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Subject[PATCH v2 11/11] docs/mm: add description of boot time memory management
Both bootmem and memblock are have pretty good internal documentation
coverage. With addition of some overview we get a nice description of the
early memory management.

Signed-off-by: Mike Rapoport <>
Documentation/core-api/boot-time-mm.rst | 92 +++++++++++++++++++++++++++++++++
Documentation/core-api/index.rst | 1 +
2 files changed, 93 insertions(+)
create mode 100644 Documentation/core-api/boot-time-mm.rst

diff --git a/Documentation/core-api/boot-time-mm.rst b/Documentation/core-api/boot-time-mm.rst
new file mode 100644
index 0000000..03cb164
--- /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
+configuration options. These options are enabled or disabled
+statically by the architectures' Kconfig files.
+* Architectures that rely only on bootmem select
+* The users of memblock with the nobootmem compatibility layer set
+* And for those that use both memblock and bootmem the configuration
+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:
+(mostly stolen from Mel Gorman's "Understanding the Linux Virtual
+Memory Manager" `book`_)
+.. _book:
+.. kernel-doc:: mm/bootmem.c
+ :doc: bootmem overview
+.. _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 f5a66b7..93d5a46 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -28,6 +28,7 @@ Core utilities
+ boot-time-mm

Interfaces for kernel debugging
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