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Memory Allocation: Difference between revisions
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It's not always desirable or practical to write your own memory allocator. Writing an efficient memory allocator can be an entire project in itself and fortunately it's extremely easy to port an existing memory allocator to your OS (to run in either kernel or user space). The advantages of using an existing memory allocator are; porting one is much faster than writing your own especially when you want to focus on other areas of your OS, it is likely to be well-tested so you do not have to debug the memory allocator, it takes a minimal amount of work to port it, and finally, someone else has down the hard work to make it fast, scalable, stable, etc.
Porting a memory allocator is fairly simple to do. Most of them are no more than one source and/or header file. The functionality you must hook is for allocating and freeing pages to your program, so the memory allocator has memory to work with.
There are
*void
▲There are also an alternative pair of hooks that some memory allocators use which allow the allocator to request memory from the kernel in terms of 'pages'. These memory allocators will have a constant stored somewhere in the source on how many large a page is (e.g. '#define PAGE_SIZE 4096' for 4KB pages) so the allocator knows how many pages to request at a time. With these allocators you must hook/implement:
*void free_page(void *start, size_t pages) - Frees 'pages' consecutive pages in virtual memory from 'start' back to the kernel.
▲*void free_page(void *start, int pages) - Frees 'pages' consecutive pages in virtual memory from 'start' back to the kernel.
In addition, some memory allocators will require you to hook locking functionality to ensure critical sections of the memory allocator aren't executed simultaneously by multiple threads. Typically the functions will appear like;
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