108 lines
4.1 KiB
Plaintext
108 lines
4.1 KiB
Plaintext
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==================
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Memblock simulator
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==================
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Introduction
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============
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Memblock is a boot time memory allocator[1] that manages memory regions before
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the actual memory management is initialized. Its APIs allow to register physical
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memory regions, mark them as available or reserved, allocate a block of memory
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within the requested range and/or in specific NUMA node, and many more.
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Because it is used so early in the booting process, testing and debugging it is
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difficult. This test suite, usually referred as memblock simulator, is
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an attempt at testing the memblock mechanism. It runs one monolithic test that
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consist of a series of checks that exercise both the basic operations and
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allocation functionalities of memblock. The main data structure of the boot time
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memory allocator is initialized at the build time, so the checks here reuse its
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instance throughout the duration of the test. To ensure that tests don't affect
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each other, region arrays are reset in between.
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As this project uses the actual memblock code and has to run in user space,
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some of the kernel definitions were stubbed by the initial commit that
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introduced memblock simulator (commit 16802e55dea9 ("memblock tests: Add
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skeleton of the memblock simulator")) and a few preparation commits just
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before it. Most of them don't match the kernel implementation, so one should
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consult them first before making any significant changes to the project.
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Usage
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=====
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To run the tests, build the main target and run it:
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$ make && ./main
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A successful run produces no output. It is also possible to override different
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configuration parameters. For example, to simulate enabled NUMA, use:
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$ make NUMA=1
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For the full list of options, see `make help`.
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Project structure
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=================
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The project has one target, main, which calls a group of checks for basic and
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allocation functions. Tests for each group are defined in dedicated files, as it
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can be seen here:
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memblock
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|-- asm ------------------,
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|-- lib |-- implement function and struct stubs
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|-- linux ------------------'
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|-- scripts
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| |-- Makefile.include -- handles `make` parameters
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|-- tests
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| |-- alloc_api.(c|h) -- memblock_alloc tests
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| |-- alloc_helpers_api.(c|h) -- memblock_alloc_from tests
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| |-- alloc_nid_api.(c|h) -- memblock_alloc_try_nid tests
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| |-- basic_api.(c|h) -- memblock_add/memblock_reserve/... tests
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| |-- common.(c|h) -- helper functions for resetting memblock;
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|-- main.c --------------. dummy physical memory definition
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|-- Makefile `- test runner
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|-- README
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|-- TODO
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|-- .gitignore
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Simulating physical memory
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==========================
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Some allocation functions clear the memory in the process, so it is required for
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memblock to track valid memory ranges. To achieve this, the test suite registers
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with memblock memory stored by test_memory struct. It is a small wrapper that
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points to a block of memory allocated via malloc. For each group of allocation
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tests, dummy physical memory is allocated, added to memblock, and then released
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at the end of the test run. The structure of a test runner checking allocation
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functions is as follows:
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int memblock_alloc_foo_checks(void)
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{
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reset_memblock_attributes(); /* data structure reset */
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dummy_physical_memory_init(); /* allocate and register memory */
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(...allocation checks...)
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dummy_physical_memory_cleanup(); /* free the memory */
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}
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There's no need to explicitly free the dummy memory from memblock via
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memblock_free() call. The entry will be erased by reset_memblock_regions(),
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called at the beginning of each test.
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Known issues
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============
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1. Requesting a specific NUMA node via memblock_alloc_node() does not work as
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intended. Once the fix is in place, tests for this function can be added.
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2. Tests for memblock_alloc_low() can't be easily implemented. The function uses
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ARCH_LOW_ADDRESS_LIMIT marco, which can't be changed to point at the low
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memory of the memory_block.
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References
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==========
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1. Boot time memory management documentation page:
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https://www.kernel.org/doc/html/latest/core-api/boot-time-mm.html
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