rustubs/mm/
pma.rs

1//! (deprecated) a simple stack based 4K physical frame allocator.
2//!
3//! Adcantages
4//! 1. allocation and deallocation is O(1).
5//! 2. can manage fragmented (non-consecutive) memory regions and doesn't suffer
6//!    fragmentation because memory is fully virtualized.
7//!
8//! Limitations
9//! 1. slow initialization: needs to traverse all available pages and push their
10//!    address one by one
11//! 2. can't give continous physical memory of more than 4K
12//! 3. the allocator stack itself requires continous space (it's an array), and
13//!    has a higher storage overhead: every page requires 8 bytes for the
14//!    address, that's `8/4096 == 1/512`.
15//! 4. (kinda?) conflicts kmalloc/vmalloc design in e.g. linux kernel, kmalloc
16//!    manages the __identically mapped__ virtual memory in the kernel address
17//!    space, that is `0xffff800000000000 + 64G` in rustubs, in another word,
18//!    the kmalloc manages the physical memory: obviously this one only gives 4K
19//!    memory and can't work as a kmalloc backend!
20
21use crate::defs::*;
22use core::ops::Range;
23use core::slice;
24// disabled for now
25// lazy_static! {
26// 	pub static ref GLOBAL_PMA: Mutex<pma::PageStackAllocator> =
27// 		Mutex::new(pma::PageStackAllocator::new());
28// }
29
30/// There should only be one global instance of this.
31pub struct PageStackAllocator {
32	page_stack: &'static mut [u64],
33	size: usize,
34	head: usize,
35}
36
37#[allow(dead_code)]
38impl PageStackAllocator {
39	// covering 4GiB physical memory of 4K frames
40	const STACK_SIZE: usize = 0x100000;
41
42	pub fn new() -> Self {
43		let ps = Self {
44			page_stack: unsafe {
45				slice::from_raw_parts_mut(
46					P2V(ExternSyms::___FREE_PAGE_STACK__ as u64).unwrap()
47						as *mut u64,
48					Self::STACK_SIZE,
49				)
50			},
51			size: Self::STACK_SIZE,
52			head: 0,
53		};
54		return ps;
55	}
56
57	/// push an addr into the free page stack
58	/// MUST be atomic or bad things happen...
59	pub fn free_page(&mut self, addr: u64) -> bool {
60		if self.head >= self.size {
61			return false;
62		}
63		self.page_stack[self.head] = addr;
64		self.head += 1;
65		return true;
66	}
67
68	pub fn alloc_page(&mut self) -> Option<u64> {
69		if self.head == 0 {
70			return None;
71		}
72		self.head -= 1;
73		Some(self.page_stack[self.head])
74	}
75
76	/// 4k page only?
77	pub fn insert_range(&mut self, r: &Range<u64>) -> u64 {
78		// r.contains(&1);
79		let mut inserted = 0;
80		let mut page = roundup_4k(r.start);
81		loop {
82			if !r.contains(&page) {
83				break;
84			}
85			if !self.free_page(page) {
86				break;
87			} else {
88				inserted += 1;
89			}
90			page += 0x1000;
91		}
92		return inserted;
93	}
94}
rustubs/mm/pma.rs

rustubs/mm/
pma.rs
