some allocator changes

src/lib.rs

@@ -2,6 +2,7 @@
 #![feature(default_alloc_error_handler)]
 #![feature(panic_info_message)]
 #![feature(asm_const)]
+#![feature(const_mut_refs)]
 #![feature(alloc_error_handler)]
 #![no_std]
 #![no_main]

src/memory/allocator.rs

@@ -1,15 +1,102 @@
+use core::alloc::GlobalAlloc;
+use core::mem;
+use core::ptr::NonNull;
 use x86_64::structures::paging::{FrameAllocator, Mapper, Page, PageTableFlags, Size4KiB};
 use x86_64::structures::paging::mapper::MapToError;
 use x86_64::VirtAddr;
+use super::Locked;
 
 pub const HEAP_START: u64 = 0x_4444_4444_0000;
 pub const HEAP_SIZE: u64 = 100 * 1024; // 100 KiB
 
-#[cfg(feature = "f_ll_alloc")]
-use linked_list_allocator::LockedHeap;
-
 #[global_allocator]
-static ALLOCATOR: LockedHeap = LockedHeap::empty();
+static ALLOCATOR: Locked<FixedSizeBlockAllocator> = Locked::new(FixedSizeBlockAllocator::new());
+
+const BLOCK_SIZES: &[usize] = &[8, 16, 32, 64, 128, 256, 512, 1024, 2048];
+
+pub struct FixedSizeBlockAllocator {
+    list_heads: [Option<&'static mut FixedSizeBlockNode>; BLOCK_SIZES.len()],
+    #[cfg(feature = "f_ll_alloc")]
+    fallback_allocator: linked_list_allocator::Heap,
+}
+
+pub struct FixedSizeBlockNode {
+    next: Option<&'static mut FixedSizeBlockNode>,
+}
+
+impl FixedSizeBlockAllocator {
+    pub const fn new() -> Self {
+        const EMPTY: Option<&'static mut FixedSizeBlockNode> = None;
+        Self {
+            list_heads: [EMPTY; BLOCK_SIZES.len()],
+            #[cfg(feature = "f_ll_alloc")]
+            fallback_allocator: linked_list_allocator::Heap::empty(),
+        }
+    }
+
+    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
+        self.fallback_allocator.init(heap_start, heap_size);
+    }
+
+    fn fallback_alloc(&mut self, layout: core::alloc::Layout) -> *mut u8 {
+        match self.fallback_allocator.allocate_first_fit(layout) {
+            Ok(ptr) => ptr.as_ptr(),
+            Err(_) => core::ptr::null_mut(),
+        }
+    }
+}
+
+unsafe impl GlobalAlloc for Locked<FixedSizeBlockAllocator> {
+    unsafe fn alloc(&self, layout: core::alloc::Layout) -> *mut u8 {
+        let mut allocator = self.lock();
+        match list_index(&layout) {
+            Some(index) => {
+                match allocator.list_heads[index].take() {
+                    Some(node) => {
+                        allocator.list_heads[index] = node.next.take();
+                        node as *mut FixedSizeBlockNode as *mut u8
+                    }
+                    None => {
+                        // no block exists in list => allocate new block
+                        let block_size = BLOCK_SIZES[index];
+                        // only works if all block sizes are a power of 2
+                        let block_align = block_size;
+                        let layout = core::alloc::Layout::from_size_align(block_size, block_align)
+                            .unwrap();
+                        allocator.fallback_alloc(layout)
+                    }
+                }
+            }
+            None => allocator.fallback_alloc(layout),
+        }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: core::alloc::Layout) {
+        let mut allocator = self.lock();
+        match list_index(&layout) {
+            Some(index) => {
+                let new_node = FixedSizeBlockNode {
+                    next: allocator.list_heads[index].take(),
+                };
+                // verify that block has size and alignment required for storing node
+                assert!(mem::size_of::<FixedSizeBlockNode>() <= BLOCK_SIZES[index]);
+                assert!(mem::align_of::<FixedSizeBlockNode>() <= BLOCK_SIZES[index]);
+                let new_node_ptr = ptr as *mut FixedSizeBlockNode;
+                new_node_ptr.write(new_node);
+                allocator.list_heads[index] = Some(&mut *new_node_ptr);
+            }
+            None => {
+                let ptr = NonNull::new(ptr).unwrap();
+                allocator.fallback_allocator.deallocate(ptr, layout);
+            }
+        }
+    }
+}
+
+fn list_index(layout: &core::alloc::Layout) -> Option<usize> {
+    let required_block_size = layout.size().max(layout.align());
+    BLOCK_SIZES.iter().position(|&s| s >= required_block_size)
+}
 
 pub fn init_heap(
     mapper: &mut impl Mapper<Size4KiB>,

src/memory/mod.rs

@@ -3,6 +3,22 @@ pub mod allocator;
 use x86_64::structures::paging::{FrameAllocator, OffsetPageTable, PageTable, PhysFrame, Size4KiB};
 use x86_64::{PhysAddr, VirtAddr};
 
+pub struct Locked<A> {
+    inner: spin::Mutex<A>,
+}
+
+impl<A> Locked<A> {
+    pub const fn new(inner: A) -> Self {
+        Locked {
+            inner: spin::Mutex::new(inner),
+        }
+    }
+
+    pub fn lock(&self) -> spin::MutexGuard<A> {
+        self.inner.lock()
+    }
+}
+
 pub unsafe fn init(phys_mem_offset: VirtAddr) -> OffsetPageTable<'static> {
     let level_4_table = active_level_4_table(phys_mem_offset);
     OffsetPageTable::new(level_4_table, phys_mem_offset)