[SOLVED] mmap error : cannot allocate memory. how to allocate enough default sized huge pages as admin?

Issue

I was compiling and running this program but received 'mmap error : cannot allocate memory'. The comment at the top reads

/*
 * Example of using hugepage memory in a user application using the mmap
 * system call with MAP_HUGETLB flag.  Before running this program make
 * sure the administrator has allocated enough default sized huge pages
 * to cover the 256 MB allocation.
 *
 * For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
 * That means the addresses starting with 0x800000... will need to be
 * specified.  Specifying a fixed address is not required on ppc64, i386
 * or x86_64.
 */

I want to check if the administrator has allocated enough default sized huge pages to cover the 256 MB allocation but I am the system administrator. What should I do? I'm on ubuntu 20.04 x86_64 machine. ( a side question : Does mmap use heap area?)

ADD : please see my comment (I added a boot command argument and the code works. I temporarily added boot argument in the grub menu.) but I wish I could add a init script so that this takes effect every time the computer boots.

Solution

There seem to be 2 methods.

1. add vm.nr_hugepages = 16 in /etc/sysctrl.conf and reboot.
   I've checked this works.

2. (as Nate Eldredge commented) add 'hugepages=16' in GRUB_CMDLINE_LINUX="" line (inside quotes) of /etc/default/grub and do update-grub.

Answered By - Chan Kim