[nginx] SSL: single allocation in session cache on 32-bit platforms.
Sergey Kandaurov
pluknet at nginx.com
Thu Oct 13 10:57:07 UTC 2022
details: https://hg.nginx.org/nginx/rev/5244d3b165ff
branches:
changeset: 8078:5244d3b165ff
user: Maxim Dounin <mdounin at mdounin.ru>
date: Wed Oct 12 20:14:40 2022 +0300
description:
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.
diffstat:
src/event/ngx_event_openssl.c | 71 ++++++++++++++----------------------------
src/event/ngx_event_openssl.h | 8 ++--
2 files changed, 28 insertions(+), 51 deletions(-)
diffs (181 lines):
diff -r ec1fa010c3a5 -r 5244d3b165ff src/event/ngx_event_openssl.c
--- a/src/event/ngx_event_openssl.c Wed Oct 12 20:14:39 2022 +0300
+++ b/src/event/ngx_event_openssl.c Wed Oct 12 20:14:40 2022 +0300
@@ -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);
}
diff -r ec1fa010c3a5 -r 5244d3b165ff src/event/ngx_event_openssl.h
--- a/src/event/ngx_event_openssl.h Wed Oct 12 20:14:39 2022 +0300
+++ b/src/event/ngx_event_openssl.h Wed Oct 12 20:14:40 2022 +0300
@@ -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
};
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