mmtk/policy/marksweepspace/native_ms/
block.rs

1// adapted from Immix
2
3use atomic::Ordering;
4
5use super::BlockList;
6use super::MarkSweepSpace;
7use crate::util::constants::LOG_BYTES_IN_PAGE;
8use crate::util::heap::chunk_map::*;
9use crate::util::linear_scan::Region;
10use crate::util::linear_scan::UnstraddlableRegion;
11use crate::util::object_enum::BlockMayHaveObjects;
12use crate::vm::ObjectModel;
13use crate::{
14    util::{
15        metadata::side_metadata::SideMetadataSpec, Address, ObjectReference, OpaquePointer,
16        VMThread,
17    },
18    vm::VMBinding,
19};
20
21use std::num::NonZeroUsize;
22
23/// A 64KB region for MiMalloc.
24/// This is also known as MiMalloc page. We try to avoid getting confused with the OS 4K page. So we call it block.
25/// This type always holds a non-zero address to refer to a block. The underlying `NonZeroUsize` type ensures the
26/// size of `Option<Block>` is the same as `Block` itself.
27// TODO: If we actually use the first block, we would need to turn the type into `Block(Address)`, and use `None` and
28// `Block(Address::ZERO)` to differentiate those.
29#[derive(Clone, Copy, PartialOrd, PartialEq)]
30#[repr(transparent)]
31pub struct Block(NonZeroUsize);
32
33impl std::fmt::Debug for Block {
34    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
35        write!(f, "Block(0x{:x})", self.0)
36    }
37}
38
39impl Region for Block {
40    const LOG_BYTES: usize = 16;
41
42    fn from_aligned_address(address: Address) -> Self {
43        debug_assert!(address.is_aligned_to(Self::BYTES));
44        debug_assert!(!address.is_zero());
45        Self(unsafe { NonZeroUsize::new_unchecked(address.as_usize()) })
46    }
47
48    fn start(&self) -> Address {
49        unsafe { Address::from_usize(self.0.get()) }
50    }
51}
52
53/// An objects cannot straddle multiple native  blocks.
54impl UnstraddlableRegion for Block {}
55
56impl BlockMayHaveObjects for Block {
57    fn may_have_objects(&self) -> bool {
58        self.get_state() != BlockState::Unallocated
59    }
60}
61
62impl Block {
63    /// Log pages in block
64    pub const LOG_PAGES: usize = Self::LOG_BYTES - LOG_BYTES_IN_PAGE as usize;
65
66    pub const METADATA_SPECS: [SideMetadataSpec; 7] = [
67        Self::MARK_TABLE,
68        Self::NEXT_BLOCK_TABLE,
69        Self::PREV_BLOCK_TABLE,
70        Self::FREE_LIST_TABLE,
71        Self::SIZE_TABLE,
72        Self::BLOCK_LIST_TABLE,
73        Self::TLS_TABLE,
74    ];
75
76    /// Block mark table (side)
77    pub const MARK_TABLE: SideMetadataSpec =
78        crate::util::metadata::side_metadata::spec_defs::MS_BLOCK_MARK;
79
80    pub const NEXT_BLOCK_TABLE: SideMetadataSpec =
81        crate::util::metadata::side_metadata::spec_defs::MS_BLOCK_NEXT;
82
83    pub const PREV_BLOCK_TABLE: SideMetadataSpec =
84        crate::util::metadata::side_metadata::spec_defs::MS_BLOCK_PREV;
85
86    pub const FREE_LIST_TABLE: SideMetadataSpec =
87        crate::util::metadata::side_metadata::spec_defs::MS_FREE;
88
89    // needed for non GC context
90    #[cfg(feature = "malloc_native_mimalloc")]
91    pub const LOCAL_FREE_LIST_TABLE: SideMetadataSpec =
92        crate::util::metadata::side_metadata::spec_defs::MS_LOCAL_FREE;
93
94    #[cfg(feature = "malloc_native_mimalloc")]
95    pub const THREAD_FREE_LIST_TABLE: SideMetadataSpec =
96        crate::util::metadata::side_metadata::spec_defs::MS_THREAD_FREE;
97
98    pub const SIZE_TABLE: SideMetadataSpec =
99        crate::util::metadata::side_metadata::spec_defs::MS_BLOCK_SIZE;
100
101    pub const BLOCK_LIST_TABLE: SideMetadataSpec =
102        crate::util::metadata::side_metadata::spec_defs::MS_BLOCK_LIST;
103
104    pub const TLS_TABLE: SideMetadataSpec =
105        crate::util::metadata::side_metadata::spec_defs::MS_BLOCK_TLS;
106
107    pub fn load_free_list(&self) -> Address {
108        unsafe { Address::from_usize(Block::FREE_LIST_TABLE.load::<usize>(self.start())) }
109    }
110
111    pub fn store_free_list(&self, free_list: Address) {
112        unsafe { Block::FREE_LIST_TABLE.store::<usize>(self.start(), free_list.as_usize()) }
113    }
114
115    #[cfg(feature = "malloc_native_mimalloc")]
116    pub fn load_local_free_list(&self) -> Address {
117        unsafe { Address::from_usize(Block::LOCAL_FREE_LIST_TABLE.load::<usize>(self.start())) }
118    }
119
120    #[cfg(feature = "malloc_native_mimalloc")]
121    pub fn store_local_free_list(&self, local_free: Address) {
122        unsafe { Block::LOCAL_FREE_LIST_TABLE.store::<usize>(self.start(), local_free.as_usize()) }
123    }
124
125    #[cfg(feature = "malloc_native_mimalloc")]
126    pub fn load_thread_free_list(&self) -> Address {
127        unsafe {
128            Address::from_usize(
129                Block::THREAD_FREE_LIST_TABLE.load_atomic::<usize>(self.start(), Ordering::SeqCst),
130            )
131        }
132    }
133
134    #[cfg(feature = "malloc_native_mimalloc")]
135    pub fn store_thread_free_list(&self, thread_free: Address) {
136        unsafe {
137            Block::THREAD_FREE_LIST_TABLE.store::<usize>(self.start(), thread_free.as_usize())
138        }
139    }
140
141    #[cfg(feature = "malloc_native_mimalloc")]
142    pub fn cas_thread_free_list(&self, old_thread_free: Address, new_thread_free: Address) -> bool {
143        Block::THREAD_FREE_LIST_TABLE
144            .compare_exchange_atomic::<usize>(
145                self.start(),
146                old_thread_free.as_usize(),
147                new_thread_free.as_usize(),
148                Ordering::SeqCst,
149                Ordering::SeqCst,
150            )
151            .is_ok()
152    }
153
154    pub fn load_prev_block(&self) -> Option<Block> {
155        let prev = unsafe { Block::PREV_BLOCK_TABLE.load::<usize>(self.start()) };
156        NonZeroUsize::new(prev).map(Block)
157    }
158
159    pub fn load_next_block(&self) -> Option<Block> {
160        let next = unsafe { Block::NEXT_BLOCK_TABLE.load::<usize>(self.start()) };
161        NonZeroUsize::new(next).map(Block)
162    }
163
164    pub fn store_next_block(&self, next: Block) {
165        unsafe {
166            Block::NEXT_BLOCK_TABLE.store::<usize>(self.start(), next.start().as_usize());
167        }
168    }
169
170    pub fn clear_next_block(&self) {
171        unsafe {
172            Block::NEXT_BLOCK_TABLE.store::<usize>(self.start(), 0);
173        }
174    }
175
176    pub fn store_prev_block(&self, prev: Block) {
177        unsafe {
178            Block::PREV_BLOCK_TABLE.store::<usize>(self.start(), prev.start().as_usize());
179        }
180    }
181
182    pub fn clear_prev_block(&self) {
183        unsafe {
184            Block::PREV_BLOCK_TABLE.store::<usize>(self.start(), 0);
185        }
186    }
187
188    pub fn store_block_list(&self, block_list: &BlockList) {
189        let block_list_usize: usize = block_list as *const BlockList as usize;
190        unsafe {
191            Block::BLOCK_LIST_TABLE.store::<usize>(self.start(), block_list_usize);
192        }
193    }
194
195    pub fn load_block_list(&self) -> *mut BlockList {
196        let block_list =
197            Block::BLOCK_LIST_TABLE.load_atomic::<usize>(self.start(), Ordering::SeqCst);
198        block_list as *mut BlockList
199    }
200
201    pub fn load_block_cell_size(&self) -> usize {
202        Block::SIZE_TABLE.load_atomic::<usize>(self.start(), Ordering::SeqCst)
203    }
204
205    pub fn store_block_cell_size(&self, size: usize) {
206        debug_assert_ne!(size, 0);
207        unsafe { Block::SIZE_TABLE.store::<usize>(self.start(), size) }
208    }
209
210    pub fn store_tls(&self, tls: VMThread) {
211        let tls_usize: usize = tls.0.to_address().as_usize();
212        unsafe { Block::TLS_TABLE.store(self.start(), tls_usize) }
213    }
214
215    pub fn load_tls(&self) -> VMThread {
216        let tls = Block::TLS_TABLE.load_atomic::<usize>(self.start(), Ordering::SeqCst);
217        VMThread(OpaquePointer::from_address(unsafe {
218            Address::from_usize(tls)
219        }))
220    }
221
222    pub fn has_free_cells(&self) -> bool {
223        !self.load_free_list().is_zero()
224    }
225
226    /// Get block mark state.
227    pub fn get_state(&self) -> BlockState {
228        let byte = Self::MARK_TABLE.load_atomic::<u8>(self.start(), Ordering::SeqCst);
229        byte.into()
230    }
231
232    /// Set block mark state.
233    pub fn set_state(&self, state: BlockState) {
234        let state = u8::from(state);
235        Self::MARK_TABLE.store_atomic::<u8>(self.start(), state, Ordering::SeqCst);
236    }
237
238    /// Release this block if it is unmarked. Return true if the block is released.
239    pub fn attempt_release<VM: VMBinding>(self, space: &MarkSweepSpace<VM>) -> bool {
240        match self.get_state() {
241            // We should not have unallocated blocks in a block list
242            BlockState::Unallocated => unreachable!(),
243            BlockState::Unmarked => {
244                let block_list = self.load_block_list();
245                unsafe { &mut *block_list }.remove(self);
246                space.release_block(self);
247                true
248            }
249            BlockState::Marked => {
250                // The block is live.
251                false
252            }
253        }
254    }
255
256    /// Sweep the block. This is done either lazily in the allocation phase, or eagerly at the end of a GC.
257    pub fn sweep<VM: VMBinding>(&self) {
258        // The important point here is that we need to distinguish cell address, allocation address, and object reference.
259        // We only know cell addresses here. We do not know the allocation address, and we also do not know the object reference.
260        // The mark bit is set for object references, and we need to use the mark bit to decide whether a cell is live or not.
261
262        // We haven't implemented for malloc/free cases, for which we do not have mark bit. We could use valid object bit instead.
263        if cfg!(feature = "malloc_native_mimalloc") {
264            unimplemented!()
265        }
266
267        // Check if we can treat it as the simple case: cell address === object reference.
268        // If the binding does not use allocation offset, and they use the same allocation alignment which the cell size is aligned to,
269        // then we have cell address === allocation address.
270        // Furthermore, if the binding does not have an offset between allocation and object reference, then allocation address === cell address.
271        if !VM::USE_ALLOCATION_OFFSET
272            && VM::MAX_ALIGNMENT == VM::MIN_ALIGNMENT
273            && crate::util::conversions::raw_is_aligned(
274                self.load_block_cell_size(),
275                VM::MAX_ALIGNMENT,
276            )
277            && VM::VMObjectModel::UNIFIED_OBJECT_REFERENCE_ADDRESS
278        {
279            // In this case, we can use the simplest and the most efficicent sweep.
280            self.simple_sweep::<VM>()
281        } else {
282            // Otherwise we fallback to a generic but slow sweep. This roughly has ~10% mutator overhead for lazy sweeping.
283            self.naive_brute_force_sweep::<VM>()
284        }
285    }
286
287    /// This implementation uses object reference and cell address interchangably. This is not correct for most cases.
288    /// However, in certain cases, such as OpenJDK, this is correct, and efficient. See the sweep method for the invariants
289    /// that we need to use this method correctly.
290    fn simple_sweep<VM: VMBinding>(&self) {
291        let cell_size = self.load_block_cell_size();
292        debug_assert_ne!(cell_size, 0);
293        let mut cell = self.start();
294        let mut last = unsafe { Address::zero() };
295        while cell + cell_size <= self.start() + Block::BYTES {
296            // The invariants we checked earlier ensures that we can use cell and object reference interchangably
297            // We may not really have an object in this cell, but if we do, this object reference is correct.
298            // About unsafe: We know `cell` is non-zero here.
299            let potential_object = unsafe { ObjectReference::from_raw_address_unchecked(cell) };
300
301            if !VM::VMObjectModel::LOCAL_MARK_BIT_SPEC
302                .is_marked::<VM>(potential_object, Ordering::SeqCst)
303            {
304                // clear VO bit if it is ever set. It is possible that the VO bit is never set for this cell (i.e. there was no object in this cell before this GC),
305                // we unset the bit anyway.
306                #[cfg(feature = "vo_bit")]
307                crate::util::metadata::vo_bit::unset_vo_bit_nocheck(potential_object);
308                unsafe {
309                    cell.store::<Address>(last);
310                }
311                last = cell;
312            }
313            cell += cell_size;
314        }
315
316        self.store_free_list(last);
317    }
318
319    /// This is a naive implementation that is inefficient but should be correct.
320    /// In this implementation, we simply go through each possible object
321    /// reference and see if it has the mark bit set. If we find mark bit, that means the cell is alive. If we didn't find
322    /// the mark bit in the entire cell, it means the cell is dead.
323    fn naive_brute_force_sweep<VM: VMBinding>(&self) {
324        use crate::util::constants::MIN_OBJECT_SIZE;
325
326        // Cell size for this block.
327        let cell_size = self.load_block_cell_size();
328        // Current cell
329        let mut cell = self.start();
330        // Last free cell in the free list
331        let mut last = Address::ZERO;
332        // Current cursor
333        let mut cursor = cell;
334
335        debug!("Sweep block {:?}, cell size {}", self, cell_size);
336
337        while cell + cell_size <= self.end() {
338            // possible object ref
339            let potential_object_ref = unsafe {
340                // We know cursor plus an offset cannot be 0.
341                ObjectReference::from_raw_address_unchecked(
342                    cursor + VM::VMObjectModel::OBJECT_REF_OFFSET_LOWER_BOUND,
343                )
344            };
345            trace!(
346                "{:?}: cell = {}, last cell in free list = {}, cursor = {}, potential object = {}",
347                self,
348                cell,
349                last,
350                cursor,
351                potential_object_ref
352            );
353
354            if VM::VMObjectModel::LOCAL_MARK_BIT_SPEC
355                .is_marked::<VM>(potential_object_ref, Ordering::SeqCst)
356            {
357                debug!("{:?} Live cell: {}", self, cell);
358                // If the mark bit is set, the cell is alive.
359                // We directly jump to the end of the cell.
360                cell += cell_size;
361                cursor = cell;
362            } else {
363                // If the mark bit is not set, we don't know if the cell is alive or not. We keep search for the mark bit.
364                cursor += MIN_OBJECT_SIZE;
365
366                if cursor >= cell + cell_size {
367                    // We now stepped to the next cell. This means we did not find mark bit in the current cell, and we can add this cell to free list.
368                    debug!(
369                        "{:?} Free cell: {}, last cell in freelist is {}",
370                        self, cell, last
371                    );
372
373                    // Clear VO bit: we don't know where the object reference actually is, so we bulk zero the cell.
374                    #[cfg(feature = "vo_bit")]
375                    crate::util::metadata::vo_bit::bzero_vo_bit(cell, cell_size);
376
377                    // store the previous cell to make the free list
378                    debug_assert!(last.is_zero() || (last >= self.start() && last < self.end()));
379                    unsafe {
380                        cell.store::<Address>(last);
381                    }
382                    last = cell;
383                    cell += cell_size;
384                    debug_assert_eq!(cursor, cell);
385                }
386            }
387        }
388
389        self.store_free_list(last);
390    }
391
392    /// Get the chunk containing the block.
393    pub fn chunk(&self) -> Chunk {
394        Chunk::from_unaligned_address(self.start())
395    }
396
397    /// Initialize a clean block after acquired from page-resource.
398    pub fn init(&self) {
399        self.set_state(BlockState::Unmarked);
400    }
401
402    /// Deinitalize a block before releasing.
403    pub fn deinit(&self) {
404        self.set_state(BlockState::Unallocated);
405    }
406}
407
408/// The block allocation state.
409#[derive(Debug, PartialEq, Clone, Copy)]
410pub enum BlockState {
411    /// the block is not allocated.
412    Unallocated,
413    /// the block is allocated but not marked.
414    Unmarked,
415    /// the block is allocated and marked.
416    Marked,
417}
418
419impl BlockState {
420    /// Private constant
421    const MARK_UNALLOCATED: u8 = 0;
422    /// Private constant
423    const MARK_UNMARKED: u8 = u8::MAX;
424    /// Private constant
425    const MARK_MARKED: u8 = u8::MAX - 1;
426}
427
428impl From<u8> for BlockState {
429    fn from(state: u8) -> Self {
430        match state {
431            Self::MARK_UNALLOCATED => BlockState::Unallocated,
432            Self::MARK_UNMARKED => BlockState::Unmarked,
433            Self::MARK_MARKED => BlockState::Marked,
434            _ => unreachable!(),
435        }
436    }
437}
438
439impl From<BlockState> for u8 {
440    fn from(state: BlockState) -> Self {
441        match state {
442            BlockState::Unallocated => BlockState::MARK_UNALLOCATED,
443            BlockState::Unmarked => BlockState::MARK_UNMARKED,
444            BlockState::Marked => BlockState::MARK_MARKED,
445        }
446    }
447}
mmtk/policy/marksweepspace/native_ms/block.rs

mmtk/policy/marksweepspace/native_ms/
block.rs
