Need help trouble shooting high CPU usage by PHP-fpm
Try using strace -p 26721 to see what the process is doing. To see which file handle is which use lsof -p 26721.
You could start by reducing Google and Bing requests... Have you set up a robots.txt? Exclude the ScriptPath from crawling, so that only the canonical page URLs are indexed, but not any URL with parameters to api.php or index.php. Also set a crawl-delay if needed.
Many MediaWiki sites are slowed down by search engines due to small configuration errors.