I tried it again with current mesa git master
(ae95b9dd9be56ad84a8a4ab5955f580c337259cb) together with libdrm git master
(07fead4462b2d537d0c3cae69a09272fc426c598) and I am being spammed with the
following messages before the computer locks up:

localhost kernel: [ 2991.517056] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517169] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517189] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517249] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517271] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517374] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517394] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517438] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517458] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517537] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517558] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517651] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517677] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517778] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517799] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517844] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517863] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517955] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.517976] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518018] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518037] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518153] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518175] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518221] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518253] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518354] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518376] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518420] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518443] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518520] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518541] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518620] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518639] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518718] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518739] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518782] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518801] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518931] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518952] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.518995] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.519013] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.519090] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit
localhost kernel: [ 2991.519109] radeon_gem_object_create:62 alloc size 341Mb
bigger than 256Mb limit