RE: [patch v1, kernel version 3.2.1] net/ipv4/ip_gre: Ethernet multipoint GRE over IP

quoted

+	for (i = 0; i < GRETAP_BR_HASH_SIZE; i++) {
+		struct ipgre_tap_bridge_entry *entry;
+		struct hlist_node *h, *n;
+		hlist_for_each_entry_safe(entry, h, n,
+			&tunnel->hash[i], hlist)
+		{
+			unsigned long this_timer;
+			this_timer = entry->ageing_timer + delay;
+			if (time_before_eq(this_timer, jiffies))
+				ipgre_tap_bridge_delete(entry);
+			else if (time_before(this_timer, next_timer))
+				next_timer = this_timer;
+		}
+	}
+	spin_unlock_bh(&tunnel->hash_lock);
+	mod_timer(&tunnel->gc_timer, round_jiffies(next_timer + HZ/4));

wow... why setup a 250 ms timer, if entries are valid 300 seconds ?

Isn't that code trying to wakeup 250ms after the first expiry of any
of its items?

Do you even need a timer at all?

It may be enough to just put a timestamp into each entry
and tidy up when scanning one of the hash chains in (say)
the 'add item' path - when you need write access anyway.

A hash table might not be the best structure either!
The hash lookup is still o(n) for n >> table_size.
It also may be likely that you'll do repeated lookups for a small
number of items - in which case using a hash to cache recent lookups
might be useful (maybe with some type of balanced tree structure)

	David