On Tue, 2007-01-16 at 16:25 +0300, Evgeniy Polyakov wrote:

On Tue, Jan 16, 2007 at 10:46:06AM +0100, Peter Zijlstra (a.p.zijlstra@chello.nl) wrote:

quoted

@@ -1767,10 +1767,23 @@ 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_VMIO 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 (unlikely(skb->emergency))
+		current->flags |= PF_MEMALLOC;

Access to 'current' in netif_receive_skb()???
Why do you want to work with, for example keventd?

Can this run in keventd?

I thought this was softirq context and thus this would either run in a
borrowed context or in ksoftirqd. See patch 3/9.

quoted

@@ -1798,6 +1811,8 @@ int netif_receive_skb(struct sk_buff *sk
 		goto ncls;
 	}
 #endif
+	if (unlikely(skb->emergency))
+		goto skip_taps;
 
 	list_for_each_entry_rcu(ptype, &ptype_all, list) {
 		if (!ptype->dev || ptype->dev == skb->dev) {

@@ -1807,6 +1822,7 @@ int netif_receive_skb(struct sk_buff *sk
 		}
 	}
 
+skip_taps:

It is still a 'tap'.

Not sure what you are saying, I thought this should stop delivery of
skbs to taps?

quoted

 #ifdef CONFIG_NET_CLS_ACT
 	if (pt_prev) {
 		ret = deliver_skb(skb, pt_prev, orig_dev);

@@ -1819,15 +1835,26 @@ 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 (unlikely(skb->emergency))
+		switch(skb->protocol) {
+			case __constant_htons(ETH_P_ARP):
+			case __constant_htons(ETH_P_IP):
+			case __constant_htons(ETH_P_IPV6):
+				break;

Poor vlans and appletalk.

Yeah and all those other too, maybe some day.

quoted

Index: linux-2.6-git/net/ipv4/tcp_ipv4.c
===================================================================

--- linux-2.6-git.orig/net/ipv4/tcp_ipv4.c	2007-01-12 12:20:07.000000000 +0100
+++ linux-2.6-git/net/ipv4/tcp_ipv4.c	2007-01-12 12:21:14.000000000 +0100

@@ -1604,6 +1604,22 @@ csum_err:
 	goto discard;
 }
 
+static int tcp_v4_backlog_rcv(struct sock *sk, struct sk_buff *skb)
+{
+	int ret;
+	unsigned long pflags = current->flags;
+	if (unlikely(skb->emergency)) {
+		BUG_ON(!sk_has_vmio(sk)); /* we dropped those before queueing */
+		if (!(pflags & PF_MEMALLOC))
+			current->flags |= PF_MEMALLOC;
+	}
+
+	ret = tcp_v4_do_rcv(sk, skb);
+
+	current->flags = pflags;
+	return ret;

Why don't you want to just setup PF_MEMALLOC for the socket and all
related processes?

I'm not understanding what you're saying here.

I want grant the processing of skb->emergency packets access to the
memory reserves.

How would I set PF_MEMALLOC on a socket, its a process flag? And which
related processes?

quoted

+}
+
 /*
  *	From tcp_input.c
  */

@@ -1654,6 +1670,15 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	if (!sk)
 		goto no_tcp_socket;
 
+	if (unlikely(skb->emergency)) {
+	       	if (!sk_has_vmio(sk))
+			goto discard_and_relse;
+		/*
+		   decrease window size..
+		   tcp_enter_quickack_mode(sk);
+		*/

How does this decrease window size?
Maybe ack scheduling would be better handled by inet_csk_schedule_ack()
or just directly send an ack, which in turn requires allocation, which
can be bound to this received frame processing...

It doesn't, I thought that it might be a good idea doing that, but never
got around to actually figuring out how to do it.