Messages in this thread | | | Date | Thu, 01 Sep 2005 23:28:23 -0700 (PDT) | Subject | Re: Possible BUG in IPv4 TCP window handling, all recent 2.4.x/2.6.x kernels | From | "David S. Miller" <> |
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From: John Heffner <jheffner@psc.edu> Date: Thu, 1 Sep 2005 22:51:48 -0400
> I have an idea why this is going on. Packets are pre-allocated by the > driver to be a max packet size, so when you send small packets, it > wastes a lot of memory. Currently Linux uses the packets at the > beginning of a connection to make a guess at how best to advertise its > window so as not to overflow the socket's memory bounds. Since you > start out with big segments then go to small ones, this is defeating > that mechanism. It's actually documented in the comments in > tcp_input.c. :) > > * The scheme does not work when sender sends good segments opening > * window and then starts to feed us spagetti. But it should work > * in common situations. Otherwise, we have to rely on queue collapsing.
That's a strong possibility, good catch John.
Although, I'm still not ruling out some box in the middle even though I consider it less likely than your theory.
So you're suggesting that tcp_prune_queue() should do the:
if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) tcp_clamp_window(sk, tp);
check after attempting to collapse the queue.
But, that window clamping should fix the problem, as we recalculate the window to advertise. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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