RecyclerView and GridView in a fragment XML

I am trying to set a RecyclerView and a GridView to take up 70% and 30% of the layout respectively. I am using a fragment for this as well.

With this xml, neither views appear on the screen:

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
                xmlns:tools="http://ift.tt/LrGmb4"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:paddingLeft="@dimen/activity_horizontal_margin"
                android:paddingRight="@dimen/activity_horizontal_margin"
                android:paddingTop="@dimen/activity_vertical_margin"
                android:paddingBottom="@dimen/activity_vertical_margin"
                android:elevation="5dp"
                tools:context="shamak.self.eventplanner.activities.Activity_NewEvent$PlaceholderFragment">

    <TextView
        android:id="@+id/section_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:weightSum="1">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/list"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="0.7"
            tools:context=".Fragment_i"
            />

        <GridView
            android:id="@+id/grid_view"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="0.3"
            android:numColumns="2"
            android:verticalSpacing="5dp"
            android:horizontalSpacing="5dp"
            >

            </GridView>

    </LinearLayout>

</RelativeLayout>

With the layout_height of the RecyclerView set to match_parent instead, the RecyclerView populates the entire screen:

  <android.support.v7.widget.RecyclerView
            android:id="@+id/list"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            tools:context=".Fragment_i"
            />