Use smaller zlib objects when under memory pressure

We add a compression level argument to tor_zlib_new, and use it to
determine how much memory to allocate for the zlib object.  We use the
existing level by default, but shift to smaller levels for small
requests when we have been over 3/4 of our memory usage in the past
half-hour.

Closes ticket 11791.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/or/relay.h b/src/or/relay.h
index 73c399154d..3bc668374f 100644
--- a/src/or/relay.h
+++ b/src/or/relay.h
@@ -50,6 +50,8 @@ void clean_cell_pool(void);
 void dump_cell_pool_usage(int severity);
 size_t packed_cell_mem_cost(void);
 
+int have_been_under_memory_pressure(void);
+
 /* For channeltls.c */
 void packed_cell_free(packed_cell_t *cell);