Gap in Bootstrap stacked rows

There are a couple of ways to handle this:

1. Give all of the elements in your portfolio a set height.
2. Use something like masonry to dynamically “fit” the elements into the available space.
3. Use the responsive classes and clearfix as described in the doc under the heading Responsive column resets, in the Grid secion.
4. Use jQuery to adjust the column heights dynamically.

If your content is dynamically generated so that you don’t know which elements will have longer content, and you have different layouts set for different breakpoints, the responsive classes approach can be a bear to adapt. I use a little trick. After each element in the grid, I add a div that I can apply a mini clearfix to using media queries. It’s extra markup, but it solves the problem nicely and allows me to have readable and maintainable markup while avoiding the use of javascript to adjust the layout. Here’s an example using your markup:

Updated Bootply

<div class="row portfolio"> <!--Add a class so you can target with nth-child-->
    <div class="col-lg-2 col-sm-3 col-xs-4">
        <div class="panel panel-default">
            <div class="panel-body">
                <a href="#">
                    <img src="http://placehold.it/200x200" class="img-thumbnail img-responsive">
                </a>
            </div>
            <div class="panel-footer">
                This is text
            </div>  
        </div> 
    </div>
    <div class="clear"></div> <!--Here's the added div after every element-->
  ....
</div> <!--/.portfolio.row-->

CSS:

@media (max-width: 767px) {
    .portfolio>.clear:nth-child(6n)::before {
      content: '';
      display: table;
      clear: both;
    }
}
@media (min-width: 768px) and (max-width: 1199px) {
    .portfolio>.clear:nth-child(8n)::before {
      content: '';
      display: table;
      clear: both;
    }
}
@media (min-width: 1200px) {
    .portfolio>.clear:nth-child(12n)::before {  
      content: '';
      display: table;
      clear: both;
    }
}

If you prefer the jQuery route (again, this assumes that you’ve added a class “portfolio” to the row that contains your portfolio elements for easier targeting):

var row=$('.portfolio');
$.each(row, function() {
    var maxh=0;
    $.each($(this).find('div[class^="col-"]'), function() {
        if($(this).height() > maxh)
            maxh=$(this).height();
    });
    $.each($(this).find('div[class^="col-"]'), function() {
        $(this).height(maxh);
    });
});