[tor-bugs] #9093 [Tor]: We should have better, fairer OOM handling

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#9093: We should have better, fairer OOM handling
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 Reporter:  nickm                   |          Owner:                    
     Type:  enhancement             |         Status:  new               
 Priority:  major                   |      Milestone:  Tor: 0.2.5.x-final
Component:  Tor                     |        Version:                    
 Keywords:  tor-relay 024-backport  |         Parent:                    
   Points:                          |   Actualpoints:                    
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 With our second attempt at a #9063 fix, merged into 0.2.4.14-alpha, I
 introduced an OOM handler that kills circuits if we're too low on memory.
 But the obvious algorithm I used ("Algorithm 1" as described on #9072) is
 not as good as it could be or should be.

 Currently, I favor looking for a good estimator of "How long will this
 circuit take to drain all of its currently queued cells?" and using that
 for deciding which circuits to kill when low on RAM.  There are other
 suggestions on #9072 too.  And to those a suggestion from IRC that we look
 at the age of the oldest cell on the circuit.

 If we find something that uses data that Tor currently captures (for
 example, with the ewma machinery), it will be much easier to deploy.

 For whatever we pick, we need to analyze its security implications and
 look for ways to game it to provoke relays to do something stupid.

 It would be good to have a default OOM threshold computed in some sane
 (though probably nonportable) way based on available RAM, with a
 reasonable cap.  That might be ridiculously hard though.

 It would also be good to see about taking more potentially-big things into
 account, not just circuit queues.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9093>
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