Single Process Maximum Possible Memory in x64 Linux

Question

is there any memory limit for a single process in x64 Linux?

we are running a Linux Server with 32Gb of RAM and I\'m wondering if I can allocate most of it for a sin

Answer 1

The resource limits are set using setrlimit syscall. You can change them with a shell builtin (e.g. ulimit on bash, limit with zsh).

The practical limit is also related to RAM size and swap size. The free command show these. (Some systems are overcommitting memory, but that is risky).

A process actually don't use RAM, it consumes virtual memory using system calls like mmap (which may get called by malloc). You could even map a portion of a file into memory with that call.

To learn about the memory map of a process 1234, look into the  /proc/1234/maps file. From your own application, read the /proc/self/maps. And you have also /proc/1234/smaps and /proc/self/smaps. Try the command cat /proc/self/mapsto understand the memory map of the process running that cat.

On a 32Gb RAM machine, you can usually run a process with 31 Gb of process space (assuming no other big process exist). If you had also 64Gb of swap, you could run a process of at least 64Gb but that would be unbelievably slow (most of the time would be spent on swapping to disk). You can add swap space (e.g. by swapping to a file, initialized with dd then mkswap, and activated with swapon).

If coding a server, be very careful about memory leaks. The valgrind tool is helpful to hunt such bugs. And you could consider using Boehm's garbage collector