Just thought I would let everyone on the list know that mlock-ing the audio ring buffers used in my render-callbacks has eliminated all HAL overloads and audio drop outs in my application. It's very solid now... I no longer live in fear of a studer or skip. The only exception is when I plug/unplug power from a laptop. This always causes a HAL overload, due I would expect to the processor changing speeds to save power. I know Apple's VM engine is supposed to be able to "learn" memory usage trends in an application, but my theory is that the VM engine has no way of knowing or expecting a sequential read through a ring buffer to get ready (page in) blocks of memory back at the beginning of the buffer as the read approaches the end. Just a guess. mlock works regardless of the cause of the VM glitches.