93 lines
3 KiB
ReStructuredText
93 lines
3 KiB
ReStructuredText
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===========================
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Boot time memory management
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===========================
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Early system initialization cannot use "normal" memory management
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simply because it is not set up yet. But there is still need to
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allocate memory for various data structures, for instance for the
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physical page allocator. To address this, a specialized allocator
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called the :ref:`Boot Memory Allocator <bootmem>`, or bootmem, was
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introduced. Several years later PowerPC developers added a "Logical
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Memory Blocks" allocator, which was later adopted by other
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architectures and renamed to :ref:`memblock <memblock>`. There is also
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a compatibility layer called `nobootmem` that translates bootmem
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allocation interfaces to memblock calls.
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The selection of the early allocator is done using
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``CONFIG_NO_BOOTMEM`` and ``CONFIG_HAVE_MEMBLOCK`` kernel
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configuration options. These options are enabled or disabled
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statically by the architectures' Kconfig files.
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* Architectures that rely only on bootmem select
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``CONFIG_NO_BOOTMEM=n && CONFIG_HAVE_MEMBLOCK=n``.
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* The users of memblock with the nobootmem compatibility layer set
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``CONFIG_NO_BOOTMEM=y && CONFIG_HAVE_MEMBLOCK=y``.
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* And for those that use both memblock and bootmem the configuration
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includes ``CONFIG_NO_BOOTMEM=n && CONFIG_HAVE_MEMBLOCK=y``.
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Whichever allocator is used, it is the responsibility of the
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architecture specific initialization to set it up in
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:c:func:`setup_arch` and tear it down in :c:func:`mem_init` functions.
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Once the early memory management is available it offers a variety of
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functions and macros for memory allocations. The allocation request
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may be directed to the first (and probably the only) node or to a
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particular node in a NUMA system. There are API variants that panic
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when an allocation fails and those that don't. And more recent and
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advanced memblock even allows controlling its own behaviour.
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.. _bootmem:
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Bootmem
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=======
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(mostly stolen from Mel Gorman's "Understanding the Linux Virtual
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Memory Manager" `book`_)
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.. _book: https://www.kernel.org/doc/gorman/
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.. kernel-doc:: mm/bootmem.c
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:doc: bootmem overview
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.. _memblock:
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Memblock
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========
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.. kernel-doc:: mm/memblock.c
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:doc: memblock overview
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Functions and structures
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========================
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Common API
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----------
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The functions that are described in this section are available
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regardless of what early memory manager is enabled.
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.. kernel-doc:: mm/nobootmem.c
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Bootmem specific API
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--------------------
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These interfaces available only with bootmem, i.e when ``CONFIG_NO_BOOTMEM=n``
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.. kernel-doc:: include/linux/bootmem.h
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.. kernel-doc:: mm/bootmem.c
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:nodocs:
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Memblock specific API
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---------------------
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Here is the description of memblock data structures, functions and
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macros. Some of them are actually internal, but since they are
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documented it would be silly to omit them. Besides, reading the
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descriptions for the internal functions can help to understand what
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really happens under the hood.
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.. kernel-doc:: include/linux/memblock.h
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.. kernel-doc:: mm/memblock.c
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:nodocs:
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