I'm having serious issues with some R7 270x. It runs 2 threads and each thread allocates a 512MB, 256MB, 128MB and 4KB buffer in global device memory (in total: ~1.8GB). On some 270x I observed that only ~1.3GB are allocated in device memory and ~500MB in host memory (Catalyst 14.6 and Catalyst 14.7 on Windows7 64bit). The performance decreases by a factor ~10 if some memory is allocated in host memory. Using a R9 280x I observed from time to time similar behaviour but a reboot always helped (my R9 290 never showed this). The 270x shows this behaviour permanently on some computers.
Does someone know why not all memory is allocated in device memory?