diff options
Diffstat (limited to 'crates/buddy_allocator/src/lib.rs')
| -rw-r--r-- | crates/buddy_allocator/src/lib.rs | 144 |
1 files changed, 117 insertions, 27 deletions
diff --git a/crates/buddy_allocator/src/lib.rs b/crates/buddy_allocator/src/lib.rs index fa86de7..441c77f 100644 --- a/crates/buddy_allocator/src/lib.rs +++ b/crates/buddy_allocator/src/lib.rs @@ -42,6 +42,8 @@ //! facilitate this, the trees are stored in an array, which forms the overall allocator. #![no_std] +extern crate std; // TODO: Remove me + mod bitvec; mod free_list; mod tree; @@ -53,7 +55,7 @@ use allocator_api2::alloc::{AllocError, Layout, LayoutError}; use contracts::requires; use core::{mem, pin::Pin, ptr::NonNull}; use vernos_physmem_free_list::FreeListAllocator; -use vernos_utils::pin::pin_project_slice_mut_iter; +use vernos_utils::pin::{pin_project_slice_mut, pin_project_slice_mut_iter}; /// A buddy allocator. #[derive(Debug)] @@ -82,37 +84,53 @@ impl< { /// Returns a buddy allocator backed by the page ranges in the free list. pub fn new( - mut free_list: FreeListAllocator<'allocator, PAGE_SIZE>, + mut free_list_alloc: FreeListAllocator<'allocator, PAGE_SIZE>, ) -> Result<BuddyAllocator<'allocator, PAGE_SIZE, PAGE_SIZE_BITS, SIZE_CLASS_COUNT>, AllocError> { assert_eq!(PAGE_SIZE, 1 << PAGE_SIZE_BITS); assert_ne!(SIZE_CLASS_COUNT, 0); + // We split up all the nodes into size-class-sized chunks here. After this, it's important + // for safety that we never split a node again -- we'll see why later. + free_list_alloc.split_to_powers_of_two_no_larger_than(1 << (SIZE_CLASS_COUNT - 1)); + // We use one contiguous region to store the free lists and all the information about each // tree (the base, the maximum order, and the bitset). We do one pass through the free list - // to find out how much storage we need, then we try to find a convenient spot to prune the + // to find out how much storage we need, then we try to find a convenient spot to steal the // storage we need from a page range in the list. let mut range_count = 0; let mut size_class_counts = [0; SIZE_CLASS_COUNT]; - for (_, mut len_pages) in free_list.iter() { - while len_pages > 0 { - let size_class = (len_pages.trailing_zeros() as usize).min(SIZE_CLASS_COUNT - 1); - range_count += 1; - size_class_counts[size_class] += 1; - len_pages -= 1 << size_class; - } + for (_, len_pages) in free_list_alloc.iter() { + assert!(len_pages.is_power_of_two()); + let size_class = len_pages.trailing_zeros() as usize; + assert!((0..SIZE_CLASS_COUNT).contains(&size_class)); + range_count += 1; + size_class_counts[size_class] += 1; } - // Lay out the metadata. The error here really ought to be impossible, because the pages in - // the free list needed to fit in there in the first place. + // Lay out the metadata. + // + // UNWRAP: The error here really ought to be impossible, because the pages in the free list + // needed to fit in there in the first place. let metadata_layout = MetadataLayout::<PAGE_SIZE, PAGE_SIZE_BITS, SIZE_CLASS_COUNT>::new( range_count, size_class_counts, ) - .map_err(|_| AllocError)?; + .unwrap(); // Allocate space for the metadata. - let metadata = free_list.allocate_zeroed(metadata_layout.layout)?; + // + // SAFETY: We need to make _absolutely_ sure nothing in the buddy allocator uses this + // memory before we have a chance to remove it from the allocator. This function guarantees + // that the returned memory won't overlap with the first page of a live node, so as long as + // we don't split a node or write past the first page of one, we should be OK. + let metadata = unsafe { + free_list_alloc.allocate_without_always_removing_the_node(metadata_layout.layout)? + }; + // SAFETY: The pointer must be valid to have been returned here. + unsafe { + metadata.cast::<u8>().write_bytes(0, metadata.len()); + } // Break out each component of the metadata. // @@ -144,15 +162,80 @@ impl< // Pin and self-link each free list. Although they're valid in a UB sense when zeroed, // they're not yet ready to use until this is done. // - // SAFETY: We never provide the ability to move out of a free list. + // SAFETY: We never provide the ability to move a free list. let mut free_lists = unsafe { Pin::new_unchecked(free_lists) }; for free_list in pin_project_slice_mut_iter(free_lists.as_mut()) { free_list.self_link(); } - // TODO: Actually initialize the trees with ranges from the allocator... + // Initialize the trees, adding subregions into the allocator as we do. We don't actually + // assign bitset offsets yet, because we're going to sort the trees by address before we + // do. (This isn't algorithmically necessary, but it makes debugging a bit easier.) + let mut i = 0; + while let Some((ptr, mut len_pages)) = free_list_alloc.pop() { + while len_pages > 0 { + let size_class = (len_pages.trailing_zeros() as usize).min(SIZE_CLASS_COUNT - 1); + trees[i].base_ptr = ptr.cast().as_ptr(); + trees[i].size_class = size_class; + i += 1; + len_pages -= 1 << size_class; + } + } + assert!( + i == trees.len() || i + 1 == trees.len(), + "found {} trees but allocated {} slots", + i, + trees.len() + ); + + // Slice the trees slice to fit how many trees actually remained, then sort them by + // address. + let trees = &mut trees[..i]; + trees.sort_by_key(|tree| tree.base_ptr as usize); + + // Compute the number of bits that belong to each tree and assign them. + let mut bitset_offset = 0; + for tree in &mut *trees { + tree.bitset_offset = bitset_offset; + bitset_offset += (1 << (tree.size_class + 1)) - 1; + } + assert!(bitset_offset <= metadata_layout.bitset_len_bits); + + // Add regions the trees should own to the free lists, excluding the subregions that + // metadata is allocated in. - // Make the buddy allocator and return. + // Since we know that the metadata was allocated at the end of the page range it was + // allocated in, we can just test the end addresses. + // + // SAFETY: This is the one-past-the-end address. + let metadata_addr_hi = + unsafe { metadata.cast::<u8>().add(metadata.len()).as_ptr() } as usize; + for tree in &mut *trees { + // SAFETY: This is the one-past-the-end address. + let tree_addr_hi = unsafe { tree.base_ptr.add(1 << tree.size_class) } as usize; + if metadata_addr_hi == tree_addr_hi { + // If the metadata was present inside the tree... TODO. + std::eprintln!("TODO"); + } else { + // Otherwise, we can take the whole range of the tree and add it to the free list. + // + // UNWRAP: The pointer must have been non-null when it was in the free-list + // allocator. + let ptr = NonNull::new(tree.base_ptr as *mut u8).unwrap(); + // SAFETY: This region is not owned or borrowed by anything else (the only thing it + // could be would be the metadata, but that's not in this tree), is of the correct + // size, and is composed of untyped memory. + unsafe { + pin_project_slice_mut(free_lists.as_mut(), tree.size_class).push(ptr); + } + + // Then, set a bit in the bitset to say that this region is present. + assert!(!bitset.get(tree.bitset_offset)); + bitset.set(tree.bitset_offset, true); + } + } + + // Make the buddy allocator's struct and return it. Ok(BuddyAllocator { free_lists, trees, @@ -165,6 +248,17 @@ impl< pub fn alloc(&mut self, size_class: usize) -> Result<NonNull<u8>, AllocError> { Err(AllocError) } + + /// Returns a subregion of a particular size class to the allocator. + /// + /// # Safety + /// + /// - `ptr` must have been returned by a call to `alloc` with the same `size_class`. + /// - `ptr` must convey ownership over the entire region. + #[requires((0..SIZE_CLASS_COUNT).contains(&size_class))] + pub unsafe fn dealloc(&mut self, ptr: NonNull<u8>, size_class: usize) { + todo!() + } } #[derive(Debug)] @@ -179,6 +273,7 @@ struct MetadataLayout< trees_len: usize, bitset_offset: usize, bitset_len: usize, + bitset_len_bits: usize, } impl<const PAGE_SIZE: usize, const PAGE_SIZE_BITS: usize, const SIZE_CLASS_COUNT: usize> @@ -186,19 +281,13 @@ impl<const PAGE_SIZE: usize, const PAGE_SIZE_BITS: usize, const SIZE_CLASS_COUNT { fn new( range_count: usize, - mut size_class_counts: [usize; SIZE_CLASS_COUNT], + size_class_counts: [usize; SIZE_CLASS_COUNT], ) -> Result<MetadataLayout<PAGE_SIZE, PAGE_SIZE_BITS, SIZE_CLASS_COUNT>, LayoutError> { let trees_len = range_count; let mut bitset_len_bits = 0; - // TODO: Is there a cleaner way to compute this? - for i in (0..size_class_counts.len()).rev() { - let count = size_class_counts[i]; - if count != 0 { - bitset_len_bits += count; - if i > 0 { - size_class_counts[i - 1] += count * 2; - } - } + for (size_class, &count) in size_class_counts.iter().enumerate() { + let bits_for_size_class = (1 << (size_class + 1)) - 1; + bitset_len_bits += bits_for_size_class * count; } let bitset_len = (bitset_len_bits + usize::BITS as usize - 1) / usize::BITS as usize; @@ -217,6 +306,7 @@ impl<const PAGE_SIZE: usize, const PAGE_SIZE_BITS: usize, const SIZE_CLASS_COUNT trees_len, bitset_offset, bitset_len, + bitset_len_bits, }) } } |