103 lines
3.7 KiB
Rust
103 lines
3.7 KiB
Rust
use super::Locked;
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use alloc::alloc::{GlobalAlloc, Layout};
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use core::{
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mem,
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ptr::{self, NonNull},
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};
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/// The block sizes to use.
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///
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/// The sizes must each be power of 2 because they are also used as
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/// the block alignment (alignments must be always powers of 2).
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const BLOCK_SIZES: &[usize] = &[8, 16, 32, 64, 128, 256, 512, 1024, 2048];
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/// Choose an appropriate block size for the given layout.
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///
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/// Returns an index into the `BLOCK_SIZES` array.
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fn list_index(layout: &Layout) -> Option<usize> {
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let required_block_size = layout.size().max(layout.align());
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BLOCK_SIZES.iter().position(|&s| s >= required_block_size)
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}
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struct ListNode {
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next: Option<&'static mut ListNode>,
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}
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pub struct FixedSizeBlockAllocator {
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list_heads: [Option<&'static mut ListNode>; BLOCK_SIZES.len()],
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fallback_allocator: linked_list_allocator::Heap,
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}
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impl FixedSizeBlockAllocator {
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/// Creates an empty FixedSizeBlockAllocator.
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pub const fn new() -> Self {
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FixedSizeBlockAllocator {
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list_heads: [None; BLOCK_SIZES.len()],
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fallback_allocator: linked_list_allocator::Heap::empty(),
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}
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}
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/// Initialize the allocator with the given heap bounds.
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///
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/// This function is unsafe because the caller must guarantee that the given
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/// heap bounds are valid and that the heap is unused. This method must be
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/// called only once.
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pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
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self.fallback_allocator.init(heap_start, heap_size);
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}
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/// Allocates using the fallback allocator.
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fn fallback_alloc(&mut self, layout: Layout) -> *mut u8 {
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match self.fallback_allocator.allocate_first_fit(layout) {
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Ok(ptr) => ptr.as_ptr(),
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Err(_) => ptr::null_mut(),
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}
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}
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}
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unsafe impl GlobalAlloc for Locked<FixedSizeBlockAllocator> {
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unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
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let mut allocator = self.lock();
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match list_index(&layout) {
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Some(index) => {
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match allocator.list_heads[index].take() {
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Some(node) => {
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allocator.list_heads[index] = node.next.take();
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node as *mut ListNode as *mut u8
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}
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None => {
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// no block exists in list => allocate new block
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let block_size = BLOCK_SIZES[index];
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// only works if all block sizes are a power of 2
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let block_align = block_size;
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let layout = Layout::from_size_align(block_size, block_align).unwrap();
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allocator.fallback_alloc(layout)
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}
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}
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}
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None => allocator.fallback_alloc(layout),
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}
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}
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unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
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let mut allocator = self.lock();
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match list_index(&layout) {
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Some(index) => {
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let new_node = ListNode {
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next: allocator.list_heads[index].take(),
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};
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// verify that block has size and alignment required for storing node
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assert!(mem::size_of::<ListNode>() <= BLOCK_SIZES[index]);
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assert!(mem::align_of::<ListNode>() <= BLOCK_SIZES[index]);
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let new_node_ptr = ptr as *mut ListNode;
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new_node_ptr.write(new_node);
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allocator.list_heads[index] = Some(&mut *new_node_ptr);
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}
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None => {
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let ptr = NonNull::new(ptr).unwrap();
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allocator.fallback_allocator.deallocate(ptr, layout);
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}
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}
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}
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}
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