High memory consumption with Wayland

The PSS memory consumption using Wayland is about 10MB bigger than using X11o n the same Linux machine. We ran several benchmarks analysing the smaps file to benchmark the PSS for the following code:

import QtQuick 2.3
Rectangle {
    id: blub
    height: 640
    width: 480
    color: "red"
}

Run with "qmlscene rec.qml", you get an RSS value of 38M. If you start the application 5 times you get the following PSS values:

#of scenes 1   2  3  4 5
PSS        16 13 11 10 9 (average) 

If you run the same test using "qmlscene -platform wayland rec.qml", you get an RSS of 44M and following PSS values:

#of scenes  1  2  3  4  5
PSS        28 23 21 19 20 (average) 

For an embedded multiprocess system (our actual target) it is way too much.

(This issue relates to support request INC-1153879)