[PATCH 0/4] The Contiguous Memory Allocator
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From: Michal Nazarewicz on 20 Jul 2010 12:00 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |