Large Page Support

If you allocate large amounts of contiguous memory it may beneficial to use larger pages to consume fewer page table entries and reduce pressure on the TLB. For example a page size of 2 MiB uses 500 times fewer page table entries than the default page size of 4 KiB.

Large pages differ by operating system but is usually supported through mmap.

Linux

Linux supports large pages through HugeTLB Pages

int size = 2 * 1024 * 1024;
int flags = MmapFlags.MAP_SHARED | MmapFlags.MAP_ANONYMOUS | MmapFlags.MAP_HUGETLB | MmapFlags.MAP_HUGE_2MB;
ByteBuffer buffer = Mman.mmap(size, flags);

try {
  // use buffer
} finally {
  Mman.munmap(buffer);
}

Setting up a large page pool is a bit more involved.

Setting up Permissions

First you need to create a group for shared memory usage. Here we call it hugetlb_shm.

groupadd hugetlb_shm
adduser $USER hugetlb_shm
hugeadm --set-shm-group=hugetlb_shm

use

getent group hugetlb_shm

to get the gid. Then configure the gid under vm.hugetlb_shm_group in /etc/sysctl.conf, here our gid is 1001.

vm.hugetlb_shm_group = 1001

Setting up Pools

# minimum of 8 2MB pages with a total size of 16MB
hugeadm --pool-pages-min=2M:8

# maximum of 1024 2MB pages with a total size of 2GB
hugeadm --pool-pages-max=2M:1024

See also

• Huge pages part 2: Interfaces
• Huge pages part 3: Administration
• Hugepages und the Debian Wiki
• hugeadm(8) - Linux man page

macOS

macOS calls their large pages "superpages", it should work out of the box.

int size = 2 * 1024 * 1024;
int flags = MmapFlagsMacOs.MAP_SHARED | MmapFlagsMacOs.MAP_ANONYMOUS | MmapFlagsMacOs.VM_FLAGS_SUPERPAGE_SIZE_2MB;
ByteBuffer buffer = Mman.mmap(size, flags);

try {
  // use buffer
} finally {
  Mman.munmap(buffer);
}