Messages in this thread | | | Date | Tue, 01 Dec 2009 11:28:50 -0600 | From | "Chris Friesen" <> | Subject | Re: seeing strange values for tcp sk_rmem_alloc |
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On 12/01/2009 10:58 AM, Eric Dumazet wrote:
> Me wondering why you think sk_rmem_alloc is about TX side. > Its used in RX path. rmem means ReadMemory.
Yep, I realize this.
> You can send 1 Gbytes of data, and sk_rmem_alloc doesnt change, if your > TCP stream is unidirectionnal. > > sk_rmem_alloc grows when skb are queued into receive queue > sk_rmem_alloc shrinks when application reads this receive queue.
I realize this. I sent the data from a socket to itself. It could just as easily be done with two tcp sockets. The important thing is that I control both the tx and rx sides, so I know how much data should be present in the rx queue at any point in time.
The part that surprised me was that I could send multiple chunks of data without sk_rmem_alloc changing on the socket to which the data was being sent. Then it would jump up by a large amount (up to 20K) all at once.
I'm starting to suspect that the discrepency might have something to do with the skb_copy_datagram_iovec() call in tcp_data_queue(), and how skb_set_owner_r() is only called if "eaten" is <= 0. This could be totally off-base though.
Chris
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