Hi all :)
I tried to raise this in the group lab and was pointed here.
I’m seeing a flat per-app memory ceiling of about 6 GB on iPhone, even on devices with more physical RAM and with com.apple.developer.kernel.increased-memory-limit.
Measured with os_proc_available_memory() plus task_vm_info.phys_footprint, the total process budget stays around 6144 MB on both:
- iPhone 16 Pro Max, 8 GB RAM
- iPhone 17 Pro Max, 12 GB RAM
This came up while running Gemma 4 multimodal support in mlx-swift-lm (PR #343). The model loads at about 4.4 GB resident, leaving roughly 1.7 GB for inference/prefill. Reducing a GPU buffer cache from 512 MB to 64 MB recovered enough headroom to avoid jetsam and allowed a full image + video + audio multimodal test to complete, so the measurement seems to reflect a real per-process limit rather than free system memory.
I re-measured the ceiling on the 12 GB phone with these capabilities:
increased-memory-limitonly: ~6144 MBincreased-memory-limit+extended-virtual-addressing: ~6144 MB, no changeincreased-memory-limit+increased-debugging-memory-limit: ~6656 MB
I have also observed that 12 GB iPad devices expose more memory to an app than 12 GB iPhone devices but I didn't measure specifically and no longer have the device to hand.
Is the ~6 GB per-process tier on Pro iPhones expected, even with increased-memory-limit?
Is there any supported way for a shipping app to access more of the available RAM on 12 GB iPhone models?
FB23183521