post-11 heap allocator designs

src/allocator.rs

@@ -1,17 +1,25 @@
 use alloc::alloc::{GlobalAlloc, Layout};
 use core::ptr::null_mut;
-use x86_64:: {
+use x86_64::{
-    structures::paging:: {
+    structures::paging::{
-        FrameAllocator,
+        mapper::MapToError, FrameAllocator, Mapper, Page, PageTableFlags, Size4KiB,
-        mapper::MapToError,
-        Mapper,
-        Page,
-        PageTableFlags,
-        Size4KiB,
     },
     VirtAddr,
 };
 
+pub mod bump;
+pub mod fixed_size_block;
+pub mod linked_list;
+
+
+// use bump::BumpAllocator;
+use fixed_size_block::FixedSizeBlockAllocator;
+// use linked_list::LinkedListAllocator;
+
+#[global_allocator]
+static ALLOCATOR: Locked<FixedSizeBlockAllocator> =
+    Locked::new(FixedSizeBlockAllocator::new());
+
 pub const HEAP_START: usize = 0x_4444_4444_0000;
 pub const HEAP_SIZE: usize = 100 * 1024; // 100 KiB
 
@@ -49,8 +57,33 @@ pub fn init_heap(
     }
 
     unsafe {
-        super::ALLOCATOR.lock().init(HEAP_START, HEAP_SIZE);
+        ALLOCATOR.lock().init(HEAP_START, HEAP_SIZE);
     }
 
     Ok(())
 }
+
+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()
+    }
+}
+
+fn align_up(addr: usize, align: usize) -> usize {
+    let remainder = addr % align;
+    if remainder == 0 {
+        addr // addr already aligned
+    } else {
+        addr - remainder + align
+    }
+}

src/allocator/bump.rs

@@ -0,0 +1,58 @@
+use super::{align_up, Locked};
+use alloc::alloc::{GlobalAlloc, Layout};
+use core::ptr;
+
+pub struct BumpAllocator {
+    heap_start: usize,
+    heap_end: usize,
+    next: usize,
+    allocations: usize,
+}
+
+impl BumpAllocator {
+    ///Creates a new empty bump allocator
+    pub const fn new() -> Self {
+        BumpAllocator {
+            heap_start: 0,
+            heap_end: 0,
+            next: 0,
+            allocations: 0,
+        }
+    }
+
+    /// Initializes the bump allocator with the given heap bounds.
+    ///
+    /// This method is unsafe because the caller must ensure that the given
+    /// memory range is unused. Also, this method must be called only once.
+    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
+        self.heap_start = heap_start;
+        self.heap_end = heap_start + heap_size;
+        self.next = heap_start;
+    }
+}
+
+unsafe impl GlobalAlloc for Locked<BumpAllocator> {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        let mut bump = self.lock(); // get a mutable reference
+
+        let alloc_start = align_up(bump.next, layout.align());
+        let alloc_end = alloc_start + layout.size();
+
+        if alloc_end > bump.heap_end {
+            ptr::null_mut() // out of memory
+        } else {
+            bump.next = alloc_end;
+            bump.allocations += 1;
+            alloc_start as *mut u8
+        }
+    }
+
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {
+        let mut bump = self.lock(); // get a mutable reference
+
+        bump.allocations -= 1;
+        if bump.allocations == 0 {
+            bump.next = bump.heap_start;
+        }
+    }
+}

src/allocator/fixed_size_block.rs

@@ -0,0 +1,100 @@
+use alloc::alloc::{GlobalAlloc, Layout};
+use core::{mem, ptr};
+use super::Locked;
+
+struct ListNode {
+    next: Option<&'static mut ListNode>,
+}
+
+/// The block sizes to use.
+///
+/// The sizes must each be a power of 2 because they are also used as
+/// the block alignment (alignments must be always powers of 2).
+const BLOCK_SIZES: &[usize] = &[8, 16, 32, 64, 128, 256, 512, 1024, 2048];
+
+pub struct FixedSizeBlockAllocator {
+    list_heads: [Option<&'static mut ListNode>; BLOCK_SIZES.len()],
+    fallback_allocator: linked_list_allocator::Heap,
+}
+
+impl FixedSizeBlockAllocator {
+    /// Creates an empty FixedSizeBlockAllocator.
+    pub const fn new() -> Self {
+        FixedSizeBlockAllocator {
+            list_heads: [None; BLOCK_SIZES.len()],
+            fallback_allocator: linked_list_allocator::Heap::empty(),
+        }
+    }
+
+    /// Initialize the allocator with the given heap bounds.
+    ///
+    /// This function is unsafe because the caller must guarantee that the given
+    /// heap bounds are valid and that the heap is unused. This method must be
+    /// called only once.
+    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
+        self.fallback_allocator.init(heap_start, heap_size);
+    }
+
+    /// Allocates using the fallback allocator.
+    fn fallback_alloc(&mut self, layout: Layout) -> *mut u8 {
+        match self.fallback_allocator.allocate_first_fit(layout) {
+            Ok(ptr) => ptr.as_ptr(),
+            Err(_) => ptr::null_mut(),
+        }
+    }
+}
+
+fn list_index(layout: &Layout) -> Option<usize> {
+    let required_block_size = layout.size().max(layout.align());
+    BLOCK_SIZES.iter().position(|&s| s >= required_block_size)
+}
+
+unsafe impl GlobalAlloc for Locked<FixedSizeBlockAllocator> {
+    unsafe fn alloc(&self, layout: 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 ListNode 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 = 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: Layout) {
+        let mut allocator = self.lock();
+        match list_index(&layout) {
+            Some(index) => {
+                let new_node = ListNode {
+                    next: allocator.list_heads[index].take(),
+                };
+
+                // verify that block has size and alignment required for storing node
+                assert!(mem::size_of::<ListNode>() <= BLOCK_SIZES[index]);
+                assert!(mem::align_of::<ListNode>() <= BLOCK_SIZES[index]);
+
+                let new_node_ptr = ptr as *mut ListNode;
+                new_node_ptr.write(new_node);
+                allocator.list_heads[index] = Some(&mut *new_node_ptr);
+            }
+            None => {
+                let ptr = ptr::NonNull::new(ptr).unwrap();
+                allocator.fallback_allocator.deallocate(ptr, layout);
+            }
+        }
+    }
+}

src/allocator/linked_list.rs

@@ -0,0 +1,148 @@
+use super::{align_up, Locked};
+use alloc::alloc::{GlobalAlloc, Layout};
+use core::{mem, ptr};
+
+struct ListNode {
+    size: usize,
+    next: Option<&'static mut ListNode>,
+}
+
+impl ListNode {
+    const fn new(size: usize) -> Self {
+        ListNode { size, next: None }
+    }
+
+    fn start_addr(&self) -> usize {
+        self as *const Self as usize
+    }
+
+    fn end_addr(&self) -> usize {
+        self.start_addr() + self.size
+    }
+}
+
+pub struct LinkedListAllocator {
+    head: ListNode,
+}
+
+impl LinkedListAllocator {
+    /// Creates an empty LinkedListAllocator.
+    pub const fn new() -> Self {
+        Self {
+            head: ListNode::new(0),
+        }
+    }
+
+    /// Initialize the allocator with the given heap bounds.
+    ///
+    /// This function is unsafe because the caller must guarantee that the given
+    /// heap bounds are valid and that the heap is unused. This method must be
+    /// called only once.
+    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
+        self.add_free_region(heap_start, heap_size);
+    }
+
+    /// Adds the given memory region to the front of the list
+    unsafe fn add_free_region(&mut self, addr: usize, size: usize) {
+        // ensure that the freed region is capable of holding ListNode
+        assert!(align_up(addr, mem::align_of::<ListNode>()) == addr);
+        assert!(size >= mem::size_of::<ListNode>());
+
+        // create a new list node and append it at the start of the list
+        let mut node = ListNode::new(size);
+        node.next = self.head.next.take();
+        let node_ptr = addr as *mut ListNode;
+        node_ptr.write(node);
+        self.head.next = Some(&mut *node_ptr)
+    }
+
+    /// Looks for a free region with the given size and alignment and removes
+    /// it from the list.
+    ///
+    /// Returns a tuple of the list node and the start address of the allocation
+    fn find_region(&mut self, size: usize, align: usize) -> Option<(&'static mut ListNode, usize)> {
+        // reference to the current list node, updated for each iteration
+        let mut current = &mut self.head;
+        // look for a large enough memory region in linked list
+        while let Some(ref mut region) = current.next {
+            if let Ok(alloc_start) = Self::alloc_from_region(&region, size, align) {
+                // region suitable for allocation -> remove node from list
+                let next = region.next.take();
+                let ret = Some((current.next.take().unwrap(), alloc_start));
+                current.next = next;
+                return ret;
+            } else {
+                // region not suitable -> continue with next region
+                current = current.next.as_mut().unwrap();
+            }
+        }
+
+        // no suitable region found
+        None
+    }
+
+    /// Try to use the given region for an allocation with given size and
+    /// alignment.
+    ///
+    /// Returns the allocation start address on success.
+    fn alloc_from_region(region: &ListNode, size: usize, align: usize) -> Result<usize, ()> {
+        let alloc_start = align_up(region.start_addr(), align);
+        let alloc_end = alloc_start + size;
+
+        if alloc_end > region.end_addr() {
+            // region too small
+            return Err(());
+        }
+
+        let excess_size = region.end_addr() - alloc_end;
+        if excess_size > 0 && excess_size < mem::size_of::<ListNode>() {
+            // rest of region too small to hold a ListNode (required because the
+            // allocation splits the region in a used and a free part)
+            return Err(());
+        }
+
+        // region suitable for allocation
+        Ok(alloc_start)
+    }
+
+    /// Adjust the given layout so that the resulting allocated memory
+    /// region is also capable of storing a `ListNode`.
+    ///
+    /// Returns the adjusted size and alignment as a (size, align) tuple.
+    fn size_align(layout: Layout) -> (usize, usize) {
+        let layout = layout
+            .align_to(mem::align_of::<ListNode>())
+            .expect("adjusting alignment failed")
+            .pad_to_align();
+
+        let size = layout.size().max(mem::size_of::<ListNode>());
+
+        (size, layout.align())
+    }
+}
+
+unsafe impl GlobalAlloc for Locked<LinkedListAllocator> {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        // perform layout adjustments
+        let (size, align) = LinkedListAllocator::size_align(layout);
+        let mut allocator = self.inner.lock();
+
+        if let Some((region, alloc_start)) = allocator.find_region(size, align) {
+            let alloc_end = alloc_start + size;
+            let excess_size = region.end_addr() - alloc_end;
+            if excess_size > 0 {
+                allocator.add_free_region(alloc_end, excess_size);
+            }
+            alloc_start as *mut u8
+        } else {
+            ptr::null_mut()
+        }
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        // perform layout adjustments
+        let (size, _) = LinkedListAllocator::size_align(layout);
+
+        self.inner.lock().add_free_region(ptr as usize, size)
+    }
+}

src/lib.rs

@@ -1,8 +1,11 @@
 #![no_std]
 #![cfg_attr(test, no_main)]
-#![feature(alloc_error_handler)]
-#![feature(custom_test_frameworks)]
 #![feature(abi_x86_interrupt)]
+#![feature(alloc_error_handler)]
+#![feature(alloc_layout_extra)]
+#![feature(const_fn)]
+#![feature(const_in_array_repeat_expressions)]
+#![feature(custom_test_frameworks)]
 #![test_runner(crate::test_runner)]
 #![reexport_test_harness_main = "test_main"]
 
@@ -17,8 +20,8 @@ use bootloader::{entry_point, BootInfo};
 #[cfg(test)]
 entry_point!(test_kernel_main);
 
-#[global_allocator]
+// #[global_allocator]
-static ALLOCATOR: LockedHeap = LockedHeap::empty();
+// static ALLOCATOR: LockedHeap = LockedHeap::empty();
 
 #[alloc_error_handler]
 fn alloc_error_handler(layout: alloc::alloc::Layout) -> ! {

src/main.rs

@@ -6,12 +6,7 @@
 
 extern crate alloc;
 
-use alloc::{
+use alloc::{boxed::Box, rc::Rc, vec, vec::Vec};
-    boxed::Box,
-    vec,
-    vec::Vec,
-    rc::Rc,
-};
 use core::panic::PanicInfo;
 
 use blog_os::println;
@@ -42,12 +37,9 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
     blog_os::init();
 
     let mut mapper = unsafe { memory::init(VirtAddr::new(boot_info.physical_memory_offset)) };
-    let mut frame_allocator = unsafe {
+    let mut frame_allocator = unsafe { BootInfoFrameAllocator::init(&boot_info.memory_map) };
-        BootInfoFrameAllocator::init(&boot_info.memory_map)
-    };
 
-    allocator::init_heap(&mut mapper, &mut frame_allocator)
+    allocator::init_heap(&mut mapper, &mut frame_allocator).expect("heap initialization failed");
-        .expect("heap initialization failed");
 
     // allocate a number on the heap
     let heap_value = Box::new(41);
@@ -63,9 +55,15 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
     // create a reference counted vector -> will be freed when count reaches 0
     let reference_counted = Rc::new(vec![1, 2, 3]);
     let cloned_reference = reference_counted.clone();
-    println!("current reference count is {}", Rc::strong_count(&cloned_reference));
+    println!(
+        "current reference count is {}",
+        Rc::strong_count(&cloned_reference)
+    );
     core::mem::drop(reference_counted);
-    println!("reference count is {} now", Rc::strong_count(&cloned_reference));
+    println!(
+        "reference count is {} now",
+        Rc::strong_count(&cloned_reference)
+    );
 
     #[cfg(test)]
     test_main();

tests/heap_allocation.rs

@@ -8,6 +8,7 @@ extern crate alloc;
 
 use alloc::boxed::Box;
 use alloc::vec::Vec;
+use blog_os::allocator::HEAP_SIZE;
 use blog_os::{serial_print, serial_println};
 use bootloader::{entry_point, BootInfo};
 use core::panic::PanicInfo;
@@ -22,11 +23,8 @@ fn main(boot_info: &'static BootInfo) -> ! {
     blog_os::init();
     let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset);
     let mut mapper = unsafe { memory::init(phys_mem_offset) };
-    let mut frame_allocator = unsafe {
+    let mut frame_allocator = unsafe { BootInfoFrameAllocator::init(&boot_info.memory_map) };
-        BootInfoFrameAllocator::init(&boot_info.memory_map)
+    allocator::init_heap(&mut mapper, &mut frame_allocator).expect("heap initialization failed");
-    };
-    allocator::init_heap(&mut mapper, &mut frame_allocator)
-        .expect("heap initialization failed");
 
     test_main();
 
@@ -67,3 +65,15 @@ fn many_boxes() {
     }
     serial_println!("[ok]");
 }
+
+#[test_case]
+fn many_boxes_long_lived() {
+    serial_print!("many_boxes_long_lived... ");
+    let long_lived = Box::new(1);
+    for i in 0..HEAP_SIZE {
+        let x = Box::new(i);
+        assert_eq!(*x, i);
+    }
+    assert_eq!(*long_lived, 1);
+    serial_println!("[ok]");
+}