Emacs User Configuration Optimization -

Main Idea

We need to get the Emacs's startup log
Analyze the log,and find the packages do not need to be loaded in the Emacs startup phase.
Lazy load the packages

Get Startup Log

How to use it

You must install it first, choose any way you prefer. Notice: You need to load and active benchmark-init as soon as possible. I put it in my early-init.el file.

It gives us two show command

benchmark-init/show-durations-tabulated: find the most spending time packages in the startup phase.
benchmark-init/show-durations-tree: find the dependent relationship of the packages, and the order of the packages loaded.

to simply I call they as table and tree respectively.

Analyze Log

use table find the most spending time package.
use tree find when you load the package. If you split the configuration file, you can find the closest .el file in upward direction, which loads the package.
If you are unfamiliar with the package, try to search it on the Internet and understand the importance of the package.
choose a strategy and apply it to the package:
1. Remove: If you do not need the package right now, then just delete/comment it.
2. Not thing change: When you need it loaded in the startup phase.
3. Lazy load: When you need it but not in the startup phase.

Find the Dependent Files

When I find a package not in my configuration files, I usually use the way to find the dependent files of the package.

  (defun search-dependent-files (package)
    (require 'loadhist)
    (file-dependents (feature-file package)))

  (search-dependent-files 'consult)
  ;; execute in *scratch* buffer, insert the dependent files in buffer
  (progn
    (insert "/n")
    (dolist (file (search-dependent-files 'consult))
      (insert (format "%s\n" file))))

Lazy Load

To Lazy load a package, we have many ways to do it.

Load by special files

For the programming packages, such as eglot, we can load eglot by prog-mode-hook

  (use-package eglot
    :defer t
    :ensure nil  ;; Emacs29+ built-in
    :hook (prog-mode . eglot-ensure) ;; when `prog-mode-hook' executed call `eglot-ensure'
    ...)

Use `auto-mode-alist'

By adding pairs to auto-mode-alist we can enable specified mode when open corresponding files automatically.

  (add-to-list 'auto-mode-alist
               '("\\.ya?ml\\'" . yaml-ts-mode))

Load by Binding or Command

For the tool packages, such as ivy/consult, we can defer them and use bind/commands (from use-package) to load when we first call/use them.

  (use-package consult
    :defer t
    :bind
    ("YOUR BIND" . consult-xxx)
    ...)

Org

I found many org packages loaded in the startup phase. Some of them are not in my configuration directly, and when I use search-dependent-files it returns nil or a list of packages, which is also not in my config files.

So I go to the packages directory, and use rg to search the package name in it.

$ rg --no-ignore 'PACKAGE'
$ rg --no-ignore '(require \'PACKAGE)' ;; the command's result will be more precisely

Finally, I found the emacs-dashboard package load org packages and other packages when I use its widgets. I chose to disable some of them.

  (use-package dashboard
    ...
    :custom
    (dashboard-items '((recents . 10)
                       (projects . 10)))
    ...)

Handle Org Babel Packages

I Learn how to lazy org-babel's packages in 降低 Emacs 启动时间的高级技术. But his code can't use in my Emacs. Here is my config

  (defconst my/org-source-dir (file-name-directory (locate-library "org"))
    "Emacs Built-In ORG-MODE dir.")

  (use-package ob-python
      :defer t
      :ensure nil ;; no need :ensure org-plus-contrib
      :load-path my/org-source-dir
      ;; use :commands to load
      :commands (org-babel-execute:python
                 org-babel-expand-body:python))