by Randy Dunlap

[permalink] [raw]

Subject: Re: [PATCH 04/11] docs/mm: bootmem: add kernel-doc description of 'struct bootmem_data'

On 06/18/2018 09:59 AM, Mike Rapoport wrote:
> Signed-off-by: Mike Rapoport <[email protected]>
> ---
> include/linux/bootmem.h | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
> index 7942a96..1526ba1 100644
> --- a/include/linux/bootmem.h
> +++ b/include/linux/bootmem.h
> @@ -27,9 +27,20 @@ extern unsigned long max_pfn;
> extern unsigned long long max_possible_pfn;
>
> #ifndef CONFIG_NO_BOOTMEM
> -/*
> - * node_bootmem_map is a map pointer - the bits represent all physical
> - * memory pages (including holes) on the node.
> +/**
> + * struct bootmem_data - per-node information used by the bootmem allocator
> + * @node_min_pfn: the starting physical address of the node's memory
> + * @node_low_pfn: the end physical address of the directly addressable memory
> + * @node_bootmem_map: is a bitmap pointer - the bits represent all physical
> + * memory pages (including holes) on the node.
> + * @last_end_off: the offset within the page of the end of the last allocation;
> + * if 0, the page used is full
> + * @hint_idx: the the PFN of the page used with the last allocation;

drop one "the" above.

> + * together with using this with the @last_end_offset field,
> + * a test can be made to see if allocations can be merged
> + * with the page used for the last allocation rather than
> + * using up a full new page.
> + * @list: list entry in the linked list ordered by the memory addresses
> */
> typedef struct bootmem_data {
> unsigned long node_min_pfn;
>

--
~Randy

2018-06-18 17:34:05

by Randy Dunlap

[permalink] [raw]

Subject: Re: [PATCH 11/11] docs/mm: add description of boot time memory management

On 06/18/2018 09:59 AM, Mike Rapoport wrote:
> 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 <[email protected]>
> ---
> 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..379e5a3
> --- /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" which was later adopted by other architectures and

Memory Blocks" allocator, which was later ...

> +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 alocator is done using

allocator

> +``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

fix ending: =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 manegement is available it offers variety of

management 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
> +--------------------
> +
> +The interfaces available only with bootmem, i.e when ``CONFIG_NO_BOOTMEM=n``

i.e.
How about:

These interfaces are 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
> printk-formats
> circular-buffers
> gfp_mask-from-fs-io
> + boot-time-mm
>
> Interfaces for kernel debugging
> ===============================
>

--
~Randy