changeset 8078:5244d3b165ff

SSL: single allocation in session cache on 32-bit platforms. Given the present typical SSL session sizes, on 32-bit platforms it is now beneficial to store all data in a single allocation, since rbtree node + session id + ASN1 representation of a session takes 256 bytes of shared memory (36 + 32 + 150 = about 218 bytes plus SNI server name). Storing all data in a single allocation is beneficial for SNI names up to about 40 characters long and makes it possible to store about 4000 sessions in one megabyte (instead of about 3000 sessions now). This also slightly simplifies the code.
author Maxim Dounin <mdounin@mdounin.ru>
date Wed, 12 Oct 2022 20:14:40 +0300
parents ec1fa010c3a5
children f106f4a68faf
files src/event/ngx_event_openssl.c src/event/ngx_event_openssl.h
diffstat 2 files changed, 28 insertions(+), 51 deletions(-) [+]
line wrap: on
line diff
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -3794,9 +3794,9 @@ ngx_ssl_session_cache_init(ngx_shm_zone_
  * Typical length of the external ASN1 representation of a session
  * is about 150 bytes plus SNI server name.
  *
- * On 32-bit platforms we allocate separately an rbtree node,
- * a session id, and an ASN1 representation, they take accordingly
- * 64, 32, and 256 bytes.
+ * On 32-bit platforms we allocate an rbtree node, a session id, and
+ * an ASN1 representation in a single allocation, it typically takes
+ * 256 bytes.
  *
  * On 64-bit platforms we allocate separately an rbtree node + session_id,
  * and an ASN1 representation, they take accordingly 128 and 256 bytes.
@@ -3809,7 +3809,8 @@ static int
 ngx_ssl_new_session(ngx_ssl_conn_t *ssl_conn, ngx_ssl_session_t *sess)
 {
     int                       len;
-    u_char                   *p, *id, *cached_sess, *session_id;
+    u_char                   *p, *session_id;
+    size_t                    n;
     uint32_t                  hash;
     SSL_CTX                  *ssl_ctx;
     unsigned int              session_id_length;
@@ -3869,23 +3870,13 @@ ngx_ssl_new_session(ngx_ssl_conn_t *ssl_
     /* drop one or two expired sessions */
     ngx_ssl_expire_sessions(cache, shpool, 1);
 
-    cached_sess = ngx_slab_alloc_locked(shpool, len);
-
-    if (cached_sess == NULL) {
-
-        /* drop the oldest non-expired session and try once more */
-
-        ngx_ssl_expire_sessions(cache, shpool, 0);
-
-        cached_sess = ngx_slab_alloc_locked(shpool, len);
-
-        if (cached_sess == NULL) {
-            sess_id = NULL;
-            goto failed;
-        }
-    }
-
-    sess_id = ngx_slab_alloc_locked(shpool, sizeof(ngx_ssl_sess_id_t));
+#if (NGX_PTR_SIZE == 8)
+    n = sizeof(ngx_ssl_sess_id_t);
+#else
+    n = offsetof(ngx_ssl_sess_id_t, session) + len;
+#endif
+
+    sess_id = ngx_slab_alloc_locked(shpool, n);
 
     if (sess_id == NULL) {
 
@@ -3893,7 +3884,7 @@ ngx_ssl_new_session(ngx_ssl_conn_t *ssl_
 
         ngx_ssl_expire_sessions(cache, shpool, 0);
 
-        sess_id = ngx_slab_alloc_locked(shpool, sizeof(ngx_ssl_sess_id_t));
+        sess_id = ngx_slab_alloc_locked(shpool, n);
 
         if (sess_id == NULL) {
             goto failed;
@@ -3902,30 +3893,25 @@ ngx_ssl_new_session(ngx_ssl_conn_t *ssl_
 
 #if (NGX_PTR_SIZE == 8)
 
-    id = sess_id->sess_id;
-
-#else
-
-    id = ngx_slab_alloc_locked(shpool, session_id_length);
-
-    if (id == NULL) {
+    sess_id->session = ngx_slab_alloc_locked(shpool, len);
+
+    if (sess_id->session == NULL) {
 
         /* drop the oldest non-expired session and try once more */
 
         ngx_ssl_expire_sessions(cache, shpool, 0);
 
-        id = ngx_slab_alloc_locked(shpool, session_id_length);
-
-        if (id == NULL) {
+        sess_id->session = ngx_slab_alloc_locked(shpool, len);
+
+        if (sess_id->session == NULL) {
             goto failed;
         }
     }
 
 #endif
 
-    ngx_memcpy(cached_sess, buf, len);
-
-    ngx_memcpy(id, session_id, session_id_length);
+    ngx_memcpy(sess_id->session, buf, len);
+    ngx_memcpy(sess_id->id, session_id, session_id_length);
 
     hash = ngx_crc32_short(session_id, session_id_length);
 
@@ -3935,9 +3921,7 @@ ngx_ssl_new_session(ngx_ssl_conn_t *ssl_
 
     sess_id->node.key = hash;
     sess_id->node.data = (u_char) session_id_length;
-    sess_id->id = id;
     sess_id->len = len;
-    sess_id->session = cached_sess;
 
     sess_id->expire = ngx_time() + SSL_CTX_get_timeout(ssl_ctx);
 
@@ -3951,10 +3935,6 @@ ngx_ssl_new_session(ngx_ssl_conn_t *ssl_
 
 failed:
 
-    if (cached_sess) {
-        ngx_slab_free_locked(shpool, cached_sess);
-    }
-
     if (sess_id) {
         ngx_slab_free_locked(shpool, sess_id);
     }
@@ -4051,9 +4031,8 @@ ngx_ssl_get_cached_session(ngx_ssl_conn_
 
             ngx_rbtree_delete(&cache->session_rbtree, node);
 
+#if (NGX_PTR_SIZE == 8)
             ngx_slab_free_locked(shpool, sess_id->session);
-#if (NGX_PTR_SIZE == 4)
-            ngx_slab_free_locked(shpool, sess_id->id);
 #endif
             ngx_slab_free_locked(shpool, sess_id);
 
@@ -4141,9 +4120,8 @@ ngx_ssl_remove_session(SSL_CTX *ssl, ngx
 
             ngx_rbtree_delete(&cache->session_rbtree, node);
 
+#if (NGX_PTR_SIZE == 8)
             ngx_slab_free_locked(shpool, sess_id->session);
-#if (NGX_PTR_SIZE == 4)
-            ngx_slab_free_locked(shpool, sess_id->id);
 #endif
             ngx_slab_free_locked(shpool, sess_id);
 
@@ -4190,9 +4168,8 @@ ngx_ssl_expire_sessions(ngx_ssl_session_
 
         ngx_rbtree_delete(&cache->session_rbtree, &sess_id->node);
 
+#if (NGX_PTR_SIZE == 8)
         ngx_slab_free_locked(shpool, sess_id->session);
-#if (NGX_PTR_SIZE == 4)
-        ngx_slab_free_locked(shpool, sess_id->id);
 #endif
         ngx_slab_free_locked(shpool, sess_id);
     }
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -134,14 +134,14 @@ typedef struct ngx_ssl_sess_id_s  ngx_ss
 
 struct ngx_ssl_sess_id_s {
     ngx_rbtree_node_t           node;
-    u_char                     *id;
     size_t                      len;
-    u_char                     *session;
     ngx_queue_t                 queue;
     time_t                      expire;
+    u_char                      id[32];
 #if (NGX_PTR_SIZE == 8)
-    void                       *stub;
-    u_char                      sess_id[32];
+    u_char                     *session;
+#else
+    u_char                      session[1];
 #endif
 };