Android Oriented Embedded Linux Memory Optimization Technology Research

ION is a common memory manager in the Android system.It provides a unified memory allocation interface for multimedia applications,to solve the memory management interface inconsistencies in the different Android devices.IOMMU is the product of the development of virtualization technology,which is used to support the physical memory virtualization,and it is widely used in the chip company's products.This paper analyzes the basic principles of ION memory manager and proposes a plan of the IOMMU function is used to optimize the ION memory manager to make the Android system more efficient use of physical memory.This thesis also analyzes and optimizes the anonymous memory reclamation method LMK of Android system.In the case of low memory conditions,anonymous memory can be rapidly reclamed.The main work of this paper is as follows.In terms of ION memory manager optimization,IOMMU function interface is added to the original ION framework.It extends the functionality of the ION memory allocator.Then the software adaptation layer between ION module and IOMMU module is implemented.The function of the adaptation layer is to manage the IOVA address space and to call the IOMMU driver interface to implement the mapping of the physical address to IOVA or to release the existing mapping.In term of the driver of IOMMU,the IOMMU three-level page table is completed the creation,release and other operations dynamicly.Page table creation is done incrementally.And page table entries are allocated as needed which saving the memory space that the page table itself consumes.In term of LMK memory reclamation mechanism optimization,through the improvements of LMK target process selection algorithm to achieve the algorithm of reclaiming multiple processes one time.In order to test the work of this paper,some test cases were designed.Taking the process of displaying pictures as an example,the test case of ION memory manager optimization scheme is designed and implemented.The test case allocates physical memory through ION and simultaneously maps physical memory to user space and IOVA space.The picture data is written from the user space,the display device reads the data from the IOVA space and displays successfully.In terms of the testing of the LMK optimization algorithm,taking the simultaneous reclaimation of three processes as an example,the memory allocation time before and after optimization is tested and compared.Memory allocation efficiency improved significantly.