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Philipp Oppermann
2020-01-08 17:37:40 +01:00
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blog/content/second-edition/posts/11-allocator-designs/index.md
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## Introduction ## Introduction
TODO In the [previous post] we added basic support for heap allocations to our kernel. For that, we [created a new memory region][map-heap] in the page tables and [used the `linked_list_allocator` crate][use-alloc-crate] to manage that memory. While we have a working heap now, we left most of the work to the allocator crate without understanding how it works.
## Design Goals [previous post]: @/second-edition/posts/10-heap-allocation/index.md
[map-heap]: @/second-edition/posts/10-heap-allocation/index.md#creating-a-kernel-heap
[use-alloc-crate]: @/second-edition/posts/10-heap-allocation/index.md#using-an-allocator-crate
In this post, we will show how to create our own heap allocator from scratch instead of relying on an existing allocator crate. We will discuss different allocator designs, including a simplistic _bump allocator_ and a basic _fixed-size block allocator_, and use this knowledge to implement an allocator with improved performance.
### Design Goals
The responsibility of an allocator is to manage the available heap memory. It needs to return unused memory on `alloc` calls and keep track of memory freed by `dealloc` so that it can be reused again. Most importantly, it must never hand out memory that is already in use somewhere else because this would cause undefined behavior. The responsibility of an allocator is to manage the available heap memory. It needs to return unused memory on `alloc` calls and keep track of memory freed by `dealloc` so that it can be reused again. Most importantly, it must never hand out memory that is already in use somewhere else because this would cause undefined behavior.