> But it has much lesser impact than in, say, Rust, where it's really an allocation (asking kernel for more RAM). Java's Object "allocation" happens in its own heap, which is a big chunk of RAM already pre-allocated from kernel.
What? No. Rust doesn't ask the kernel for each allocation individually. That'd be insane; besides the crushing system call overhead, the kernel only does allocations in whole pages (4 KiB on x86-64) so it'd be incredibly wasteful of RAM.
Rust does the same thing as virtually every non-GCed language. It uses a memory allocator [1] that does bookkeeping in userspace and asks the kernel for big chunks via sbrk and/or mmap/munmap. Probably not the whole heap as a single chunk of virtual memory as in Java, but much closer to that than to the other extreme of a separate kernel call for each allocation.
[1] by default, just libc's malloc and free, although you can override this, and many people choose jemalloc or mimalloc instead. My high-level description applies equally well to any of the three.
What? No. Rust doesn't ask the kernel for each allocation individually. That'd be insane; besides the crushing system call overhead, the kernel only does allocations in whole pages (4 KiB on x86-64) so it'd be incredibly wasteful of RAM.
Rust does the same thing as virtually every non-GCed language. It uses a memory allocator [1] that does bookkeeping in userspace and asks the kernel for big chunks via sbrk and/or mmap/munmap. Probably not the whole heap as a single chunk of virtual memory as in Java, but much closer to that than to the other extreme of a separate kernel call for each allocation.
[1] by default, just libc's malloc and free, although you can override this, and many people choose jemalloc or mimalloc instead. My high-level description applies equally well to any of the three.