linux-kernel - Re: [RFC PATCH net-next] Introducing lockless cache built on top of slab allocator

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Date:   Mon, 20 Sep 2021 13:50:27 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Kangmin Park <l4stpr0gr4m@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexander Lobakin <alobakin@...me>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Guillaume Nault <gnault@...hat.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Cong Wang <cong.wang@...edance.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next] Introducing lockless cache built on top of
 slab allocator

On Tue, 21 Sep 2021 02:47:13 +0900 Kangmin Park wrote:
> It is just introducing and proof of concept.
> The patch code is based on other RFC patches. So, the code is not
> correct yet, it is just simple proof of concept.
> 
> Recently block layer implemented percpu, lockless cache on the top
> of slab allocator. It can be used for IO polling.
> 
> Link: https://lwn.net/Articles/868070/
> Link: https://www.spinics.net/lists/linux-block/msg71964.html
> 
> It gained some IOPS increase (performance increased by about 10%
> on the block layer).
> 
> And there are attempts to implement the percpu, lockless cache.
> 
> Link: https://lore.kernel.org/linux-mm/20210920154816.31832-1-42.hyeyoo@gmail.com/T/#u
> 
> If this cache is implemented successfully,
> how about use this cache to allocate skb instead of kmem_cache_alloc_bulk()
> in napi_skb_cache_get()?
> 
> I want your comment/opinion.

Please take a look at skb cache in struct napi_alloc_cache.
That should be your target here.

> Signed-off-by: Kangmin Park <l4stpr0gr4m@...il.com>
> ---
>  net/core/skbuff.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 7c2ab27fcbf9..f9a9deca423d 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -170,11 +170,15 @@ static struct sk_buff *napi_skb_cache_get(void)
>  	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
>  	struct sk_buff *skb;
>  
> -	if (unlikely(!nc->skb_count))
> -		nc->skb_count = kmem_cache_alloc_bulk(skbuff_head_cache,
> -						      GFP_ATOMIC,
> -						      NAPI_SKB_CACHE_BULK,
> -						      nc->skb_cache);
> +	if (unlikely(!nc->skb_count)) {
> +		/* kmem_cache_alloc_cached should be changed to return the size of
> +		 * the allocated cache
> +		 */
> +		nc->skb_cache = kmem_cache_alloc_cached(skbuff_head_cache,
> +							GFP_ATOMIC | SLB_LOCKLESS_CACHE);
> +		nc->skb_count = this_cpu_ptr(skbuff_head_cache)->size;
> +	}
> +
>  	if (unlikely(!nc->skb_count))
>  		return NULL;
>