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51da853e37
On powerpc there are two ways for huge pages to be represented in the top level page table, aka PGD (Page Global Directory). If the address space mapped by an individual PGD entry does not correspond to a given huge page size, then the PGD entry points to a non-standard page table, known as a "hugepd" (Huge Page Directory). The hugepd contains some number of huge page PTEs sufficient to map the address space with the given huge page size. On the other hand, if the address space mapped by an individual PGD entry does correspond exactly to a given huge page size, that PGD entry is used to directly encode the huge page PTE in place. In this case the pgd_huge() wrapper indicates to generic code that the PGD entry is actually a huge page PTE. This commit deals with the pgd_huge() case only, it does nothing with respect to the hugepd case. Over time the size of the virtual address space supported on powerpc has increased several times, which means the location at which huge pages can sit in the tree has also changed. There have also been new huge page sizes added, with the introduction of the Radix MMU. On Power9 and later with the Radix MMU, the largest huge page size in any implementation is 1GB. Since the introduction of Radix, 1GB entries have been supported at the PUD level, with both 4K and 64K base page size. Radix has never had a supported huge page size at the PGD level. On Power8 or earlier, which uses the Hash MMU, or Power9 or later with the Hash MMU enabled, the largest huge page size is 16GB. Using the Hash MMU and a base page size of 4K, 16GB has never been a supported huge page size at the PGD level, due to the geometry being incompatible. The two supported huge page sizes (16M & 16GB) both use the hugepd format. Using the Hash MMU and a base page size of 64K, 16GB pages were supported in the past at the PGD level. However in commit |
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.