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Documentation/arm64: HugeTLB page implementation

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Arm v8 architecture supports multiple page sizes - 4k, 16k and
64k. Based on the active page size, the Linux port supports
corresponding hugepage sizes at PMD and PUD(4k only) levels.

In addition, the architecture also supports caching larger sized
ranges (composed of multiple entries) at the PTE and PMD level in the
TLBs using the contiguous bit. The Linux port makes use of this
architectural support to enable additional hugepage sizes.

Describe the two different types of hugepages supported by the arm64
kernel and the hugepage sizes enabled by each.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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Punit Agrawal 2018-10-08 11:03:55 +01:00 committed by Catalin Marinas
parent 26a6f87ef5
commit 0c09d48564
1 changed files with 38 additions and 0 deletions
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Documentation/arm64/hugetlbpage.txt Normal file
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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