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 possible to control the behavior 37by passing options from command line. For example, to include verbose output, 38append the `-v` options when you run the tests: 39 40$ ./main -v 41 42This will print information about which functions are being tested and the 43number of test cases that passed. 44 45For the full list of options from command line, see `./main --help`. 46 47It is also possible to override different configuration parameters to change 48the test functions. For example, to simulate enabled NUMA, use: 49 50$ make NUMA=1 51 52For the full list of build options, see `make help`. 53 54Project structure 55================= 56 57The project has one target, main, which calls a group of checks for basic and 58allocation functions. Tests for each group are defined in dedicated files, as it 59can be seen here: 60 61memblock 62|-- asm ------------------, 63|-- lib |-- implement function and struct stubs 64|-- linux ------------------' 65|-- scripts 66| |-- Makefile.include -- handles `make` parameters 67|-- tests 68| |-- alloc_api.(c|h) -- memblock_alloc tests 69| |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests 70| |-- alloc_nid_api.(c|h) -- memblock_alloc_try_nid tests 71| |-- basic_api.(c|h) -- memblock_add/memblock_reserve/... tests 72| |-- common.(c|h) -- helper functions for resetting memblock; 73|-- main.c --------------. dummy physical memory definition 74|-- Makefile `- test runner 75|-- README 76|-- TODO 77|-- .gitignore 78 79Simulating physical memory 80========================== 81 82Some allocation functions clear the memory in the process, so it is required for 83memblock to track valid memory ranges. To achieve this, the test suite registers 84with memblock memory stored by test_memory struct. It is a small wrapper that 85points to a block of memory allocated via malloc. For each group of allocation 86tests, dummy physical memory is allocated, added to memblock, and then released 87at the end of the test run. The structure of a test runner checking allocation 88functions is as follows: 89 90int memblock_alloc_foo_checks(void) 91{ 92 reset_memblock_attributes(); /* data structure reset */ 93 dummy_physical_memory_init(); /* allocate and register memory */ 94 95 (...allocation checks...) 96 97 dummy_physical_memory_cleanup(); /* free the memory */ 98} 99 100There's no need to explicitly free the dummy memory from memblock via 101memblock_free() call. The entry will be erased by reset_memblock_regions(), 102called at the beginning of each test. 103 104Known issues 105============ 106 1071. Requesting a specific NUMA node via memblock_alloc_node() does not work as 108 intended. Once the fix is in place, tests for this function can be added. 109 1102. Tests for memblock_alloc_low() can't be easily implemented. The function uses 111 ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low 112 memory of the memory_block. 113 114References 115========== 116 1171. Boot time memory management documentation page: 118 https://www.kernel.org/doc/html/latest/core-api/boot-time-mm.html 119