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Linux kernel mirror (for testing)
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1HugeTLBpage on ARM64
2====================
3
4Hugepage relies on making efficient use of TLBs to improve performance of
5address translations. The benefit depends on both -
6
7 - the size of hugepages
8 - size of entries supported by the TLBs
9
10The ARM64 port supports two flavours of hugepages.
11
121) Block mappings at the pud/pmd level
13--------------------------------------
14
15These are regular hugepages where a pmd or a pud page table entry points to a
16block of memory. Regardless of the supported size of entries in TLB, block
17mappings reduce the depth of page table walk needed to translate hugepage
18addresses.
19
202) Using the Contiguous bit
21---------------------------
22
23The architecture provides a contiguous bit in the translation table entries
24(D4.5.3, ARM DDI 0487C.a) that hints to the MMU to indicate that it is one of a
25contiguous set of entries that can be cached in a single TLB entry.
26
27The contiguous bit is used in Linux to increase the mapping size at the pmd and
28pte (last) level. The number of supported contiguous entries varies by page size
29and level of the page table.
30
31
32The following hugepage sizes are supported -
33
34 CONT PTE PMD CONT PMD PUD
35 -------- --- -------- ---
36 4K: 64K 2M 32M 1G
37 16K: 2M 32M 1G
38 64K: 2M 512M 16G