On 22 Jul 2017, at 20:45, Felix zwiebel@quantentunnel.de wrote:

Hi everybody

I observed two circuit bursts around July 19th. On a poor server Tor crashed, on a strong it didn't. The logs below are from the crashed one.

I'm on FreeBSD. To my mind the circuit burst exhausts the nmbclusters (not memory, Inact tells). Strong servers have more. How long is more enough ? On FreeBSD nmbclusters is a boot tunable.

So increase kern.ipc.nmbclusters on your machine?

Using the calculations in 11.11.2. Network Limits in: https://www.freebsd.org/doc/en/books/handbook/configtuning-kernel-limits.htm...

Tor uses a 16kB send and receive buffer by default. There are ~7000 relays in the network, plus client and exit connections. (Your relay is connected to about 5500 relays and clients/internet servers.) But let's say there are 1000 client connections on Guards, and 10000 exit connections on Exits.

So for a Guard, you want 8,000 * (16kB + 16kB) * 2 / 2kB = 256,000 mbufs And for an Exit, you want 17,000 * (16kB + 16kB) * 2 / 2kB = 544,000 mbufs

The exact figures will depend on your relay's bandwidth weights. You should probably try doubling the current setting, until the issue goes away.

Of course, if you don't have 512MB or 1GB of spare RAM for your kernel, then you'll want to tune Tor instead.

The strong server took 140k circuits for several hours.

Is it worth thinking about a Tor setting like MaxCircuitsPerTime ? MaxAdvertisedBandwidth won't help directly.

If you want to tune tor, if you're concerned about socket buffers, try:

ConstrainedSockets ConstrainedSockSize

Or open sockets:

ConnLimit

If you're concerned about pending circuits or data, try:

MaxClientCircuitsPending MaxOnionQueueDelay MaxMemInQueues

1. Normal operation

kern.openfiles: 5516 Mem: 36M Active, 1288M Inact, 455M Wired, 1452K Cache, 425M Buf, 191M Free Swap: 3072M Total, 3072M Free USERNAME PRI NICE SIZE RES STATE TIME CPU COMMAND _tor 87 0 309M 283M RUN 125.7H 50.00% tor{tor} _tor 22 0 309M 283M uwait 167:32 3.96% tor{tor}

2. Last minute before crash:

kern.openfiles: 5467 Mem: 296M Active, 935M Inact, 692M Wired, 21M Cache, 425M Buf, 27M Free Swap: 3072M Total, 1592K Used, 3070M Free USERNAME PRI NICE SIZE RES STATE TIME CPU COMMAND _tor 85 0 465M 438M RUN 126.8H 43.99% tor{tor} _tor 33 0 465M 438M uwait 186:39 15.97% tor{tor}

3. Crashed:

kern.openfiles: 5455 Mem: 295M Active, 936M Inact, 699M Wired, 21M Cache, 425M Buf, 21M Free Swap: 3072M Total, 1592K Used, 3070M Free kernel: [zone: mbuf_cluster] kern.ipc.nmbclusters limit reached

sysctl kern.ipc.nmbclusters 126138

Heartbeat: Tor's uptime is 15 days 16:00 hours, with 1611 circuits Heartbeat: Tor's uptime is 15 days 17:00 hours, with 40471 circuits Heartbeat: Tor's uptime is 15 days 18:00 hours, with 88052 circuits Heartbeat: Tor's uptime is 15 days 19:00 hours, with 78444 circuits [warn] Your computer is too slow to handle this many circuit creation requests! Please consider using the MaxAdvertisedBandwidth config option or choosing a more restricted exit policy.

T

-- Tim Wilson-Brown (teor)

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