linux-kernel - Re: [PATCH bpf-next v3 4/4] xdp: remove unused {__,}xdp_release

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Date:   Tue, 14 Mar 2023 19:37:23 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>
CC:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Song Liu <song@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Menglong Dong <imagedong@...cent.com>,
        Mykola Lysenko <mykolal@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 4/4] xdp: remove unused
 {__,}xdp_release_frame()

On 2023/3/14 5:55, Alexander Lobakin wrote:
> __xdp_build_skb_from_frame() was the last user of
> {__,}xdp_release_frame(), which detaches pages from the page_pool.
> All the consumers now recycle Page Pool skbs and page, except mlx5,
> stmmac and tsnep drivers, which use page_pool_release_page() directly
> (might change one day). It's safe to assume this functionality is not
> needed anymore and can be removed (in favor of recycling).
> 
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> ---
>  include/net/xdp.h | 29 -----------------------------
>  net/core/xdp.c    | 15 ---------------
>  2 files changed, 44 deletions(-)
> 
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index d517bfac937b..5393b3ebe56e 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -317,35 +317,6 @@ void xdp_flush_frame_bulk(struct xdp_frame_bulk *bq);
>  void xdp_return_frame_bulk(struct xdp_frame *xdpf,
>  			   struct xdp_frame_bulk *bq);
>  
> -/* When sending xdp_frame into the network stack, then there is no
> - * return point callback, which is needed to release e.g. DMA-mapping
> - * resources with page_pool.  Thus, have explicit function to release
> - * frame resources.
> - */
> -void __xdp_release_frame(void *data, struct xdp_mem_info *mem);
> -static inline void xdp_release_frame(struct xdp_frame *xdpf)
> -{
> -	struct xdp_mem_info *mem = &xdpf->mem;
> -	struct skb_shared_info *sinfo;
> -	int i;
> -
> -	/* Curr only page_pool needs this */
> -	if (mem->type != MEM_TYPE_PAGE_POOL)
> -		return;
> -
> -	if (likely(!xdp_frame_has_frags(xdpf)))
> -		goto out;
> -
> -	sinfo = xdp_get_shared_info_from_frame(xdpf);
> -	for (i = 0; i < sinfo->nr_frags; i++) {
> -		struct page *page = skb_frag_page(&sinfo->frags[i]);
> -
> -		__xdp_release_frame(page_address(page), mem);
> -	}
> -out:
> -	__xdp_release_frame(xdpf->data, mem);
> -}
> -
>  static __always_inline unsigned int xdp_get_frame_len(struct xdp_frame *xdpf)
>  {
>  	struct skb_shared_info *sinfo;
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index a2237cfca8e9..8d3ad315f18d 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -531,21 +531,6 @@ void xdp_return_buff(struct xdp_buff *xdp)
>  }
>  EXPORT_SYMBOL_GPL(xdp_return_buff);
>  
> -/* Only called for MEM_TYPE_PAGE_POOL see xdp.h */
> -void __xdp_release_frame(void *data, struct xdp_mem_info *mem)
> -{
> -	struct xdp_mem_allocator *xa;
> -	struct page *page;
> -
> -	rcu_read_lock();
> -	xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> -	page = virt_to_head_page(data);
> -	if (xa)
> -		page_pool_release_page(xa->page_pool, page);

page_pool_release_page() is only call here when xa is not NULL
and mem->type == MEM_TYPE_PAGE_POOL.

But skb_mark_for_recycle() is call when mem->type == MEM_TYPE_PAGE_POOL
without checking xa, it does not seems symmetric to patch 3, if this is
intended?

> -	rcu_read_unlock();
> -}
> -EXPORT_SYMBOL_GPL(__xdp_release_frame);
> -
>  void xdp_attachment_setup(struct xdp_attachment_info *info,
>  			  struct netdev_bpf *bpf)
>  {
>