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free list allocator

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This commit is contained in:
Corwin Kuiper 2021-08-21 11:07:53 +01:00
parent e5f331587f
commit 6523a3c6b8
1 changed files with 31 additions and 45 deletions
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76
agb/src/agb_alloc/block_allocator.rs
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@ -6,22 +6,26 @@ use crate::interrupt::Mutex;
use super::bump_allocator::BumpAllocator;
struct Block {
used: bool,
size: usize,
next: Option<NonNull<Block>>,
}
impl Block {
pub unsafe fn from_data_ptr(data_ptr: *mut u8, layout: Layout) -> *mut Block {
pub fn either_layout(layout: Layout) -> Layout {
let block_layout = Layout::new::<Block>();
let (_, offset) = block_layout.extend(layout).expect("Overflow on allocation");
data_ptr.sub(offset).cast()
let aligned_to = layout
.align_to(block_layout.align())
.expect("too large allocation");
Layout::from_size_align(
block_layout.size().max(aligned_to.size()),
aligned_to.align(),
)
.expect("too large allocation")
}
}
struct BlockAllocatorState {
first_block: Option<NonNull<Block>>,
last_block: Option<NonNull<Block>>,
first_free_block: Option<NonNull<Block>>,
}
pub(crate) struct BlockAllocator {
@ -34,15 +38,13 @@ impl BlockAllocator {
Self {
inner_allocator: BumpAllocator::new(),
state: Mutex::new(BlockAllocatorState {
first_block: None,
last_block: None,
first_free_block: None,
}),
}
}
unsafe fn new_block(&self, layout: Layout) -> *mut u8 {
let block_layout = Layout::new::<Block>();
let (overall_layout, offset) = block_layout.extend(layout).expect("Overflow on allocation");
let overall_layout = Block::either_layout(layout);
let block_ptr = self.inner_allocator.alloc(overall_layout);
@ -50,49 +52,27 @@ impl BlockAllocator {
return core::ptr::null_mut();
}
let block_ptr = NonNull::new_unchecked(block_ptr).cast();
let mut state = self.state.lock();
*block_ptr.cast::<Block>().as_mut() = Block {
used: true,
next: None,
};
state.first_block.get_or_insert(block_ptr);
if let Some(last_block) = state.last_block {
last_block.cast::<Block>().as_mut().next = Some(block_ptr);
}
state.last_block = Some(block_ptr);
block_ptr.as_ptr().cast::<u8>().add(offset)
block_ptr
}
}
unsafe impl GlobalAlloc for BlockAllocator {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
// find a block that this current request fits in
let block_layout = Layout::new::<Block>();
let (full_layout, offset) = block_layout.extend(layout).unwrap();
let full_layout = Block::either_layout(layout);
{
let state = self.state.lock();
let mut current_block = state.first_block;
let mut state = self.state.lock();
let mut current_block = state.first_free_block;
let mut list_ptr = &mut state.first_free_block;
while let Some(mut curr) = current_block {
let mut curr_block = curr.as_mut();
if !curr_block.used {
if let Some(next) = curr_block.next {
let size = next.cast::<u8>().as_ptr().offset_from(curr.as_ptr().cast());
if size >= full_layout.size() as isize {
curr_block.used = true;
return curr.as_ptr().cast::<u8>().add(offset);
}
}
let curr_block = curr.as_mut();
if curr_block.size >= full_layout.size() {
*list_ptr = curr_block.next;
return curr.as_ptr().cast();
}
current_block = curr_block.next;
list_ptr = &mut curr_block.next;
}
}
@ -100,7 +80,13 @@ unsafe impl GlobalAlloc for BlockAllocator {
}
unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
let block = Block::from_data_ptr(ptr, layout);
(*block).used = false;
let new_layout = Block::either_layout(layout);
let mut state = self.state.lock();
let new_block_content = Block {
size: new_layout.size(),
next: state.first_free_block,
};
*ptr.cast() = new_block_content;
state.first_free_block = NonNull::new(ptr.cast());
}
}