Hello everyone,
The following patchset implement a Contiguous Memory Allocator. Here
is an excerpt from the documentation which describes what it is and
why is it needed:
The Contiguous Memory Allocator (CMA) is a framework, which allows
setting up a machine-specific configuration for physically-contiguous
memory management. Memory for devices is then allocated according
to that configuration.
The main role of the framework is not to allocate memory, but to
parse and manage memory configurations, as well as to act as an
in-between between device drivers and pluggable allocators. It is
thus not tied to any memory allocation method or strategy.
** Why is it needed?
Various devices on embedded systems have no scatter-getter and/or
IO map support and as such require contiguous blocks of memory to
operate. They include devices such as cameras, hardware video
decoders and encoders, etc.
Such devices often require big memory buffers (a full HD frame is,
for instance, more then 2 mega pixels large, i.e. more than 6 MB
of memory), which makes mechanisms such as kmalloc() ineffective.
Some embedded devices impose additional requirements on the
buffers, e.g. they can operate only on buffers allocated in
particular location/memory bank (if system has more than one
memory bank) or buffers aligned to a particular memory boundary.
Development of embedded devices have seen a big rise recently
(especially in the V4L area) and many such drivers include their
own memory allocation code. Most of them use bootmem-based methods.
CMA framework is an attempt to unify contiguous memory allocation
mechanisms and provide a simple API for device drivers, while
staying as customisable and modular as possible.
** Design
The main design goal for the CMA was to provide a customisable and
modular framework, which could be configured to suit the needs of
individual systems. Configuration specifies a list of memory
regions, which then are assigned to devices. Memory regions can
be shared among many device drivers or assigned exclusively to
one. This has been achieved in the following ways:
1. The core of the CMA does not handle allocation of memory and
management of free space. Dedicated allocators are used for
that purpose.
This way, if the provided solution does not match demands
imposed on a given system, one can develop a new algorithm and
easily plug it into the CMA framework.
The presented solution includes an implementation of a best-fit
algorithm.
2. CMA allows a run-time configuration of the memory regions it
will use to allocate chunks of memory from. The set of memory
regions is given on command line so it can be easily changed
without the need for recompiling the kernel.
Each region has it's own size, alignment demand, a start
address (physical address where it should be placed) and an
allocator algorithm assigned to the region.
This means that there can be different algorithms running at
the same time, if different devices on the platform have
distinct memory usage characteristics and different algorithm
match those the best way.
3. When requesting memory, devices have to introduce themselves.
This way CMA knows who the memory is allocated for. This
allows for the system architect to specify which memory regions
each device should use.
3a. Devices can also specify a "kind" of memory they want.
This makes it possible to configure the system in such
a way, that a single device may get memory from different
memory regions, depending on the "kind" of memory it
requested. For example, a video codec driver might want to
allocate some shared buffers from the first memory bank and
the other from the second to get the highest possible
memory throughput.
For more information please refer to the second patch from the
patchset which contains the documentation.
The patches in the patchset include:
Michal Nazarewicz (4):
lib: rbtree: rb_root_init() function added
The rb_root_init() function initialises an RB tree with a single
node placed in the root. This is more convenient then
initialising an empty tree and then adding an element.
mm: cma: Contiguous Memory Allocator added
This patch is the main patchset that implements the CMA framework
including the best-fit allocator. It also adds a documentation.
mm: cma: Test device and application added
This patch adds a misc device that works as a proxy to the CMA
framework and a simple testing application. This lets one test
the whole framework from user space as well as reply an recorded
allocate/free sequence.
arm: Added CMA to Aquila and Goni
This patch adds the CMA platform initialisation code to two ARM
platforms. It serves as an example of how this is achieved.
Documentation/cma.txt | 435 +++++++++++++++++++
Documentation/kernel-parameters.txt | 7 +
arch/arm/Kconfig | 1 +
arch/arm/mach-s5pv210/Kconfig | 1 +
arch/arm/mach-s5pv210/mach-aquila.c | 7 +
arch/arm/mach-s5pv210/mach-goni.c | 7 +
drivers/misc/Kconfig | 8 +
drivers/misc/Makefile | 1 +
drivers/misc/cma-dev.c | 183 ++++++++
include/linux/cma-int.h | 183 ++++++++
include/linux/cma.h | 122 ++++++
include/linux/rbtree.h | 11 +
mm/Kconfig | 41 ++
mm/Makefile | 3 +
mm/cma-allocators.h | 42 ++
mm/cma-best-fit.c | 360 ++++++++++++++++
mm/cma.c | 778 +++++++++++++++++++++++++++++++++++
tools/cma/cma-test.c | 373 +++++++++++++++++
18 files changed, 2563 insertions(+), 0 deletions(-)
create mode 100644 Documentation/cma.txt
create mode 100644 drivers/misc/cma-dev.c
create mode 100644 include/linux/cma-int.h
create mode 100644 include/linux/cma.h
create mode 100644 mm/cma-allocators.h
create mode 100644 mm/cma-best-fit.c
create mode 100644 mm/cma.c
create mode 100644 tools/cma/cma-test.c
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