code: public void setOffscreenPageLimit(int limit) {
          if (limit < DEFAULT_OFFSCREEN_PAGES) {
              Log.w(TAG, "Requested offscreen page limit " + limit + " too small; defaulting to " +
                      DEFAULT_OFFSCREEN_PAGES);
              limit = DEFAULT_OFFSCREEN_PAGES;
          }
          if (limit != mOffscreenPageLimit) {
              mOffscreenPageLimit = limit;
              populate();
          }
      }
docs: Set the number of pages that should be retained to either side of the
  current page in the view hierarchy in an idle state. Pages beyond this
  limit will be recreated from the adapter when needed.
  
  <p>This is offered as an optimization. If you know in advance the number
  of pages you will need to support or have lazy-loading mechanisms in place
  on your pages, tweaking this setting can have benefits in perceived smoothness
  of paging animations and interaction. If you have a small number of pages (3-4)
  that you can keep active all at once, less time will be spent in layout for
  newly created view subtrees as the user pages back and forth.</p>
  
  <p>You should keep this limit low, especially if your pages have complex layouts.
  This setting defaults to 1.</p>
  
  @param limit How many pages will be kept offscreen in an idle state.