HugeTLBpage on ARM64¶
Hugepage relies on making efficient use of TLBs to improve performance of address translations. The benefit depends on both -
- the size of hugepages
- size of entries supported by the TLBs
The ARM64 port supports two flavours of hugepages.
1) Block mappings at the pud/pmd level¶
These are regular hugepages where a pmd or a pud page table entry points to a block of memory. Regardless of the supported size of entries in TLB, block mappings reduce the depth of page table walk needed to translate hugepage addresses.
2) Using the Contiguous bit¶
The architecture provides a contiguous bit in the translation table entries (D4.5.3, ARM DDI 0487C.a) that hints to the MMU to indicate that it is one of a contiguous set of entries that can be cached in a single TLB entry.
The contiguous bit is used in Linux to increase the mapping size at the pmd and pte (last) level. The number of supported contiguous entries varies by page size and level of the page table.
The following hugepage sizes are supported -
CONT PTE PMD CONT PMD PUD 4K: 64K 2M 32M 1G 16K: 2M 32M 1G 64K: 2M 512M 16G