8.3.3. Huge Pages and Transparent Huge Pages (THP)

x86 CPUs usually address memory in 4kB pages, but they are capable of using larger 2 MB or 1 GB pages known as huge pages. KVM guests can be deployed with huge page memory support in order to improve performance by increasing CPU cache hits against the Transaction Lookaside Buffer (TLB).

A kernel feature enabled by default in Red Hat Enterprise Linux 6, huge pages can significantly increase performance, particularly for large memory and memory-intensive workloads. Red Hat Enterprise Linux 6 is able to more effectively manage large amounts of memory by increasing the page size through the use of huge pages.

Red Hat Enterprise Linux 6.7 systems support both 2 MB and 1 GB huge pages, which can be allocated at boot or at runtime. See Section 8.3.3.3, “Enabling 1 GB huge pages for guests at boot or runtime” for instructions on enabling multiple huge page sizes.

cat /sys/kernel/mm/transparent_hugepage/enabled

# cat /sys/kernel/mm/transparent_hugepage/enabled

echo always > /sys/kernel/mm/transparent_hugepage/enabled

# echo always > /sys/kernel/mm/transparent_hugepage/enabled

echo never > /sys/kernel/mm/transparent_hugepage/enabled

# echo never > /sys/kernel/mm/transparent_hugepage/enabled