README (4185B)
1================== 2Memblock simulator 3================== 4 5Introduction 6============ 7 8Memblock is a boot time memory allocator[1] that manages memory regions before 9the actual memory management is initialized. Its APIs allow to register physical 10memory regions, mark them as available or reserved, allocate a block of memory 11within the requested range and/or in specific NUMA node, and many more. 12 13Because it is used so early in the booting process, testing and debugging it is 14difficult. This test suite, usually referred as memblock simulator, is 15an attempt at testing the memblock mechanism. It runs one monolithic test that 16consist of a series of checks that exercise both the basic operations and 17allocation functionalities of memblock. The main data structure of the boot time 18memory allocator is initialized at the build time, so the checks here reuse its 19instance throughout the duration of the test. To ensure that tests don't affect 20each other, region arrays are reset in between. 21 22As this project uses the actual memblock code and has to run in user space, 23some of the kernel definitions were stubbed by the initial commit that 24introduced memblock simulator (commit 16802e55dea9 ("memblock tests: Add 25skeleton of the memblock simulator")) and a few preparation commits just 26before it. Most of them don't match the kernel implementation, so one should 27consult them first before making any significant changes to the project. 28 29Usage 30===== 31 32To run the tests, build the main target and run it: 33 34$ make && ./main 35 36A successful run produces no output. It is also possible to override different 37configuration parameters. For example, to simulate enabled NUMA, use: 38 39$ make NUMA=1 40 41For the full list of options, see `make help`. 42 43Project structure 44================= 45 46The project has one target, main, which calls a group of checks for basic and 47allocation functions. Tests for each group are defined in dedicated files, as it 48can be seen here: 49 50memblock 51|-- asm ------------------, 52|-- lib |-- implement function and struct stubs 53|-- linux ------------------' 54|-- scripts 55| |-- Makefile.include -- handles `make` parameters 56|-- tests 57| |-- alloc_api.(c|h) -- memblock_alloc tests 58| |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests 59| |-- alloc_nid_api.(c|h) -- memblock_alloc_try_nid tests 60| |-- basic_api.(c|h) -- memblock_add/memblock_reserve/... tests 61| |-- common.(c|h) -- helper functions for resetting memblock; 62|-- main.c --------------. dummy physical memory definition 63|-- Makefile `- test runner 64|-- README 65|-- TODO 66|-- .gitignore 67 68Simulating physical memory 69========================== 70 71Some allocation functions clear the memory in the process, so it is required for 72memblock to track valid memory ranges. To achieve this, the test suite registers 73with memblock memory stored by test_memory struct. It is a small wrapper that 74points to a block of memory allocated via malloc. For each group of allocation 75tests, dummy physical memory is allocated, added to memblock, and then released 76at the end of the test run. The structure of a test runner checking allocation 77functions is as follows: 78 79int memblock_alloc_foo_checks(void) 80{ 81 reset_memblock_attributes(); /* data structure reset */ 82 dummy_physical_memory_init(); /* allocate and register memory */ 83 84 (...allocation checks...) 85 86 dummy_physical_memory_cleanup(); /* free the memory */ 87} 88 89There's no need to explicitly free the dummy memory from memblock via 90memblock_free() call. The entry will be erased by reset_memblock_regions(), 91called at the beginning of each test. 92 93Known issues 94============ 95 961. Requesting a specific NUMA node via memblock_alloc_node() does not work as 97 intended. Once the fix is in place, tests for this function can be added. 98 992. Tests for memblock_alloc_low() can't be easily implemented. The function uses 100 ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low 101 memory of the memory_block. 102 103References 104========== 105 1061. Boot time memory management documentation page: 107 https://www.kernel.org/doc/html/latest/core-api/boot-time-mm.html