Wireshark · Wireshark-dev: Re: [Wireshark-dev] Memory consumption in tshark

[Evan Huus <eapache@xxxxxxxxx>]

On Tue, Aug 27, 2013 at 5:01 PM, Joerg Mayer <jmayer@xxxxxxxxx> wrote:

On Tue, Aug 27, 2013 at 04:38:08PM -0400, Evan Huus wrote:
> We already discard a great deal of state in (single-pass) tshark that we
> keep around in Wireshark (or two-pass tshark). We do need to keep some,
> though. It's only a bug if we're keeping more than we actually need, and
> that's not determinable from the information we have here. Dario, if you
> could get us a memory profile of tshark in this situation (through
> valgrind's massif tool, for example) that would help us debug further.
>
> I dislike the idea of two-pass by default for exactly this reason: people
> expect tshark to be relatively state-less. This is already not the case,
> but it's a lot worse in two-pass mode. It might even make sense to add a
> --state-less flag to tshark that disables all options which require state.
> I don't know how feasible that would be however.

IIRC, two-pass allows for most/all of the reassembly/request-response stuff,
which we want to do sometimes. Any ideas why we have to keep some information
indefinitely?

Two-pass requires us to keep *all* the state around through the first pass so that it is available during the second pass (at which point it can be discarded).  Even in single-pass mode, there is some state that we can't always immediately discard. If I see a fragment of a TCP message then it doesn't make sense to discard that until the other fragments have arrived and been reassembled. If I see a request, I probably need to keep state from that request until the response (which may never show up).

We already do reassembly and a lot of other stateful work in single-pass mode. The only thing two-pass mode provides is the ability to "see the future" (for example, saying: this request has a response 5 packets later).

 

ciao
      jörg


--
Joerg Mayer                                           <jmayer@xxxxxxxxx>
We are stuck with technology when what we really want is just stuff that
works. Some say that should read Microsoft instead of technology.
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