[geofft]

See section 11 "Memory Pressure" of https://www.kernel.org/doc/Documentation/cgroup-v1/memory.tx... - there's a way to get notified via eventfd() if your current cgroup's memory gets low. I believe you can just do this on the root memory cgroup (/sys/fs/cgroup/memory/memory.pressure_level) if you're not setting up actual cgroups for your application.

(Signals for asynchronous conditions are an awkward interface because they can interrupt you between any two assembly instructions. You're not able to release memory in the handler itself; you have to set a flag that gets handled by the main loop. So eventfd makes sense here. I'm assuming iOS is doing something similar by queueing an Objective-C method call. Signals make a lot more sense for segfaults and the like, where you're being interrupted at the exact instruction that isn't working and you need to handle it before executing any more instructions.)