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https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html
Memory Allocation Guide¶. Linux provides a variety of APIs for memory allocation. You can allocate small chunks using kmalloc or kmem_cache_alloc families, large virtually contiguous areas using vmalloc and its derivatives, or you can directly request pages from the page allocator with alloc_pages.It is also possible to use more specialized allocators, for instance cma_alloc or zs_malloc.
https://www.kernel.org/doc/html/latest/core-api/mm-api.html
Memory Allocation Controls¶ Functions which need to allocate memory often use GFP flags to express how that memory should be allocated. The GFP acronym stands for “get free pages”, the underlying memory allocation function. Not every GFP flag is allowed to every function which may allocate memory. Most users will want to use a plain GFP ...
https://www.linuxjournal.com/article/6930
Dec 01, 2003 · Zone modifiers, on the other hand, tell the kernel from where the request should be satisfied. For example, some requests may need to be satisfied from memory that hardware can access through direct memory access (DMA). Finally, type flags specify a type of allocation. They group together relevant action and zone modifiers into a single mnemonic.
https://stackoverflow.com/questions/52785670/dma-on-fpga-cannot-access-kernel-memory-allocated-with-gfp-kernel-flag
The driver initially allocates 4M kernel memory by using the dma_alloc_coherent() with GFP_KERNEL flag. This allocation is inside the range of the CMA. Then from my user space application I call mmap with READ_PROT/WRITE_PROT and MAP_SHARED/MAP_LOCKED flags to map the previously allocated CMA memory and load the image data in there.
https://elinux.org/images/2/23/LinuxCMA-cewg43.pdf
Linux Contiguous Memory Allocator (and a little IOMMU) ... CMA support introduced in Linux kernel v3.5-rc1 ... CMA and IOMMU allow for dynamically allocating DMA memory Support added in v3.5, v3.6 –Backported to LTSI v3.4 Usable by kernel drivers via DMA mapping API
https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/allocating-system-space-memory
Allocating System-Space Memory. 06/16/2017; 2 minutes to read; In this article. Drivers can use system-allocated space within their device extensions as global storage areas for device-specific information. Drivers can use only the kernel stack to pass small amounts of data to their internal routines.
https://forums.xilinx.com/t5/Embedded-Linux/Allocating-large-buffers-from-reserved-memory/td-p/809390
Nov 17, 2017 · Allocating large buffers from reserved memory ... followed the Linux Reserved Memory wiki and was running into similar trouble when trying to allocate large buffers for DMA. Except that memory allocation for me was failing during the of_reserved_mem_init() call in my device driver, even though the shared-dma-pool was successfully created ...
https://forums.xilinx.com/xlnx/attachments/xlnx/ELINUX/10658/1/drivers-session4-dma-4public.pdf
Memory Allocation For DMA – Part 2 The dma_alloc_coherent() function allocates non-cached physically contiguous memory –The name coherent can be a confusing name (for me anyway) –The CPU and the I/O device see the same memory contents without any cache operations –Accesses to the memory by the CPU are the same as a cache miss when the cache is used
https://community.oracle.com/thread/1953413
Mar 29, 2002 · r u sure that u can do in this way because devmap_umem_setup which is called in devmap entry point for mapping kernel memory to user space required a parameter typed ddi_umem_cookie_t. this ddi_umem_cookie_t can obtain by ddi_umem_alloc but how can we get this through DMA allocation.
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