Jeremy Soller
322 lines
10 KiB
Rust
322 lines
10 KiB
Rust
use alloc::vec::Vec;
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use core::{fmt, mem, ops, slice};
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use endian_num::Le;
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use crate::{BlockAddr, BlockLevel, BlockMeta, BlockPtr, BlockTrait, BLOCK_SIZE};
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pub const ALLOC_LIST_ENTRIES: usize =
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(BLOCK_SIZE as usize - mem::size_of::<BlockPtr<AllocList>>()) / mem::size_of::<AllocEntry>();
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/// The RedoxFS block allocator. This struct manages all "data" blocks in RedoxFS
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/// (i.e, all blocks that aren't reserved or part of the header chain).
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///
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/// [`Allocator`] can allocate blocks of many "levels"---that is, it can
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/// allocate multiple consecutive [`BLOCK_SIZE`] blocks in one operation.
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///
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/// This reduces the amount of memory that the [`Allocator`] uses:
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/// Instead of storing the index of each free [`BLOCK_SIZE`] block,
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/// the `levels` array can keep track of higher-level blocks, splitting
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/// them when a smaller block is requested.
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///
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/// Higher-level blocks also allow us to more efficiently allocate memory
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/// for large files.
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#[derive(Clone, Default)]
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pub struct Allocator {
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/// This array keeps track of all free blocks of each level,
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/// and is initialized using the AllocList chain when we open the filesystem.
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///
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/// Every element of the outer array represents a block level:
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/// - item 0: free level 0 blocks (with size [`BLOCK_SIZE`])
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/// - item 1: free level 1 blocks (with size 2*[`BLOCK_SIZE`])
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/// - item 2: free level 2 blocks (with size 4*[`BLOCK_SIZE`])
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/// ...and so on.
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///
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/// Each inner array contains a list of free block indices,
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levels: Vec<Vec<u64>>,
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}
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impl Allocator {
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pub fn levels(&self) -> &Vec<Vec<u64>> {
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&self.levels
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}
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/// Count the number of free [`BLOCK_SIZE`] available to this [`Allocator`].
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pub fn free(&self) -> u64 {
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let mut free = 0;
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for level in 0..self.levels.len() {
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let level_size = 1 << level;
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free += self.levels[level].len() as u64 * level_size;
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}
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free
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}
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/// Find a free block of the given level, mark it as "used", and return its address.
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/// Returns [`None`] if there are no free blocks with this level.
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pub fn allocate(&mut self, meta: BlockMeta) -> Option<BlockAddr> {
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// First, find the lowest level with a free block
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let mut index_opt = None;
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let mut level = meta.level.0;
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// Start searching at the level we want. Smaller levels are too small!
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while level < self.levels.len() {
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if !self.levels[level].is_empty() {
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index_opt = self.levels[level].pop();
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break;
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}
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level += 1;
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}
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// If a free block was found, split it until we find a usable block of the right level.
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// The left side of the split block is kept free, and the right side is allocated.
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let index = index_opt?;
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while level > meta.level.0 {
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level -= 1;
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let level_size = 1 << level;
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self.levels[level].push(index + level_size);
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}
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Some(unsafe { BlockAddr::new(index, meta) })
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}
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/// Try to allocate the exact block specified, making all necessary splits.
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/// Returns [`None`] if this some (or all) of this block is already allocated.
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///
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/// Note that [`BlockAddr`] encodes the blocks location _and_ level.
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pub fn allocate_exact(&mut self, exact_addr: BlockAddr) -> Option<BlockAddr> {
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// This function only supports level 0 right now
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assert_eq!(exact_addr.level().0, 0);
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let exact_index = exact_addr.index();
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let mut index_opt = None;
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// Go from the highest to the lowest level
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for level in (0..self.levels.len()).rev() {
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let level_size = 1 << level;
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// Split higher block if found
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if let Some(index) = index_opt.take() {
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self.levels[level].push(index);
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self.levels[level].push(index + level_size);
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}
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// Look for matching block and remove it
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for i in 0..self.levels[level].len() {
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let start = self.levels[level][i];
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if start <= exact_index {
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let end = start + level_size;
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if end > exact_index {
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self.levels[level].remove(i);
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index_opt = Some(start);
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break;
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}
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}
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}
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}
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Some(unsafe { BlockAddr::new(index_opt?, exact_addr.meta()) })
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}
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/// Deallocate the given block, marking it "free" so that it can be re-used later.
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pub fn deallocate(&mut self, addr: BlockAddr) {
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// When we deallocate, we check if block we're deallocating has a free sibling.
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// If it does, we join the two to create one free block in the next (higher) level.
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//
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// We repeat this until we no longer have a sibling to join.
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let mut index = addr.index();
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let mut level = addr.level().0;
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loop {
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while level >= self.levels.len() {
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self.levels.push(Vec::new());
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}
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let level_size = 1 << level;
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let next_size = level_size << 1;
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let mut found = false;
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let mut i = 0;
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// look at all free blocks in the current level...
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while i < self.levels[level].len() {
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// index of the second block we're looking at
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let level_index = self.levels[level][i];
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// - the block we just freed aligns with the next largest block, and
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// - the second block we're looking at is the right sibling of this block
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if index % next_size == 0 && index + level_size == level_index {
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// "alloc" the next highest block, repeat deallocation process.
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self.levels[level].remove(i);
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found = true;
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break;
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// - the index of this block doesn't align with the next largest block, and
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// - the block we're looking at is the left neighbor of this block
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} else if level_index % next_size == 0 && level_index + level_size == index {
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// "alloc" the next highest block, repeat deallocation process.
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self.levels[level].remove(i);
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index = level_index; // index moves to left block
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found = true;
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break;
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}
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i += 1;
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}
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// We couldn't find a higher block,
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// deallocate this one and finish
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if !found {
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self.levels[level].push(index);
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return;
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}
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// repeat deallocation process on the
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// higher-level block we just created.
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level += 1;
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}
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}
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}
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#[repr(C, packed)]
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#[derive(Clone, Copy, Default, Debug)]
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pub struct AllocEntry {
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/// The index of the first block this [`AllocEntry`] refers to
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index: Le<u64>,
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/// The number of blocks after (and including) `index` that are are free or used.
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/// If negative, they are used; if positive, they are free.
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count: Le<i64>,
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}
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impl AllocEntry {
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pub fn new(index: u64, count: i64) -> Self {
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Self {
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index: index.into(),
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count: count.into(),
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}
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}
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pub fn allocate(addr: BlockAddr) -> Self {
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Self::new(addr.index(), -addr.level().blocks::<i64>())
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}
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pub fn deallocate(addr: BlockAddr) -> Self {
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Self::new(addr.index(), addr.level().blocks::<i64>())
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}
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pub fn index(&self) -> u64 {
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self.index.to_ne()
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}
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pub fn count(&self) -> i64 {
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self.count.to_ne()
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}
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pub fn is_null(&self) -> bool {
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self.count() == 0
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}
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}
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/// A node in the allocation chain.
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#[repr(C, packed)]
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pub struct AllocList {
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/// A pointer to the previous AllocList.
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/// If this is the null pointer, this is the first element of the chain.
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pub prev: BlockPtr<AllocList>,
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/// Allocation entries.
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pub entries: [AllocEntry; ALLOC_LIST_ENTRIES],
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}
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unsafe impl BlockTrait for AllocList {
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fn empty(level: BlockLevel) -> Option<Self> {
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if level.0 == 0 {
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Some(Self {
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prev: BlockPtr::default(),
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entries: [AllocEntry::default(); ALLOC_LIST_ENTRIES],
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})
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} else {
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None
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}
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}
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}
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impl fmt::Debug for AllocList {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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let prev = self.prev;
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let entries: Vec<&AllocEntry> = self
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.entries
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.iter()
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.filter(|entry| entry.count() > 0)
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.collect();
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f.debug_struct("AllocList")
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.field("prev", &prev)
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.field("entries", &entries)
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.finish()
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}
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}
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impl ops::Deref for AllocList {
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type Target = [u8];
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fn deref(&self) -> &[u8] {
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unsafe {
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slice::from_raw_parts(
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self as *const AllocList as *const u8,
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mem::size_of::<AllocList>(),
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) as &[u8]
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}
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}
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}
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impl ops::DerefMut for AllocList {
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fn deref_mut(&mut self) -> &mut [u8] {
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unsafe {
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slice::from_raw_parts_mut(
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self as *mut AllocList as *mut u8,
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mem::size_of::<AllocList>(),
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) as &mut [u8]
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}
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}
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}
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#[test]
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fn alloc_node_size_test() {
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assert_eq!(mem::size_of::<AllocList>(), crate::BLOCK_SIZE as usize);
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}
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#[test]
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fn allocator_test() {
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let mut alloc = Allocator::default();
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assert_eq!(alloc.allocate(BlockMeta::default()), None);
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alloc.deallocate(unsafe { BlockAddr::new(1, BlockMeta::default()) });
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assert_eq!(
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alloc.allocate(BlockMeta::default()),
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Some(unsafe { BlockAddr::new(1, BlockMeta::default()) })
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);
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assert_eq!(alloc.allocate(BlockMeta::default()), None);
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for addr in 1023..2048 {
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alloc.deallocate(unsafe { BlockAddr::new(addr, BlockMeta::default()) });
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}
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assert_eq!(alloc.levels.len(), 11);
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for level in 0..alloc.levels.len() {
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if level == 0 {
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assert_eq!(alloc.levels[level], [1023]);
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} else if level == 10 {
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assert_eq!(alloc.levels[level], [1024]);
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} else {
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assert_eq!(alloc.levels[level], [0u64; 0]);
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}
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}
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for addr in 1023..2048 {
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assert_eq!(
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alloc.allocate(BlockMeta::default()),
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Some(unsafe { BlockAddr::new(addr, BlockMeta::default()) })
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);
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}
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assert_eq!(alloc.allocate(BlockMeta::default()), None);
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assert_eq!(alloc.levels.len(), 11);
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for level in 0..alloc.levels.len() {
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assert_eq!(alloc.levels[level], [0u64; 0]);
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}
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}
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