Rails admin panel loading slow

I am currently working on rails project with Mongoid ORM. I am using Rails admin gem for data handling at server side. Rails version is 4.1.7, Ruby is 2.1.5. Problem is it takes lot of time to load when admin panel is loaded the first time.

I checked the logs of rails. It appears to query each and every user from "user" table and certainly time taken to load the panel is proportional to number of entries in the user table.

Please help me in speeding the loading of panel. If any other information is required, please ask. Thanks.

Following is the snapshot of rails log.

 MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('5656bd857261693fb10a0000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 10.0400ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('56ae41fe72616930bf030000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 0.4920ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('567d01277261695b8a000000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 5.1850ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('568cad1a7261691ff2030000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 0.5010ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('561144df726169602d000000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 2.4130ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('56ae487e72616930bf460000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 0.4500ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('567d01277261695b8a000000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 5.1940ms
  MOPED: 127.0.0.1:27017 QUERY        database=yeloapp_development collection=users selector={"$query"=>{"_id"=>BSON::ObjectId('56aa51f972616944d1300000')}, "$orderby"=>{:_id=>1}} flags=[] limit=-1 skip=0 batch_size=nil fields
=nil runtime: 6.2580ms

Ability.rb

class Ability
  include CanCan::Ability

  def initialize(user)
    # Define abilities for the passed in user here. For example:
    #
    #   user ||= User.new # guest user (not logged in)
    #   if user.admin?
    #     can :manage, :all
    #   else
    #     can :read, :all
    #   end
    #
    # The first argument to `can` is the action you are giving the user
    # permission to do.
    # If you pass :manage it will apply to every action. Other common actions
    # here are :read, :create, :update and :destroy.
    #
    # The second argument is the resource the user can perform the action on.
    # If you pass :all it will apply to every resource. Otherwise pass a Ruby
    # class of the resource.
    #
    # The third argument is an optional hash of conditions to further filter the
    # objects.
    # For example, here the user can only update published articles.
    #
    #   can :update, Article, :published => true
    #
    # See the wiki for details:
    # https://github.com/CanCanCommunity/cancancan/wiki/Defining-Abilities
    if user &&  user.admin_type == 1
      can :access, :rails_admin       # only allow admin users to access Rails Admin
      can :dashboard  
      can :manage, :all
    end
    if user && user.is_admin? 
      can :access, :rails_admin       # only allow admin users to access Rails Admin
      can :dashboard  
      can :read, :all
      can :manage, :statistic
    end
  end
end

rails_admin.rb

RailsAdmin.config do |config|

  ### Popular gems integration
  ## == Devise ==
  config.authenticate_with do
    warden.authenticate! scope: :user
  end
  config.current_user_method(&:current_user)

  ## == Cancan ==
  #config.authorize_with :cancan

  ## == PaperTrail ==
  # config.audit_with :paper_trail, 'User', 'PaperTrail::Version' # PaperTrail >= 3.0.0

  ### More at https://github.com/sferik/rails_admin/wiki/Base-configuration

  config.actions do
    dashboard                     # mandatory
    index                         # mandatory
    new
    export
    bulk_delete
    show
    edit
    delete
    show_in_app

    ## With an audit adapter, you can add:
    # history_index
    # history_show
  end
end

Edit: I solved the problem (see the answer). But still I would like to know the reason why was it loading so slow. Help is appreciated.

So I solved this problem by explicitly whitelisting the models I wanted to show. So I changed the rails_admin.rb file.

rails_admin.rb

RailsAdmin.config do |config|

  ### Popular gems integration
  ## == Devise ==
  config.authenticate_with do
    warden.authenticate! scope: :user
  end
  config.current_user_method(&:current_user)

  # this is the way to whitelist the models
  config.included_models = [write the name of models you want to show at rails panel]


  ## == Cancan ==
  config.authorize_with :cancan

  ## == PaperTrail ==
  # config.audit_with :paper_trail, 'User', 'PaperTrail::Version' # PaperTrail >= 3.0.0

  ### More at https://github.com/sferik/rails_admin/wiki/Base-configuration

  config.actions do
    dashboard                     # mandatory
    index                         # mandatory
    new
    export
    bulk_delete
    show
    edit
    delete
    show_in_app

    ## With an audit adapter, you can add:
    # history_index
    # history_show
  end
end

Hope it helps someone else.