how to make an ionic list scrollable?

Give your <ion-scroll> directive a height attribute: Eg.

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<ion-scroll style="height: 200px">
  <ion-list>
     <ion-item ng-repeat="item in items">{{item}}</ion-item>
  </ion-list>
</ion-scroll>

ion-scroll doesn't exist anymore, div could be use instead

the above css could be actualized like the following

div[scrollx=true],div[scrolly=true] {
     position: relative;
     overflow: hidden;
}

div[scrollx=true] {
    overflow-x: auto;
}

div[scrolly=true] {
    overflow-y: auto;
}

<div scrolly="true" style="max-height:100px">
    <!--content to scroll whose height exceeds 100px-->
</div>