I noticed in CI that after re-enabling the screenshot tests, we have failures on qemuarm and qemuarm64 . Investigating this led to

a) a 'workaround' in starting qemu with

-device VGA,vgamem_mb=64,edid=on
+device VGA,vgamem_mb=128,edid=on

aka starting with a '128MB' gfx card instead of 64M which worked before.

b) running top on qemuarm64 showed that 'homescreen' uses >400M memory there versus 175M on qemux86-64
qemuarm
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
271 weston 20 0 251916 90912 18756 R 95.8 4.4 1:15.97 agl-compositor
302 weston 20 0 1416828 426796 38428 S 45.8 20.8 1:06.71 homescreen

qemux86-64:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
266 weston 20 0 557708 177972 89332 S 16.3 8.7 1:31.93 homescreen

So that leads to two questions:
1) what are the memory requirements that we set - to be clear, other examples e.g. yocto with a wayland+phosh demo just run fine with the default settings.
2) is the runtime memory usage expected and why is it so higher on arm/arm64 ?