*scratch*.el

(setq my-helm-source-file-buffers-list
      (helm-make-source "Files" 'my-helm-source-file-buffers-class)
      my-helm-source-nonfile-buffers-list
      (helm-make-source "Buffers" 'my-helm-source-nonfile-buffers-class))
      
(setq helm-mini-default-sources '(my-helm-source-file-buffers-list 
                                  my-helm-source-nonfile-buffers-list
                                  helm-source-recentf
                                  helm-source-buffer-not-found))

helm-buffers-list-cache

(defclass my-helm-source-file-buffers-class (helm-source-sync helm-type-buffer)
  ((buffer-list
    :initarg :buffer-list
    :initform #'helm-buffer-list
    :custom function
    :documentation
    "  A function with no arguments to create buffer list.")
   (init :initform 'helm-buffers-list--init)
   (candidates :initform
               (lambda ()
                 (mapcar 'buffer-name (remove-if-not #'buffer-file-name (buffer-list)))))
   (matchplugin :initform nil)
   (match :initform 'helm-buffers-match-function)
   (persistent-action :initform 'helm-buffers-list-persistent-action)
   (resume :initform (lambda ()
                       (run-with-idle-timer
                        0.1 nil (lambda ()
                                  (with-helm-buffer
                                    (helm-force-update))))))
   (keymap :initform helm-buffer-map)
   (volatile :initform t)
   (mode-line :initform helm-buffer-mode-line-string)
   (persistent-help
    :initform
    "Show this buffer / C-u \\[helm-execute-persistent-action]: Kill this buffer")))

(defclass my-helm-source-nonfile-buffers-class (helm-source-sync helm-type-buffer)
  ((buffer-list
    :initarg :buffer-list
    :initform #'helm-buffer-list
    :custom function
    :documentation
    "  A function with no arguments to create buffer list.")
   (init :initform 'helm-buffers-list--init)
   (candidates :initform
               (lambda ()
                 (mapcar 'buffer-name (remove-if #'buffer-file-name (buffer-list)))))
   (matchplugin :initform nil)
   (match :initform 'helm-buffers-match-function)
   (persistent-action :initform 'helm-buffers-list-persistent-action)
   (resume :initform (lambda ()
                       (run-with-idle-timer
                        0.1 nil (lambda ()
                                  (with-helm-buffer
                                    (helm-force-update))))))
   (keymap :initform helm-buffer-map)
   (volatile :initform t)
   (mode-line :initform helm-buffer-mode-line-string)
   (persistent-help
    :initform
    "Show this buffer / C-u \\[helm-execute-persistent-action]: Kill this buffer")))