From Android 15, the pKVM hypervisor supports Transparent Hugepages. This is a Linux feature which allows the kernel to allocate, when possible, a huge-page (typically, 2MiB on a 4K system). This huge-page being the size of a block, the hypervisor can leverage this allocation to also use a block mapping in the stage-2 page tables, instead of 512 individual contiguous single page mappings.
Using block mappings brings a significant performance improvement by reducing the number of stage-2 page faults as well as the TLB pressure. However, finding a huge-page can be difficult on a system where the memory is fragmented.
By default, huge-pages are disabled.
The sysfs configuration file that will enable THP for AVF is
/sys/kernel/mm/transparent_hugepages/shmem_enabled
This always defaults to never. It is recommended to set it to advise to
benefit from the THP performance improvement.
THPs can have an impact on the system depending on the chosen policy. The policy is configured with the following sysfs file:
/sys/kernel/mm/transparent_hugepages/defrag
The recommended policy is never as this has zero impact on the system. THPs
would be used only if some are available.
More information can be found in the Linux admin guide.
The guest VM configuration can select huge-pages with the vm_config.json
option "hugepages": true.
Alternatively, the vm command can also pass --hugepages.