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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

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@suse.de>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>   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;
>   }