linux-kernel - Re: [PATCH net-next 3/7] pool_pool: avoid calling compound

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Date:   Thu, 23 Sep 2021 11:33:54 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxarm@...neuler.org,
        hawk@...nel.org, jonathan.lemon@...il.com, alobakin@...me,
        willemb@...gle.com, cong.wang@...edance.com, pabeni@...hat.com,
        haokexin@...il.com, nogikh@...gle.com, elver@...gle.com,
        memxor@...il.com, edumazet@...gle.com, alexander.duyck@...il.com,
        dsahern@...il.com
Subject: Re: [PATCH net-next 3/7] pool_pool: avoid calling compound_head()
 for skb frag page

On Wed, Sep 22, 2021 at 05:41:27PM +0800, Yunsheng Lin wrote:
> As the pp page for a skb frag is always a head page, so make
> sure skb_pp_recycle() passes a head page to avoid calling
> compound_head() for skb frag page case.

Doesn't that rely on the driver mostly (i.e what's passed in skb_frag_set_page() ? 
None of the current netstack code assumes bv_page is the head page of a 
compound page.  Since our page_pool allocator can will allocate compound
pages for order > 0,  why should we rely on it ?

Thanks
/Ilias
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
> ---
>  include/linux/skbuff.h | 2 +-
>  net/core/page_pool.c   | 2 --
>  2 files changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 6bdb0db3e825..35eebc2310a5 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -4722,7 +4722,7 @@ static inline bool skb_pp_recycle(struct sk_buff *skb, void *data)
>  {
>  	if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
>  		return false;
> -	return page_pool_return_skb_page(virt_to_page(data));
> +	return page_pool_return_skb_page(virt_to_head_page(data));
>  }
>  
>  #endif	/* __KERNEL__ */
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index f7e71dcb6a2e..357fb53343a0 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -742,8 +742,6 @@ bool page_pool_return_skb_page(struct page *page)
>  {
>  	struct page_pool *pp;
>  
> -	page = compound_head(page);
> -
>  	/* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
>  	 * in order to preserve any existing bits, such as bit 0 for the
>  	 * head page of compound page and bit 1 for pfmemalloc page, so
> -- 
> 2.33.0
>