The open_file_cache_* options in nginx (but other server have similar options) allows to cache in memory the file so the disk is used only when the cached value

The open_file_cache_* options in nginx (but other server have similar options) allows to cache in memory the file so the disk is used only when the cached value is no more valid (timed to 30s lifetime on the linked tests). After a quick refresh of how the buffer cache works, i'd say that you are correct and that with the option above the server is also using a simpler data structure to retrieve those cached pages (no blocks list to traverse, no access locks). The difference in performance with and without this option was huge in a quick test, enabling the server caching i saw the number of req/s increase 400%-500%.