Re: [PATCH RFC] inetpeer: remove AVL implementation in favor of RB tree

From: Eric Dumazet <edumazet@google.com>

As discussed in Faro during Netfilter Workshop 2017, RB trees can be
used with RCU, using a seqlock.

Note that net/rxrpc/conn_service.c is already using this.

This patch converts inetpeer from AVL tree to RB tree, since it allows
to remove private AVL code in favor of shared RB code.

$ size net/ipv4/inetpeer.before net/ipv4/inetpeer.after
   text	   data	    bss	    dec	    hex	filename
   3195	     40	    128	   3363	    d23	net/ipv4/inetpeer.before
   1562	     24	      0	   1586	    632	net/ipv4/inetpeer.after

The same technique can be used to speed up
net/netfilter/nft_set_rbtree.c

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 
 	return p;

@@ -467,8 +231,9 @@ EXPORT_SYMBOL_GPL(inet_getpeer);
 void inet_putpeer(struct inet_peer *p)
 {
 	p->dtime = (__u32)jiffies;
-	smp_mb__before_atomic();
-	refcount_dec(&p->refcnt);
+
+	if (refcount_dec_and_test(&p->refcnt))