I recently came across the following disconcerting message in my kernel’s boot output:
Truncating RAM at 40000000-5fffffff to -57ffffff (vmalloc region overlap). ... Kernel command line: console=ttySC0,115200 mem=512M ... Memory: 384MB = 384MB total
Which is the kernel’s way of saying “I understand there may be some RAM here – but I’m not going to use it all”. So what is the cause of this warning? And what do we need to do to reclaim that lost RAM?