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feat: allow to reserve space in freelist

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This commit is contained in:
Paul Pan 2024-04-06 20:40:38 +08:00
parent bca4e37ef2
commit 2aa88154b4
1 changed files with 119 additions and 57 deletions
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176
kernel/src/vspace/allocator/freelist.rs
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@ -1,5 +1,6 @@
// adapted from https://os.phil-opp.com/allocator-designs/#linked-list-allocator
use crate::utils::then::Then;
use crate::vspace::addr::{AddressOps, PhysAddr};
use core::alloc::{GlobalAlloc, Layout};
use spin::Mutex;
@ -21,6 +22,24 @@ impl ListNode {
fn end_addr(&self) -> PhysAddr {
self.start_addr() + self.size
}
fn fit(&self, size: usize, align: usize) -> Result<PhysAddr, ()> {
let alloc_start = self.start_addr().align_up(align);
let alloc_end = alloc_start + size;
if alloc_end > self.end_addr() {
return Err(());
}
let excess_size = (self.end_addr() - alloc_end).as_usize();
if excess_size > 0 && excess_size < core::mem::size_of::<ListNode>() {
// GlobalAlloc requires that dealloc be called with the original size and alignment,
// so we can't "waste" the remaining space and must return an error.
return Err(());
}
Ok(alloc_start)
}
}
struct FreeList {
@ -34,7 +53,47 @@ impl FreeList {
}
}
unsafe fn add_free_region(&mut self, start: PhysAddr, size: usize) {
fn alloc_node<F, V>(&mut self, mut predicate: F) -> Option<(&'static mut ListNode, V)>
where F: FnMut(&mut ListNode) -> Result<V, ()> {
let mut current = &mut self.head;
while let Some(ref mut region) = current.next {
if let Ok(v) = predicate(region) {
let next = region.next.take();
let ret = Some((current.next.take().unwrap(), v));
current.next = next;
return ret;
} else {
current = current.next.as_mut().unwrap();
}
}
None
}
fn align_layout(layout: Layout) -> (usize, usize) {
let layout = layout
.align_to(core::mem::align_of::<ListNode>())
.expect("adjusting alignment failed")
.pad_to_align();
let size = layout.size().max(core::mem::size_of::<ListNode>());
(size, layout.align())
}
unsafe fn alloc(&mut self, layout: Layout) -> *mut u8 {
let (size, align) = Self::align_layout(layout);
if let Some((region, alloc_start)) = self.alloc_node(|region| region.fit(size, align)) {
let alloc_end = alloc_start + size;
let excess_size = (region.end_addr() - alloc_end).as_usize();
if excess_size > 0 {
self.dealloc(alloc_end, excess_size);
}
alloc_start.as_mut_ptr()
} else {
core::ptr::null_mut()
}
}
unsafe fn dealloc(&mut self, start: PhysAddr, size: usize) {
assert_eq!(start.align_up(core::mem::align_of::<ListNode>()), start);
assert!(size >= core::mem::size_of::<ListNode>());
@ -45,39 +104,31 @@ impl FreeList {
self.head.next = Some(&mut *node_ptr);
}
fn find_region(
&mut self,
size: usize,
align: usize,
) -> Option<(&'static mut ListNode, PhysAddr)> {
let mut current = &mut self.head;
while let Some(ref mut region) = current.next {
if let Ok(alloc_start) = Self::alloc_from_region(&region, size, align) {
let next = region.next.take();
let ret = Some((current.next.take().unwrap(), alloc_start));
current.next = next;
return ret;
} else {
current = current.next.as_mut().unwrap();
pub fn reserve(&mut self, start: PhysAddr, size: usize) {
if let Some((region, _)) = self
.alloc_node(|region| (region.start_addr() <= start).chain(|| region.fit(size, 1), ()))
{
/* layout
* region: | before | [start +: size] | after |
* ^ ^ ^ ^ region.end_addr()
* | | alloc_start |
* | | alloc_end
* | region.start_addr()
*/
let region_start = region.start_addr();
let region_end = region.end_addr();
let before_size = (start - region_start).as_usize();
if before_size > 0 {
unsafe { self.dealloc(region_start, before_size) }
}
let after_size = (region_end - (start + size)).as_usize();
if after_size > 0 {
unsafe { self.dealloc(start + size, after_size) }
}
}
None
}
fn alloc_from_region(region: &ListNode, size: usize, align: usize) -> Result<PhysAddr, ()> {
let alloc_start = region.start_addr().align_up(align);
let alloc_end = alloc_start + size;
if alloc_end > region.end_addr() {
return Err(());
}
let excess_size = (region.end_addr() - alloc_end).as_usize();
if excess_size > 0 && excess_size < core::mem::size_of::<ListNode>() {
return Err(());
}
Ok(alloc_start)
}
}
@ -88,42 +139,21 @@ pub struct FreeListAllocator {
impl FreeListAllocator {
pub fn new(start: PhysAddr, size: usize) -> Self {
let mut list = FreeList::new();
unsafe { list.add_free_region(start, size) }
unsafe { list.dealloc(start, size) }
Self {
list: Mutex::new(list),
}
}
fn size_align(layout: Layout) -> (usize, usize) {
let layout = layout
.align_to(core::mem::align_of::<ListNode>())
.expect("adjusting alignment failed")
.pad_to_align();
let size = layout.size().max(core::mem::size_of::<ListNode>());
(size, layout.align())
}
}
unsafe impl GlobalAlloc for FreeListAllocator {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
let (size, align) = Self::size_align(layout);
let mut allocator = self.list.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).as_usize();
if excess_size > 0 {
allocator.add_free_region(alloc_end, excess_size);
}
alloc_start.as_mut_ptr()
} else {
core::ptr::null_mut()
}
self.list.lock().alloc(layout)
}
unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
let (size, _) = Self::size_align(layout);
self.list.lock().add_free_region(PhysAddr::from(ptr), size)
let (size, _) = FreeList::align_layout(layout);
self.list.lock().dealloc(PhysAddr::from(ptr), size)
}
}
@ -158,4 +188,36 @@ mod tests {
unsafe { allocator.alloc(Layout::from_size_align(PAGE_SIZE, PAGE_SIZE).unwrap()) };
assert_eq!(ptr as usize, BASE.as_usize());
}
#[test_case]
fn test_freelist_reserve() {
const BASE: PhysAddr = PhysAddr(0x80300000);
let allocator = FreeListAllocator::new(BASE, 32 * PAGE_SIZE);
allocator
.list
.lock()
.reserve(BASE + 4 * PAGE_SIZE, 4 * PAGE_SIZE);
let mut cnt = 32 - 4;
loop {
let ptr =
unsafe { allocator.alloc(Layout::from_size_align(PAGE_SIZE, PAGE_SIZE).unwrap()) };
if ptr.is_null() {
assert_eq!(cnt, 0);
break;
}
let ptr = PhysAddr::from(ptr);
assert!(
!(BASE + 4 * PAGE_SIZE <= ptr && ptr < BASE + (4 + 4) * PAGE_SIZE),
"Bad alloc: returned ptr: {:?}, reserved range: {:?}->{:?}",
ptr,
BASE + 4 * PAGE_SIZE,
BASE + (4 + 4) * PAGE_SIZE
);
cnt -= 1;
}
}
}