[tor-bugs] #9686 [Tor]: MaxMemInCellQueues minimum of 500MB is too large for low-RAM relays (Raspberry Pi)

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#9686: MaxMemInCellQueues minimum of 500MB is too large for low-RAM relays
(Raspberry Pi)
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 Reporter:  gmorehouse  |          Owner:
     Type:  defect      |         Status:  new
 Priority:  normal      |      Milestone:
Component:  Tor         |        Version:
 Keywords:  tor-relay   |  Actual Points:
Parent ID:              |         Points:
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 This is related to #9646.

 Based on discussion in that ticket, I attempted to set my
 MaxMemInCellQueues to 384MB on my Raspberry Pi relay, which has a hardware
 maximum of 512MB RAM (and boots with about 485MB usable physical memory
 when running Raspbian).

 This results in the following error:

   `[warn] MaxMemInCellQueues must be at least 500 MB for now. Ideally,
 have it as large as you can afford.`

 Ideally, this setting would be flexible, and allow lower values, possibly
 calculated as some percentage of total available physical memory (or
 possibly not, depending on how much time you'd like to spend mucking with
 it).

 If Tor has 500MB in cell queues on a 512MB Raspberry Pi, though, the Pi is
 already guaranteed to be hitting swap if the out-of-memory killer hasn't
 already come around to 'fix' things.  I took a complete guess at 384MB as
 a reasonable value for a machine that boots with 485MB free.

 Under non-botnet network conditions, a Raspberry Pi can happily sustain
 ''at least'' 2 to 3 Mbps of traffic as a relay, and that's without
 extensive tuning.  I think it's worth the effort to keep these low-cost,
 low-resource, physically small boxes in mind when working on Tor, as many
 of them scattered around the world would be a fairly easy accomplishment
 and might do a lot to beef up the network.

 Also, the libgcrypt folks have been working hard in the last 30 days on
 ARM assembly language implementations of algorithms which Tor uses[1]; if
 you assume these implementations will eventually cross-pollinate into
 libraries used by Tor, a Raspberry Pi may one day be able to relay a lot
 more than 2-3Mbps.

 1.
 http://gnupg.10057.n7.nabble.com/template/NamlServlet.jtp?macro=search_page&node=27394&query=arm&days=30

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9686>
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