Randy Dunlap <rdunlap@xxxxxxxxxxxxx> writes: > On 10/8/18 3:03 AM, Punit Agrawal wrote: >> 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. >> >> Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx> >> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> >> Cc: Will Deacon <will.deacon@xxxxxxx> >> Cc: Jonathan Corbet <corbet@xxxxxxx> > > Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Thanks! Catalin, Will - I assume you'll pick this up at some point? Or do arm64 documentation patches get routed by another tree? > > Thanks. > >> --- >> Hi, >> >> This version incorporates the feedback on v1. >> >> Thanks, >> Punit >> >> Documentation/arm64/hugetlbpage.txt | 38 +++++++++++++++++++++++++++++ >> 1 file changed, 38 insertions(+) >> create mode 100644 Documentation/arm64/hugetlbpage.txt >> >> diff --git a/Documentation/arm64/hugetlbpage.txt b/Documentation/arm64/hugetlbpage.txt >> new file mode 100644 >> index 000000000000..cfae87dc653b >> --- /dev/null >> +++ b/Documentation/arm64/hugetlbpage.txt >> @@ -0,0 +1,38 @@ >> +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 >>
