On Linux, most (maybe even all) of the data structures that must grow with memory size can be carved out of the memory being added. The main culprit is 'struct

On Linux, most (maybe even all) of the data structures that must grow with memory size can be carved out of the memory being added. The main culprit is 'struct page' which typically needs 64b of metadata for each 4k physical page (on x86 at least). Much of the code to do this stuff is in Linux's "sparsemem" infrastructure: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/sparse.c https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...