Releasing memory of idle SSL connection. This saves about 34K per SSL
connection. The SSL_MODE_RELEASE_BUFFERS option is available since
OpenSSL 1.0.0d.

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index aa9a4c9..bbec1db 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -179,6 +179,10 @@
     SSL_CTX_set_options(ssl->ctx, SSL_OP_NO_COMPRESSION);
 #endif
 
+#ifdef SSL_MODE_RELEASE_BUFFERS
+    SSL_CTX_set_mode(ssl->ctx, SSL_MODE_RELEASE_BUFFERS);
+#endif
+
     SSL_CTX_set_read_ahead(ssl->ctx, 1);
 
     SSL_CTX_set_info_callback(ssl->ctx, ngx_ssl_info_callback);