cvs commit: src/sys/netgraph/netflow ng_netflow.c

Gleb Smirnoff glebius at
Tue Feb 5 06:17:37 PST 2008

On Sun, Feb 03, 2008 at 11:36:49AM -0500, Louis Mamakos wrote:
L> > Gleb Smirnoff пишет:
L> >>  you should have asked me for review before committing! This is
L> >> not a bug, this is a feature. This was quite clear from the comments,
L> >> that you removed:
L> >> -       /* if export hook disconnected stop running expire(). */
L> >>  This is intended behavior. We must not lose information unless
L> >> user explicitly wants to lose information. In the latter case
L> >> he will connect ng_hole(4) node to the "export" hook. But we must
L> >> not lose information if user runs some script that swaps receiving
L> >> node on the "export" hook.
L> >>  Please backout this change!
L> >
L> > Expire process was not depending completely on connected hook even before 
L> > this commit. For example, every TCP session closing forces some data 
L> > export. So even with export hook disconnected some data still will be lost 
L> > and not just lost, but it was leading to memory leak which I have fixed 
L> > with other commit.

That's true. The active TCP close should be reworked. And the new active expiry
feature violates the original design, when no export hook ment, no data lose. :(

L>  If there's a concern about no losing the netflow data, then it's likely that 
L>  it's usually the case that an export hook is connected.  If a user wanted to 
L>  change the export arrangement for the netflow data, then just disconnected 
L>  and reconnecting to the export hook won't caused data to be lost if the 
L>  expiry parameters are set to something reasonable.

Since expiry runs periodically, then it can race with hook change

L>  Finally, in the absence of infinite amounts of memory, data will eventually 
L>  be lost.  The only decision is over what duration data should be kept around 
L>  so that it might be harvested.  It's a huge surprise that the netflow module 
L>  consumes large amounts of kernel memory.  As a user, I expected the 
L>  expiration timers to be the policy that I specify to control how long the 
L>  netflow stats are stored, and my expectation wasn't met.

Huge surprise? How can you expect a kernel module that stores a lot of data
consume a little kernel memory?

I agree that the behavior should be documented in manual page and using
ng_hole(4) for your case should be advised. If you send me a manual page patch,
I can commit it.

Totus tuus, Glebius.

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