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author | Jonathan Corbet <corbet@lwn.net> | 2018-08-02 21:40:57 +0300 |
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committer | Jonathan Corbet <corbet@lwn.net> | 2018-08-02 21:40:57 +0300 |
commit | 0bf1bd84f3657dc51acb9d30629c1967a6b91e76 (patch) | |
tree | c28f81c72fd5421297df0895bfc4fc2c941025ad /Documentation | |
parent | d1634e1aedbc7c30fbba819f8f4fb37df076f49c (diff) | |
parent | ae9d88454446a314f9cda785a072a0c77a81591b (diff) | |
download | linux-0bf1bd84f3657dc51acb9d30629c1967a6b91e76.tar.xz |
Merge branch 'rppt' into docs-next
This contains a set of early-boot memory-management docs from Mike
Rapoport. It's been circulating on linux-mm for a long time; I finally
picked it up even though it changes a lot of .c files under mm/ (comments
only).
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/core-api/boot-time-mm.rst | 92 | ||||
-rw-r--r-- | Documentation/core-api/index.rst | 1 |
2 files changed, 93 insertions, 0 deletions
diff --git a/Documentation/core-api/boot-time-mm.rst b/Documentation/core-api/boot-time-mm.rst new file mode 100644 index 000000000000..03cb1643f46f --- /dev/null +++ b/Documentation/core-api/boot-time-mm.rst @@ -0,0 +1,92 @@ +=========================== +Boot time memory management +=========================== + +Early system initialization cannot use "normal" memory management +simply because it is not set up yet. But there is still need to +allocate memory for various data structures, for instance for the +physical page allocator. To address this, a specialized allocator +called the :ref:`Boot Memory Allocator <bootmem>`, or bootmem, was +introduced. Several years later PowerPC developers added a "Logical +Memory Blocks" allocator, which was later adopted by other +architectures and renamed to :ref:`memblock <memblock>`. There is also +a compatibility layer called `nobootmem` that translates bootmem +allocation interfaces to memblock calls. + +The selection of the early allocator is done using +``CONFIG_NO_BOOTMEM`` and ``CONFIG_HAVE_MEMBLOCK`` kernel +configuration options. These options are enabled or disabled +statically by the architectures' Kconfig files. + +* Architectures that rely only on bootmem select + ``CONFIG_NO_BOOTMEM=n && CONFIG_HAVE_MEMBLOCK=n``. +* The users of memblock with the nobootmem compatibility layer set + ``CONFIG_NO_BOOTMEM=y && CONFIG_HAVE_MEMBLOCK=y``. +* And for those that use both memblock and bootmem the configuration + includes ``CONFIG_NO_BOOTMEM=n && CONFIG_HAVE_MEMBLOCK=y``. + +Whichever allocator is used, it is the responsibility of the +architecture specific initialization to set it up in +:c:func:`setup_arch` and tear it down in :c:func:`mem_init` functions. + +Once the early memory management is available it offers a variety of +functions and macros for memory allocations. The allocation request +may be directed to the first (and probably the only) node or to a +particular node in a NUMA system. There are API variants that panic +when an allocation fails and those that don't. And more recent and +advanced memblock even allows controlling its own behaviour. + +.. _bootmem: + +Bootmem +======= + +(mostly stolen from Mel Gorman's "Understanding the Linux Virtual +Memory Manager" `book`_) + +.. _book: https://www.kernel.org/doc/gorman/ + +.. kernel-doc:: mm/bootmem.c + :doc: bootmem overview + +.. _memblock: + +Memblock +======== + +.. kernel-doc:: mm/memblock.c + :doc: memblock overview + + +Functions and structures +======================== + +Common API +---------- + +The functions that are described in this section are available +regardless of what early memory manager is enabled. + +.. kernel-doc:: mm/nobootmem.c + +Bootmem specific API +-------------------- + +These interfaces available only with bootmem, i.e when ``CONFIG_NO_BOOTMEM=n`` + +.. kernel-doc:: include/linux/bootmem.h +.. kernel-doc:: mm/bootmem.c + :nodocs: + +Memblock specific API +--------------------- + +Here is the description of memblock data structures, functions and +macros. Some of them are actually internal, but since they are +documented it would be silly to omit them. Besides, reading the +descriptions for the internal functions can help to understand what +really happens under the hood. + +.. kernel-doc:: include/linux/memblock.h +.. kernel-doc:: mm/memblock.c + :nodocs: diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst index 989c97cc232a..b5379fb740a5 100644 --- a/Documentation/core-api/index.rst +++ b/Documentation/core-api/index.rst @@ -29,6 +29,7 @@ Core utilities circular-buffers gfp_mask-from-fs-io timekeeping + boot-time-mm Interfaces for kernel debugging =============================== |