Merge pull request #51 from Andy-Python-Programmer/slab

mem: use slab allocator when allocating smol stuff

Author: Andy-Python-Programmer

src/aero_kernel/src/arch/x86_64/mod.rs

@@ -170,10 +170,10 @@ extern "C" fn x86_64_aero_main(boot_info: &'static StivaleStruct) -> ! {
     gdt::init_boot();
     log::info!("loaded bootstrap GDT");
 
-    let mut offset_table = paging::init(mmap_tag).unwrap();
+    paging::init(mmap_tag).unwrap();
     log::info!("loaded paging");
 
-    alloc::init_heap(&mut offset_table).expect("failed to initialize the kernel heap");
+    alloc::init_heap();
     log::info!("loaded heap");
 
     paging::init_vm_frames();

src/aero_kernel/src/mem/alloc.rs

@@ -21,93 +21,238 @@ use core::alloc;
 use core::alloc::{GlobalAlloc, Layout};
 use core::ptr::NonNull;
 
-use crate::utils::sync::Mutex;
-use linked_list_allocator::{align_up, Heap};
+use linked_list_allocator::Heap;
 
-use crate::mem::paging::*;
+use crate::utils::sync::Mutex;
 use crate::AERO_SYSTEM_ALLOCATOR;
 
 use super::paging::FRAME_ALLOCATOR;
 use super::AddressSpace;
+use crate::mem::paging::*;
 
 const HEAP_MAX_SIZE: usize = 128 * 1024 * 1024; // 128 GiB
 const HEAP_START: usize = 0xfffff80000000000;
 const HEAP_END: usize = HEAP_START + HEAP_MAX_SIZE;
 
-pub struct LockedHeap(Mutex<Heap>);
+#[repr(C)]
+struct SlabHeader {
+    ptr: *mut Slab,
+}
 
-impl LockedHeap {
-    /// Creates a new uninitialized instance of the kernel
-    /// global allocator.
-    #[inline]
-    pub const fn new_uninit() -> Self {
-        Self(Mutex::new(Heap::empty()))
+/// The slab is the primary unit of currency in the slab allocator.
+struct Slab {
+    size: usize,
+    first_free: usize,
+}
+
+impl Slab {
+    const fn new(size: usize) -> Self {
+        Self {
+            size,
+            first_free: 0,
+        }
     }
 
-    /// Allocate memory as described by the given `layout`.
-    ///
-    /// Returns a pointer to newly-allocated memory, or null to indicate
-    /// allocation failure.
-    unsafe fn allocate(&self, layout: alloc::Layout) -> Result<NonNull<u8>, ()> {
-        // SAFETY: We we need to be careful to not cause a deadlock as the interrupt
-        // handlers utilize the heap and might interrupt an in-progress allocation. So, we
-        // lock the interrupts during the allocation.
-        let mut heap = self.0.lock_irq();
+    fn init(&mut self) {
+        unsafe {
+            let frame: PhysFrame<Size4KiB> = FRAME_ALLOCATOR
+                .allocate_frame()
+                .expect("slab_init: failed to allocate frame");
+
+            self.first_free = frame.start_address().as_u64() as usize;
+            self.first_free += crate::PHYSICAL_MEMORY_OFFSET.as_u64() as usize;
+        }
+
+        let hdr_size = core::mem::size_of::<SlabHeader>() as u64;
+        let aligned_hdr_size = align_up(hdr_size, self.size as u64) as usize;
 
-        heap.allocate_first_fit(layout).or_else(|_| {
-            let heap_top = heap.top();
-            let size = align_up(layout.size(), 0x1000);
+        let avl_size = Size4KiB::SIZE as usize - aligned_hdr_size;
 
-            // Check if our heap has not increased beyond the maximum allowed size.
-            if heap_top + size > HEAP_END {
-                panic!("The heap size has increased more then {:#x}", HEAP_END)
+        let slab_ptr = unsafe { &mut *(self.first_free as *mut SlabHeader) };
+        slab_ptr.ptr = self as *mut Slab;
+
+        self.first_free += aligned_hdr_size;
+
+        let arr_ptr = self.first_free as *mut usize;
+        let array = unsafe { core::slice::from_raw_parts_mut(arr_ptr, avl_size) };
+
+        // A slab is built by allocating a 4KiB page, placing the slab data at
+        // the end, and dividing the rest into equal-size buffers:
+        //
+        // ------------------------------------------------------
+        // | buffer | buffer | buffer | buffer | slab header
+        // ------------------------------------------------------
+        //                         one page
+        let max = avl_size / self.size - 1;
+        let fact = self.size / 8;
+
+        for i in 0..max {
+            unsafe {
+                array[i * fact] = array.as_ptr().add((i + 1) * fact) as usize;
             }
+        }
+
+        array[max * fact] = 0;
+    }
+
+    fn alloc(&mut self) -> *mut u8 {
+        if self.first_free == 0 {
+            self.init();
+        }
+
+        let old_free = self.first_free as *mut usize;
+
+        unsafe {
+            self.first_free = *old_free;
+        }
+
+        old_free as *mut u8
+    }
+
+    fn dealloc(&mut self, ptr: *mut u8) {
+        if ptr == core::ptr::null_mut() {
+            panic!("dealloc: attempted to free a nullptr")
+        }
+
+        let new_head = ptr as *mut usize;
+
+        unsafe {
+            *new_head = self.first_free;
+        }
+
+        self.first_free = new_head as usize;
+    }
+}
+
+struct ProtectedAllocator {
+    slabs: [Slab; 10],
+    linked_list_heap: Heap,
+}
+
+struct Allocator {
+    inner: Mutex<ProtectedAllocator>,
+}
 
-            // Else we just have to extend the heap.
-            let mut address_space = AddressSpace::this();
-            let mut offset_table = address_space.offset_page_table();
-
-            let page_range = {
-                let heap_start = VirtAddr::new(heap_top as _);
-                let heap_end = heap_start + size - 1u64;
-
-                let heap_start_page: Page = Page::containing_address(heap_start);
-                let heap_end_page = Page::containing_address(heap_end);
-
-                Page::range_inclusive(heap_start_page, heap_end_page)
-            };
-
-            for page in page_range {
-                let frame = unsafe {
-                    FRAME_ALLOCATOR
-                        .allocate_frame()
-                        .expect("Failed to allocate frame to extend heap")
-                };
-
-                unsafe {
-                    offset_table.map_to(
-                        page,
-                        frame,
-                        PageTableFlags::PRESENT | PageTableFlags::WRITABLE,
-                        &mut FRAME_ALLOCATOR,
-                    )
-                }
-                .expect("Failed to map frame to extend the heap")
-                .flush();
+impl Allocator {
+    const fn new() -> Self {
+        Self {
+            inner: Mutex::new(ProtectedAllocator {
+                slabs: [
+                    Slab::new(8),
+                    Slab::new(16),
+                    Slab::new(24),
+                    Slab::new(32),
+                    Slab::new(48),
+                    Slab::new(64),
+                    Slab::new(128),
+                    Slab::new(256),
+                    Slab::new(512),
+                    Slab::new(1024),
+                ],
+
+                linked_list_heap: Heap::empty(),
+            }),
+        }
+    }
+
+    fn alloc(&self, layout: Layout) -> *mut u8 {
+        let mut inner = self.inner.lock_irq();
+
+        let slab = inner
+            .slabs
+            .iter_mut()
+            .find(|slab| slab.size >= layout.size());
+
+        if let Some(slab) = slab {
+            slab.alloc()
+        } else {
+            inner
+                .linked_list_heap
+                .allocate_first_fit(layout)
+                .or_else(|_| {
+                    let heap_top = inner.linked_list_heap.top();
+                    let size = align_up(layout.size() as u64, 0x1000);
+
+                    // Check if our heap has not increased beyond the maximum allowed size.
+                    if heap_top + size as usize > HEAP_END {
+                        panic!("the heap size has increased more then {:#x}", HEAP_END)
+                    }
+
+                    // Else we just have to extend the heap.
+                    let mut address_space = AddressSpace::this();
+                    let mut offset_table = address_space.offset_page_table();
+
+                    let page_range = {
+                        let heap_start = VirtAddr::new(heap_top as _);
+                        let heap_end = heap_start + size - 1u64;
+
+                        let heap_start_page: Page = Page::containing_address(heap_start);
+                        let heap_end_page = Page::containing_address(heap_end);
+
+                        Page::range_inclusive(heap_start_page, heap_end_page)
+                    };
+
+                    for page in page_range {
+                        let frame = unsafe {
+                            FRAME_ALLOCATOR
+                                .allocate_frame()
+                                .expect("Failed to allocate frame to extend heap")
+                        };
+
+                        unsafe {
+                            offset_table.map_to(
+                                page,
+                                frame,
+                                PageTableFlags::PRESENT | PageTableFlags::WRITABLE,
+                                &mut FRAME_ALLOCATOR,
+                            )
+                        }
+                        .expect("Failed to map frame to extend the heap")
+                        .flush();
+                    }
+
+                    unsafe {
+                        inner.linked_list_heap.extend(size as usize); // Now extend the heap.
+                        inner.linked_list_heap.allocate_first_fit(layout) // And try again.
+                    }
+                })
+                .expect("alloc: memory exhausted")
+                .as_ptr()
+        }
+    }
+
+    fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        let mut inner = self.inner.lock_irq();
+
+        let size = layout.size();
+
+        if size >= Size4KiB::SIZE as usize {
+            unsafe {
+                inner
+                    .linked_list_heap
+                    .deallocate(NonNull::new_unchecked(ptr), layout);
             }
 
-            heap.extend(size); // Now extend the heap.
-            heap.allocate_first_fit(layout) // And try again.
-        })
+            return;
+        }
+
+        let slab_header = (ptr as usize & !(0xfff)) as *mut SlabHeader;
+
+        let slab_header = unsafe { &mut *slab_header };
+        let slab = unsafe { &mut *slab_header.ptr };
+
+        slab.dealloc(ptr);
     }
+}
+
+pub struct LockedHeap(Allocator);
 
-    /// Initializes an empty heap.
-    ///
-    /// ## Safety
-    /// This function should only be called once and the provided `start` address
-    /// should be a valid address.
-    unsafe fn init(&self, start: usize, size: usize) {
-        self.0.lock().init(start, size);
+impl LockedHeap {
+    /// Creates a new uninitialized instance of the kernel
+    /// global allocator.
+    #[inline]
+    pub const fn new_uninit() -> Self {
+        Self(Allocator::new())
     }
 }
 
@@ -220,7 +365,10 @@ unsafe impl GlobalAlloc for LockedHeap {
         // necessary and sufficient.
         debug_assert!(layout.size() < usize::MAX - (layout.align() - 1));
 
-        let ptr = self.allocate(layout).unwrap().as_ptr();
+        // SAFETY: We we need to be careful to not cause a deadlock as the interrupt
+        // handlers utilize the heap and might interrupt an in-progress allocation. So, we
+        // lock the interrupts during the allocation.
+        let ptr = self.0.alloc(layout);
 
         #[cfg(feature = "kmemleak")]
         kmemleak::MEM_LEAK_CATCHER.track_caller(ptr, layout);
@@ -235,9 +383,7 @@ unsafe impl GlobalAlloc for LockedHeap {
         #[cfg(feature = "kmemleak")]
         kmemleak::MEM_LEAK_CATCHER.unref(ptr);
 
-        self.0
-            .lock_irq()
-            .deallocate(NonNull::new_unchecked(ptr), layout)
+        self.0.dealloc(ptr, layout)
     }
 }
 
@@ -251,29 +397,33 @@ fn alloc_error_handler(layout: alloc::Layout) -> ! {
 }
 
 /// Initialize the heap at the [HEAP_START].
-pub fn init_heap(offset_table: &mut OffsetPageTable) -> Result<(), MapToError<Size4KiB>> {
-    let frame: PhysFrame = unsafe {
-        FRAME_ALLOCATOR
-            .allocate_frame()
-            .ok_or(MapToError::FrameAllocationFailed)?
-    };
-
+pub fn init_heap() {
     unsafe {
-        offset_table.map_to(
-            Page::containing_address(VirtAddr::new(HEAP_START as _)),
-            frame,
-            PageTableFlags::PRESENT | PageTableFlags::WRITABLE,
-            &mut FRAME_ALLOCATOR,
-        )
-    }?
-    .flush();
+        let mut address_space = AddressSpace::this();
+        let mut offset_table = address_space.offset_page_table();
 
-    unsafe {
-        AERO_SYSTEM_ALLOCATOR.init(HEAP_START, 4096);
+        let frame: PhysFrame = FRAME_ALLOCATOR
+            .allocate_frame()
+            .expect("init_heap: failed to allocate frame for the linked list allocator");
+
+        offset_table
+            .map_to(
+                Page::containing_address(VirtAddr::new(HEAP_START as _)),
+                frame,
+                PageTableFlags::PRESENT | PageTableFlags::WRITABLE,
+                &mut FRAME_ALLOCATOR,
+            )
+            .expect("init_heap: failed to initialize the heap")
+            .flush();
+
+        AERO_SYSTEM_ALLOCATOR
+            .0
+            .inner
+            .lock_irq()
+            .linked_list_heap
+            .init(HEAP_START, Size4KiB::SIZE as usize);
     }
 
     #[cfg(feature = "kmemleak")]
     kmemleak::MEM_LEAK_CATCHER.init();
-
-    Ok(())
 }