Subject: Re: [PATCH 30/38] cls_flower: Use XArray list of filters in fl_walk

From: Vlad Buslov <[email-masked]>
Date: Wed, 21 Aug 2019 18:32:07 +0000

On Wed 21 Aug 2019 at 01:32, Matthew Wilcox <[email-masked]> wrote:
> From: "Matthew Wilcox (Oracle)" <[email-masked]>
>
> Instead of iterating over every filter attached to every mark, just
> iterate over each filter.
>
> Signed-off-by: Matthew Wilcox (Oracle) <[email-masked]>
> ---
>  net/sched/cls_flower.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
> index 54026c9e9b05..2a1999d2b507 100644
> --- a/net/sched/cls_flower.c
> +++ b/net/sched/cls_flower.c
> @@ -575,18 +575,15 @@ static void fl_destroy(struct tcf_proto *tp, bool rtnl_held,
>  		       struct netlink_ext_ack *extack)
>  {
>  	struct cls_fl_head *head = fl_head_dereference(tp);
> -	struct fl_flow_mask *mask, *next_mask;
> -	struct cls_fl_filter *f, *next;
> +	struct cls_fl_filter *f;
> +	unsigned long handle;
>  	bool last;
>
> -	list_for_each_entry_safe(mask, next_mask, &head->masks, list) {
> -		list_for_each_entry_safe(f, next, &mask->filters, list) {
> -			__fl_delete(tp, f, &last, rtnl_held, extack);
> -			if (last)
> -				break;
> -		}
> +	xa_for_each(&head->filters, handle, f) {
> +		__fl_delete(tp, f, &last, rtnl_held, extack);
> +		if (last)
> +			break;
>  	}
> -	xa_destroy(&head->filters);
>
>  	__module_get(THIS_MODULE);
>  	tcf_queue_work(&head->rwork, fl_destroy_sleepable);

What is the motivation for this change? You substitute O(n) iteration
over linked list with O(nlogn) iteration over xarray without any
apparent benefit.