diff --git a/app/controllers/user_admin_controller.rb b/app/controllers/user_admin_controller.rb
--- a/app/controllers/user_admin_controller.rb
+++ b/app/controllers/user_admin_controller.rb
@@ -39,7 +39,7 @@
       redirect_to :action => 'index'
     else
       render :action => 'new'
-    end    
+    end
   end
 
   def clear_last_ip
@@ -52,92 +52,23 @@
   def create_from_list
     lines = params[:user_list]
 
-    note = []
-    error_note = []
-    error_msg = nil
-    ok_user = []
-
-    lines.split("\n").each do |line|
-      #split with large limit, this will cause consecutive ',' to be result in a blank
-      items = line.chomp.split(',',1000)
-      if items.length>=2
-        login = items[0]
-        full_name = items[1]
-        remark =''
-        user_alias = ''
-
-        added_random_password = false
-        added_password = false
-        if items.length >= 3
-          if items[2].chomp(" ").length > 0
-            password = items[2].chomp(" ")
-            added_password = true
-          end
-        else
-          password = random_password
-          added_random_password=true;
-        end
-
-        if items.length>= 4 and items[3].chomp(" ").length > 0;
-          user_alias = items[3].chomp(" ")
-        else
-          user_alias = login
-        end
-
 
-        has_remark = false
-        if items.length>=5
-          remark = items[4].strip;
-          has_remark = true
-        end
+    res = User.create_from_list(lines)
+    error_logins = res[:error_logins]
+    error_msg = res[:first_error]
+    ok_user = res[:created_users]
 
-        user = User.find_by_login(login)
-        if (user)
-          user.full_name = full_name
-          user.remark = remark if has_remark
-          user.password = password if added_password || added_random_password
-        else
-          #create a random password if none are given
-          password = random_password unless password
-          user = User.new({:login => login,
-                           :full_name => full_name,
-                           :password => password,
-                           :password_confirmation => password,
-                           :alias => user_alias,
-                           :remark => remark})
-        end
-        user.activated = true
-
-        if user.save
-          if added_random_password
-            note << "'#{login}' (+)"
-          else
-            note << login
-          end
-          ok_user << user
-        else
-          error_note << "'#{login}'"
-          error_msg = user.errors.full_messages.to_sentence unless error_msg
-        end
-
-      end
-    end
 
     #add to group
     if params[:add_to_group]
-      group = Group.where(id: params[:group_id]).first
-      if group
-        group.users << ok_user
-      end
+      group = Group.find_by(id: params[:group_id])&.add_users_skip_existing(ok_user)
     end
 
     # show flash
-    if note.size > 0
-      flash[:success] = 'User(s) ' + note.join(', ') + 
-        ' were successfully created.  ' +
-        '( (+) - created with random passwords.)'   
+    if ok_user.count > 0
+      flash[:success] = "#{ok_user.count} user(s) was created or updated successfully"
     end
-    if error_note.size > 0
+    if error_logins.size > 0
       flash[:error] = "Following user(s) failed to be created: " + error_note.join(', ') + ". The error of the first failed one are: " + error_msg;
     end
     redirect_to :action => 'index'
@@ -401,7 +332,7 @@
       flash[:notice] = 'You entered an empty mail subject.'
       redirect_to :action => 'mass_mailing' and return
     end
-    
+
     mail_body = params[:email_body]
     if !mail_body or mail_body.blank?
       flash[:notice] = 'You entered an empty mail body.'
@@ -417,7 +348,7 @@
         note << user.login
       end
     end
-    
+
     flash[:notice] = 'User(s) ' + note.join(', ') + 
       ' were successfully modified.  ' 
     redirect_to :action => 'mass_mailing'
@@ -426,9 +357,14 @@
   #bulk manage
   def bulk_manage
 
-    begin 
-      @users = User.where('(login REGEXP ?) OR (remark REGEXP ?)',params[:regex],params[:regex]) if params[:regex]
-      @users.count if @users #i don't know why I have to call count, but if I won't exception is not raised
+    begin
+      if params[:filter_group]
+        @users = Group.find_by(id: params[:filter_group_id]).users
+      else
+        @users = User.all
+      end
+      @users = @users.where('(login REGEXP ?) OR (remark REGEXP ?)',params[:regex],params[:regex]) unless params[:regex].blank?
+      @users.count if @users #test the sql
     rescue Exception
       flash[:error] = 'Regular Expression is malformed'
       @users = nil
diff --git a/app/models/group.rb b/app/models/group.rb
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -8,6 +8,13 @@
   #has_and_belongs_to_many :problems
   #has_and_belongs_to_many :users
 
+  def add_users_skip_existing(users_list)
+    new_list = []
+    users_list.each do |u|
+      new_list << u unless users.include? u
+    end
+    users << new_list
+  end
 
 end
 
diff --git a/app/models/user.rb b/app/models/user.rb
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -136,10 +136,6 @@
     password
   end
 
-  def self.find_non_admin_with_prefix(prefix='')
-    users = User.all
-    return users.find_all { |u| !(u.admin?) and u.login.index(prefix)==0 }
-  end
 
   # Contest information
 
@@ -314,13 +310,91 @@
     User.update_all(:last_ip => nil)
   end
 
+  #create multiple user, one per lines of input
+  def self.create_from_list(lines)
+    error_logins = []
+    first_error = nil
+    created_users = []
+
+    lines.split("\n").each do |line|
+      #split with large limit, this will cause consecutive ',' to be result in a blank
+      items = line.chomp.split(',',1000)
+      if items.length>=2
+        login = items[0]
+        full_name = items[1]
+        remark =''
+        user_alias = ''
+
+        added_random_password = false
+        added_password = false
+
+        #given password?
+        if items.length >= 3
+          if items[2].chomp(" ").length > 0
+            password = items[2].chomp(" ")
+            added_password = true
+          end
+        else
+          password = random_password
+          added_random_password=true;
+        end
+
+        #given alias?
+        if items.length>= 4 and items[3].chomp(" ").length > 0;
+          user_alias = items[3].chomp(" ")
+        else
+          user_alias = login
+        end
+
+        #given remark?
+        has_remark = false
+        if items.length>=5
+          remark = items[4].strip;
+          has_remark = true
+        end
+
+        user = User.find_by_login(login)
+        if (user)
+          user.full_name = full_name
+          user.remark = remark if has_remark
+          user.password = password if added_password || added_random_password
+        else
+          #create a random password if none are given
+          password = random_password unless password
+          user = User.new({:login => login,
+                           :full_name => full_name,
+                           :password => password,
+                           :password_confirmation => password,
+                           :alias => user_alias,
+                           :remark => remark})
+        end
+        user.activated = true
+
+        if user.save
+          created_users << user
+        else
+          error_logins << "'#{login}'"
+          first_error = user.errors.full_messages.to_sentence unless first_error
+        end
+      end
+    end
+
+    return {error_logins: error_logins, first_error: first_error, created_users: created_users}
+
+  end
+
+  def self.find_non_admin_with_prefix(prefix='')
+    users = User.all
+    return users.find_all { |u| !(u.admin?) and u.login.index(prefix)==0 }
+  end
+
   protected
     def encrypt_new_password
       return if password.blank?
       self.salt = (10+rand(90)).to_s
       self.hashed_password = User.encrypt(self.password,self.salt)
     end
-  
+
     def assign_default_site
       # have to catch error when migrating (because self.site is not available).
       begin
diff --git a/app/views/user_admin/bulk_manage.html.haml b/app/views/user_admin/bulk_manage.html.haml
--- a/app/views/user_admin/bulk_manage.html.haml
+++ b/app/views/user_admin/bulk_manage.html.haml
@@ -23,6 +23,12 @@
           %li
             %code 21$
             matches every user whose login ends with "21"
+        .form-group
+          .div.checkbox
+            %label
+              = check_box_tag :filter_group, 1, params[:filter_group] == '1'
+              Apply to this group only
+            = select_tag "filter_group_id", options_from_collection_for_select( Group.all, 'id','name',params[:filter_group_id]), id: 'group_name',class: 'select2'
   .col-md-6
     .panel.panel-primary
       .panel-title.panel-heading
diff --git a/db/migrate/20210809105935_add_index_to_task_status.rb b/db/migrate/20210809105935_add_index_to_task_status.rb
new file mode 100644
--- /dev/null
+++ b/db/migrate/20210809105935_add_index_to_task_status.rb
@@ -0,0 +1,5 @@
+class AddIndexToTaskStatus < ActiveRecord::Migration[5.2]
+  def change
+    add_index :tasks, :status
+  end
+end