owner_threshold, &page_owner_threshold_get,
+			&page_owner_threshold_set, "%llu");

%llu\n"

In addition, since we have a stack_list, could we add a new feature to
dump stack info with threshold with OOM notifier, because many users
directly call alloc_page family, which makes it too difficult to debug
during OOM.

Thanks

+
+
  static int __init pageowner_init(void)
  {
  	struct dentry *dir;
@@ -905,6 +924,8 @@ static int __init pageowner_init(void)
  	dir = debugfs_create_dir("page_owner_stacks", NULL);
  	debugfs_create_file("show_stacks", 0400, dir, NULL,
  			    &page_owner_stack_operations);
+	debugfs_create_file("count_threshold", 0600, dir, NULL,
+			    &proc_page_owner_threshold);
return 0;
  }




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