Hi,
there are some places where httpd uses more memory than necessary,
which can increase cache misses and reduce performance on current
hardware. Things I would like to change:
1) reorder structs to have fewer holes on 64bit arches
httpd.h has this nice comment since the days of 1.3:
/* Things placed at the end of the record to avoid breaking binary
* compatibility. It would be nice to remember to reorder the entire
* record to improve 64bit alignment the next time we need to break
* binary compatibility for some other reason.
*/
Pro: Examples for space savings on 64bit:
request_rec: 704 -> 672 bytes
server_rec: 208 -> 192 bytes
proxy_worker: 264 -> 208 bytes
Con: In some cases reordering the struct members makes the code harder
to read because related members may no longer be grouped together.
Is it worth changing? Would somebody be -1?
(BTW, pahole is useful for finding such structs).
2) Use char instead of int for the module_levels vector in struct
ap_logconfig. The length of the vector is ~100.
Pro: This may save ~300 bytes per server conf which are read often and
therefore occupy CPU-cache memory
Con: On some architectures, accessing chars is slower than accessing
ints.
Does anyone have an idea what is better, here? Int or char?
The same argument could be made for boolean flags in various other
structs. But I don't think those are worth the effort.
3) In server/config.c, many config vectors are created (allocated and
zeroed) with length (total_modules + DYNAMIC_MODULE_LIMIT). But this
is only necessary before dynamic modules are loaded. Afterwards,
total_modules is set to the total number of modules. Therefore
allocating a vec of length total_modules should be enough. This would
save zeroing 128 pointers per request and connection.
It seems the attached patch works and I could not find any problems
when adding/removing modules during graceful restart. Objections?
Cheers,
Stefan
diff --git a/server/config.c b/server/config.c
index 0f1660a..dfaac61 100644
--- a/server/config.c
+++ b/server/config.c
@@ -210,6 +210,7 @@ typedef void *(*merger_func)(apr_pool_t *, void *, void *);
* overridden).
*/
+/* for use before dynamic modules are loaded */
static ap_conf_vector_t *create_empty_config(apr_pool_t *p)
{
void *conf_vector = apr_pcalloc(p, sizeof(void *) *
@@ -217,6 +218,13 @@ static ap_conf_vector_t *create_empty_config(apr_pool_t *p)
return conf_vector;
}
+/* for use after dynamic modules are loaded */
+static ap_conf_vector_t *create_short_empty_config(apr_pool_t *p)
+{
+ void *conf_vector = apr_pcalloc(p, sizeof(void *) * total_modules);
+ return conf_vector;
+}
+
static ap_conf_vector_t *create_default_per_dir_config(apr_pool_t *p)
{
void **conf_vector = apr_pcalloc(p, sizeof(void *) *
@@ -299,17 +307,17 @@ static void merge_server_configs(apr_pool_t *p, ap_conf_vector_t *base,
AP_CORE_DECLARE(ap_conf_vector_t *) ap_create_request_config(apr_pool_t *p)
{
- return create_empty_config(p);
+ return create_short_empty_config(p);
}
AP_CORE_DECLARE(ap_conf_vector_t *) ap_create_conn_config(apr_pool_t *p)
{
- return create_empty_config(p);
+ return create_short_empty_config(p);
}
AP_CORE_DECLARE(ap_conf_vector_t *) ap_create_per_dir_config(apr_pool_t *p)
{
- return create_empty_config(p);
+ return create_short_empty_config(p);
}
/* Invoke the filter_init_func for all filters with FILTERS where f->r
@@ -1364,7 +1372,7 @@ AP_DECLARE(void) ap_reset_module_loglevels(struct ap_logconf *l, int val)
{
if (l->module_levels) {
int i;
- for (i = 0; i < total_modules + DYNAMIC_MODULE_LIMIT; i++)
+ for (i = 0; i < total_modules; i++)
l->module_levels[i] = val;
}
}
@@ -1373,8 +1381,7 @@ AP_DECLARE(void) ap_set_module_loglevel(apr_pool_t *pool, struct ap_logconf *l,
int index, int level)
{
if (!l->module_levels) {
- l->module_levels = apr_palloc(pool,
- sizeof(int) * (total_modules + DYNAMIC_MODULE_LIMIT));
+ l->module_levels = apr_palloc(pool, sizeof(int) * total_modules);
if (l->level == APLOG_UNSET) {
ap_reset_module_loglevels(l, APLOG_UNSET);
}
@@ -2002,7 +2009,7 @@ AP_CORE_DECLARE(const char *) ap_init_virtual_host(apr_pool_t *p,
s->names = apr_array_make(p, 4, sizeof(char **));
s->wild_names = apr_array_make(p, 4, sizeof(char **));
- s->module_config = create_empty_config(p);
+ s->module_config = create_short_empty_config(p);
s->lookup_defaults = ap_create_per_dir_config(p);
s->limit_req_line = main_server->limit_req_line;
@@ -2022,8 +2029,7 @@ AP_DECLARE(struct ap_logconf *) ap_new_log_config(apr_pool_t *p,
l->level = old->level;
if (old->module_levels) {
l->module_levels =
- apr_pmemdup(p, old->module_levels,
- sizeof(int) * (total_modules + DYNAMIC_MODULE_LIMIT));
+ apr_pmemdup(p, old->module_levels, sizeof(int) * total_modules);
}
}
else {
@@ -2048,7 +2054,7 @@ AP_DECLARE(void) ap_merge_log_config(const struct ap_logconf *old,
}
else if (old->module_levels != NULL) {
int i;
- for (i = 0; i < total_modules + DYNAMIC_MODULE_LIMIT; i++) {
+ for (i = 0; i < total_modules; i++) {
if (new->module_levels[i] == APLOG_UNSET)
new->module_levels[i] = old->module_levels[i];
}
