linux - 为什么两个不同系统之间的 apache2 中每个进程使用的内存差异如此之大？

Question

我有一对 Ubuntu 专用服务器...
服务器1:

Ubuntu 16.04.7 (64 bits)
16GB RAM
8 Xeon CPU
Apache 2.4.18
MPM mode: prefork

服务器2:

Ubuntu server 20.04.2 (64 bits)
32GB RAM
8 Xeon CPU
2.4.41
MPM mode: event

在 Server1 上，每个 apache2 进程使用 7MB 到 18MB 的 RAM ...

ps axo 'user rss cmd' | grep apache | grep -v "\(root\|grep\|tomcat\)"
www-data 18232 /usr/sbin/apache2 -k start
www-data 11700 /usr/sbin/apache2 -k start
www-data 11276 /usr/sbin/apache2 -k start
www-data 10792 /usr/sbin/apache2 -k start
www-data 11216 /usr/sbin/apache2 -k start
www-data 11600 /usr/sbin/apache2 -k start
www-data 10336 /usr/sbin/apache2 -k start
www-data 11356 /usr/sbin/apache2 -k start
www-data 11348 /usr/sbin/apache2 -k start
www-data 10980 /usr/sbin/apache2 -k start
www-data 11316 /usr/sbin/apache2 -k start
www-data  6808 /usr/sbin/apache2 -k start

在 Server2 上，每个 apache2 进程使用 120MB 到 130MB 的 RAM ...

ps axo 'user rss cmd' | grep apache | grep -v "\(root\|grep\|tomcat\)"
www-data 120436 /usr/sbin/apache2 -k start
www-data 119784 /usr/sbin/apache2 -k start
www-data 128720 /usr/sbin/apache2 -k start
www-data 130208 /usr/sbin/apache2 -k start

为什么使用的内存差异如此之大？
在阅读了一些文档和谷歌之后，我想到了加载模块，但每个服务器之间没有太大区别......
服务器1

# apache2 -M                 
Loaded Modules:
 core_module (static)
 so_module (static)
 watchdog_module (static)
 http_module (static)
 log_config_module (static)
 logio_module (static)
 version_module (static)
 unixd_module (static)
 access_compat_module (shared)
 actions_module (shared)
 alias_module (shared)
 auth_basic_module (shared)
 auth_digest_module (shared)
 auth_openidc_module (shared)
 authn_core_module (shared)
 authn_file_module (shared)
 authz_core_module (shared)
 authz_host_module (shared)
 authz_user_module (shared)
 autoindex_module (shared)
 bw_module (shared)
 cgi_module (shared)
 dav_module (shared)
 dav_fs_module (shared)
 dav_lock_module (shared)
 deflate_module (shared)
 dir_module (shared)
 env_module (shared)
 expires_module (shared)
 fcgid_module (shared)
 filter_module (shared)
 headers_module (shared)
 include_module (shared)
 mime_module (shared)
 mpm_prefork_module (shared)
 negotiation_module (shared)
 proxy_module (shared)
 proxy_balancer_module (shared)
 proxy_fcgi_module (shared)
 proxy_http_module (shared)
 rewrite_module (shared)
 setenvif_module (shared)
 slotmem_shm_module (shared)
 socache_shmcb_module (shared)
 ssl_module (shared)
 status_module (shared)
 suexec_module (shared)
 userdir_module (shared)

服务器2

# apache2 -M
Loaded Modules:
 core_module (static)
 so_module (static)
 watchdog_module (static)
 http_module (static)
 log_config_module (static)
 logio_module (static)
 version_module (static)
 unixd_module (static)
 access_compat_module (shared)
 aclr_module (shared)
 actions_module (shared)
 alias_module (shared)
 auth_basic_module (shared)
 auth_digest_module (shared)
 auth_openidc_module (shared)
 authn_core_module (shared)
 authn_file_module (shared)
 authz_core_module (shared)
 authz_host_module (shared)
 authz_user_module (shared)
 autoindex_module (shared)
 cgid_module (shared)
 dav_module (shared)
 dav_fs_module (shared)
 dav_lock_module (shared)
 deflate_module (shared)
 dir_module (shared)
 env_module (shared)
 fcgid_module (shared)
 filter_module (shared)
 headers_module (shared)
 include_module (shared)
 mime_module (shared)
 mpm_event_module (shared)
 negotiation_module (shared)
 proxy_module (shared)
 proxy_balancer_module (shared)
 proxy_fcgi_module (shared)
 proxy_http_module (shared)
 remoteip_module (shared)
 reqtimeout_module (shared)
 rewrite_module (shared)
 security2_module (shared)
 setenvif_module (shared)
 slotmem_shm_module (shared)
 socache_shmcb_module (shared)
 ssl_module (shared)
 status_module (shared)
 suexec_module (shared)
 unique_id_module (shared)
 userdir_module (shared)

我已经在 Server2 上将 MPM 模式从 Event 更改为 Prefork，结果相同。
我还能检查什么来理解这种差异？

Answer 1

问题出在模块 security2 上。
启用模块(每个进程 120-160MB)...

# ps axo 'user rss cmd' | grep apache | grep -v "\(root\|grep\|tomcat\)"
www-data 121232 /usr/sbin/apache2 -k start
www-data 120596 /usr/sbin/apache2 -k start
www-data 156816 /usr/sbin/apache2 -k start
www-data 162668 /usr/sbin/apache2 -k start

禁用模块(每个进程 9-15MB)...

# a2dismod security2
Module security2 disabled.
To activate the new configuration, you need to run:
  systemctl restart apache2
# systemctl restart apache2
# ps axo 'user rss cmd' | grep apache | grep -v "\(root\|grep\|tomcat\)"
www-data 10340 /usr/sbin/apache2 -k start
www-data  9764 /usr/sbin/apache2 -k start
www-data 14164 /usr/sbin/apache2 -k start
www-data 14220 /usr/sbin/apache2 -k start

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