commit 7976eb12bd3138a8b9d666d4be393e1095bd620d Author: Nick Mathewson nickm@torproject.org Date: Sun Jan 4 17:41:36 2015 -0500

Document the OOM algorithm in tor-spec. (#13794) --- tor-spec.txt | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+)

diff --git a/tor-spec.txt b/tor-spec.txt index 1c1257b..cf54271 100644 --- a/tor-spec.txt +++ b/tor-spec.txt @@ -1559,3 +1559,31 @@ see tor-design.pdf. ten cell payloads remaining to be flushed at that edge.

+ +8. Handling resource exhaustion + + +8.1. Memory exhaustion. + + If RAM becomes low, an OR should begin destroying circuits until + more memory is free again. We recommend the following algorithm: + + - Set a threshold amount of RAM to recover at 10% of the total RAM. + + - Sort the circuits by their 'staleness', defined as the age of the + oldest data queued on the circuit. This data can be: + + * Bytes that are waiting to flush to or from a stream on that + circuit. + + * Bytes that are waiting to flush from a connection created with + BEGIN_DIR. + + * Cells that are waiting to flush or be processed. + + - While we have not yet recovered enough RAM: + + * Free all memory held by the most stale circuit, and send DESTROY + cells in both directions on that circuit. Count the amount of + memory we recovered towards the total. +