netdev - Re: [PATCH] net: No more expensive sock_hold()/sock

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Date:	Wed, 10 Jun 2009 01:17:43 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	rusty@...tcorp.com.au, netdev@...r.kernel.org
Subject: Re: [PATCH] net: No more expensive sock_hold()/sock_put() on each
 tx

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 04 Jun 2009 11:18:35 +0200

> @@ -1172,12 +1186,18 @@ void __init sk_init(void)
>  void sock_wfree(struct sk_buff *skb)
>  {
>  	struct sock *sk = skb->sk;
> +	int res;
>  
>  	/* In case it might be waiting for more memory. */
> -	atomic_sub(skb->truesize, &sk->sk_wmem_alloc);
> +	res = atomic_sub_return(skb->truesize, &sk->sk_wmem_alloc);
>  	if (!sock_flag(sk, SOCK_USE_WRITE_QUEUE))
>  		sk->sk_write_space(sk);
> -	sock_put(sk);
> +	/*
> +	 * if sk_wmem_alloc reached 0, we are last user and should
> +	 * free this sock, as sk_free() call could not do it.
> +	 */
> +	if (res == 0)
> +		__sk_free(sk);
>  }
>  EXPORT_SYMBOL(sock_wfree);
>  

Eric, I don't understand this part, please enlighten me :-)

Just because we've liberated all of the write buffer space, that does
not mean that it's time to kill off the socket completely.

Right?
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