On Sat 30-06-18 17:55:06, 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 <rppt@xxxxxxxxxxxxxxxxxx> Yes this looks reasonable. I would just mention the available debugging options and CONFIG_ARCH_DISCARD_MEMBLOCK. Other than that looks goot to get a rough idea. Improvements can be done on top of course. Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > 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 > +``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 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 > =============================== > -- > 2.7.4 -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
