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b250c8c08c
At the time being, 512k huge pages are handled through hugepd page tables. The PMD entry is flagged as a hugepd pointer and it means that only 512k hugepages can be managed in that 4M block. However, the hugepd table has the same size as a normal page table, and 512k entries can therefore be nested with normal pages. On the 8xx, TLB loading is performed by software and allthough the page tables are organised to match the L1 and L2 level defined by the HW, all TLB entries have both L1 and L2 independent entries. It means that even if two TLB entries are associated with the same PMD entry, they can be loaded with different values in L1 part. The L1 entry contains the page size (PS field): - 00 for 4k and 16 pages - 01 for 512k pages - 11 for 8M pages By adding a flag for hugepages in the PTE (_PAGE_HUGE) and copying it into the lower bit of PS, we can then manage 512k pages with normal page tables: - PMD entry has PS=11 for 8M pages - PMD entry has PS=00 for other pages. As a PMD entry covers 4M areas, a PMD will either point to a hugepd table having a single entry to an 8M page, or the PMD will point to a standard page table which will have either entries to 4k or 16k or 512k pages. For 512k pages, as the L1 entry will not know it is a 512k page before the PTE is read, there will be 128 entries in the PTE as if it was 4k pages. But when loading the TLB, it will be flagged as a 512k page. Note that we can't use pmd_ptr() in asm/nohash/32/pgtable.h because it is not defined yet. In ITLB miss, we keep the possibility to opt it out as when kernel text is pinned and no user hugepages are used, we can save several instruction by not using r11. In DTLB miss, that's just one instruction so it's not worth bothering with it. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/002819e8e166bf81d24b24782d98de7c40905d8f.1589866984.git.christophe.leroy@csgroup.eu |
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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.