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Date: Tue, 30 Oct 2007 14:26:34 -0700
From: Stephen Hemminger <shemminger@...ux-foundation.org>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
Subject: Re: [PATCH 23/33] netvm: skb processing
On Tue, 30 Oct 2007 17:04:24 +0100
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> In order to make sure emergency packets receive all memory needed to proceed
> ensure processing of emergency SKBs happens under PF_MEMALLOC.
>
> Use the (new) sk_backlog_rcv() wrapper to ensure this for backlog processing.
>
> Skip taps, since those are user-space again.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> include/net/sock.h | 5 +++++
> net/core/dev.c | 44 ++++++++++++++++++++++++++++++++++++++------
> net/core/sock.c | 18 ++++++++++++++++++
> 3 files changed, 61 insertions(+), 6 deletions(-)
>
> Index: linux-2.6/net/core/dev.c
> ===================================================================
> --- linux-2.6.orig/net/core/dev.c
> +++ linux-2.6/net/core/dev.c
> @@ -1976,10 +1976,23 @@ int netif_receive_skb(struct sk_buff *sk
> struct net_device *orig_dev;
> int ret = NET_RX_DROP;
> __be16 type;
> + unsigned long pflags = current->flags;
> +
> + /* Emergency skb are special, they should
> + * - be delivered to SOCK_MEMALLOC sockets only
> + * - stay away from userspace
> + * - have bounded memory usage
> + *
> + * Use PF_MEMALLOC as a poor mans memory pool - the grouping kind.
> + * This saves us from propagating the allocation context down to all
> + * allocation sites.
> + */
> + if (skb_emergency(skb))
> + current->flags |= PF_MEMALLOC;
>
> /* if we've gotten here through NAPI, check netpoll */
> if (netpoll_receive_skb(skb))
> - return NET_RX_DROP;
> + goto out;
Why the change? doesn't gcc optimize the common exit case anyway?
>
> if (!skb->tstamp.tv64)
> net_timestamp(skb);
> @@ -1990,7 +2003,7 @@ int netif_receive_skb(struct sk_buff *sk
> orig_dev = skb_bond(skb);
>
> if (!orig_dev)
> - return NET_RX_DROP;
> + goto out;
>
> __get_cpu_var(netdev_rx_stat).total++;
>
> @@ -2009,6 +2022,9 @@ int netif_receive_skb(struct sk_buff *sk
> }
> #endif
>
> + if (skb_emergency(skb))
> + goto skip_taps;
> +
> list_for_each_entry_rcu(ptype, &ptype_all, list) {
> if (!ptype->dev || ptype->dev == skb->dev) {
> if (pt_prev)
> @@ -2017,6 +2033,7 @@ int netif_receive_skb(struct sk_buff *sk
> }
> }
>
> +skip_taps:
> #ifdef CONFIG_NET_CLS_ACT
> if (pt_prev) {
> ret = deliver_skb(skb, pt_prev, orig_dev);
> @@ -2029,19 +2046,31 @@ int netif_receive_skb(struct sk_buff *sk
>
> if (ret == TC_ACT_SHOT || (ret == TC_ACT_STOLEN)) {
> kfree_skb(skb);
> - goto out;
> + goto unlock;
> }
>
> skb->tc_verd = 0;
> ncls:
> #endif
>
> + if (skb_emergency(skb))
> + switch(skb->protocol) {
> + case __constant_htons(ETH_P_ARP):
> + case __constant_htons(ETH_P_IP):
> + case __constant_htons(ETH_P_IPV6):
> + case __constant_htons(ETH_P_8021Q):
> + break;
Indentation is wrong, and hard coding protocol values as spcial case
seems bad here. What about vlan's, etc?
> + default:
> + goto drop;
> + }
> +
> skb = handle_bridge(skb, &pt_prev, &ret, orig_dev);
> if (!skb)
> - goto out;
> + goto unlock;
> skb = handle_macvlan(skb, &pt_prev, &ret, orig_dev);
> if (!skb)
> - goto out;
> + goto unlock;
>
> type = skb->protocol;
> list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type)&15], list) {
> @@ -2056,6 +2085,7 @@ ncls:
> if (pt_prev) {
> ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
> } else {
> +drop:
> kfree_skb(skb);
> /* Jamal, now you will not able to escape explaining
> * me how you were going to use this. :-)
> @@ -2063,8 +2093,10 @@ ncls:
> ret = NET_RX_DROP;
> }
>
> -out:
> +unlock:
> rcu_read_unlock();
> +out:
> + tsk_restore_flags(current, pflags, PF_MEMALLOC);
> return ret;
> }
>
> Index: linux-2.6/include/net/sock.h
> ===================================================================
> --- linux-2.6.orig/include/net/sock.h
> +++ linux-2.6/include/net/sock.h
> @@ -523,8 +523,13 @@ static inline void sk_add_backlog(struct
> skb->next = NULL;
> }
>
> +extern int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb);
> +
> static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)
> {
> + if (skb_emergency(skb))
> + return __sk_backlog_rcv(sk, skb);
> +
> return sk->sk_backlog_rcv(sk, skb);
> }
>
> Index: linux-2.6/net/core/sock.c
> ===================================================================
> --- linux-2.6.orig/net/core/sock.c
> +++ linux-2.6/net/core/sock.c
> @@ -319,6 +319,24 @@ int sk_clear_memalloc(struct sock *sk)
> }
> EXPORT_SYMBOL_GPL(sk_clear_memalloc);
>
> +#ifdef CONFIG_NETVM
> +int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)
> +{
> + int ret;
> + unsigned long pflags = current->flags;
> +
> + /* these should have been dropped before queueing */
> + BUG_ON(!sk_has_memalloc(sk));
> +
> + current->flags |= PF_MEMALLOC;
> + ret = sk->sk_backlog_rcv(sk, skb);
> + tsk_restore_flags(current, pflags, PF_MEMALLOC);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(__sk_backlog_rcv);
> +#endif
> +
> static int sock_set_timeout(long *timeo_p, char __user *optval, int optlen)
> {
> struct timeval tv;
I am still not convinced that this solves the problem well enough
to be useful. Can you really survive a heavy memory overcommit?
In other words, can you prove that the added complexity causes the system
to survive a real test where otherwise it would not?
--
Stephen Hemminger <shemminger@...ux-foundation.org>
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