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