Re: [PATCH v5 net-next 09/11] skbuff: allow to optionally use NAPI cache from __alloc_skb()

[Alexander Duyck]

On Thu, Feb 11, 2021 at 11:00 AM Alexander Lobakin <alobakin@xxxxx> wrote:
>
> Reuse the old and forgotten SKB_ALLOC_NAPI to add an option to get
> an skbuff_head from the NAPI cache instead of inplace allocation
> inside __alloc_skb().
> This implies that the function is called from softirq or BH-off
> context, not for allocating a clone or from a distant node.
>
> Signed-off-by: Alexander Lobakin <alobakin@xxxxx>
> ---
>  net/core/skbuff.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 9e1a8ded4acc..a0b457ae87c2 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -397,15 +397,20 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
>         struct sk_buff *skb;
>         u8 *data;
>         bool pfmemalloc;
> +       bool clone;
>
> -       cache = (flags & SKB_ALLOC_FCLONE)
> -               ? skbuff_fclone_cache : skbuff_head_cache;
> +       clone = !!(flags & SKB_ALLOC_FCLONE);

The boolean conversion here is probably unnecessary. I would make
clone an int like flags and work with that. I suspect the compiler is
doing it already, but it is better to be explicit.

> +       cache = clone ? skbuff_fclone_cache : skbuff_head_cache;
>
>         if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
>                 gfp_mask |= __GFP_MEMALLOC;
>
>         /* Get the HEAD */
> -       skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);
> +       if ((flags & SKB_ALLOC_NAPI) && !clone &&

Rather than having to do two checks you could just check for
SKB_ALLOC_NAPI and SKB_ALLOC_FCLONE in a single check. You could just
do something like:
    if ((flags & (SKB_ALLOC_FCLONE | SKB_ALLOC_NAPI) == SKB_ALLOC_NAPI)

That way you can avoid the extra conditional jumps and can start
computing the flags value sooner.

> +           likely(node == NUMA_NO_NODE || node == numa_mem_id()))
> +               skb = napi_skb_cache_get();
> +       else
> +               skb = kmem_cache_alloc_node(cache, gfp_mask & ~GFP_DMA, node);
>         if (unlikely(!skb))
>                 return NULL;
>         prefetchw(skb);
> @@ -436,7 +441,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
>         __build_skb_around(skb, data, 0);
>         skb->pfmemalloc = pfmemalloc;
>
> -       if (flags & SKB_ALLOC_FCLONE) {
> +       if (clone) {
>                 struct sk_buff_fclones *fclones;
>
>                 fclones = container_of(skb, struct sk_buff_fclones, skb1);
> --
> 2.30.1
>
>