Implement AllocatorInfo (#889)

This type adds `AllocatorInfo` enum that can be used to query offset of
allocator fields for fast-path generation. Currently all bindings have
to re-declare `*Allocator` types with the same layout as in mmtk-core in
order to get offset of these fields. This enum simplifies that, all you
need to do is invoke `get_allocator_info(selector)`.

Cargo.toml

@@ -36,6 +36,7 @@ jemalloc-sys = { version = "0.5.3", features = ["disable_initial_exec_tls"], opt
 lazy_static = "1.1"
 libc = "0.2"
 log = { version = "0.4", features = ["max_level_trace", "release_max_level_off"] }
+memoffset = "0.9"
 mimalloc-sys = { version = "0.1.6", optional = true }
 # MMTk macros
 mmtk-macros = { version = "0.18.0", path = "macros/" }

src/memory_manager.rs

@@ -27,7 +27,6 @@ use crate::vm::edge_shape::MemorySlice;
 use crate::vm::ReferenceGlue;
 use crate::vm::VMBinding;
 use std::sync::atomic::Ordering;
-
 /// Initialize an MMTk instance. A VM should call this method after creating an [`crate::MMTK`]
 /// instance but before using any of the methods provided in MMTk (except `process()` and `process_bulk()`).
 ///

src/util/alloc/allocators.rs

@@ -1,5 +1,8 @@
+use std::mem::size_of;
 use std::mem::MaybeUninit;
 
+use memoffset::offset_of;
+
 use crate::plan::Plan;
 use crate::policy::largeobjectspace::LargeObjectSpace;
 use crate::policy::marksweepspace::malloc_ms::MallocSpace;
@@ -10,6 +13,7 @@ use crate::util::alloc::MallocAllocator;
 use crate::util::alloc::{Allocator, BumpAllocator, ImmixAllocator};
 use crate::util::VMMutatorThread;
 use crate::vm::VMBinding;
+use crate::Mutator;
 
 use super::FreeListAllocator;
 use super::MarkCompactAllocator;
@@ -175,3 +179,69 @@ impl Default for AllocatorSelector {
         AllocatorSelector::None
     }
 }
+
+/// This type describes allocator information. It is used to
+/// generate fast paths for the GC. All offset fields are relative to [`Mutator`](crate::Mutator).
+#[repr(C, u8)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub enum AllocatorInfo {
+    BumpPointer { bump_pointer_offset: usize },
+    // FIXME: Add free-list fast-path
+    Unimplemented,
+    None,
+}
+
+impl Default for AllocatorInfo {
+    fn default() -> Self {
+        AllocatorInfo::None
+    }
+}
+
+impl AllocatorInfo {
+    /// Return an AllocatorInfo for the given allocator selector. This method is provided
+    /// so that VM compilers may generate allocator fast-path and load fields for the fast-path.
+    ///
+    /// Arguments:
+    /// * `selector`: The allocator selector to query.
+    pub fn new<VM: VMBinding>(selector: AllocatorSelector) -> AllocatorInfo {
+        match selector {
+            AllocatorSelector::BumpPointer(index) => {
+                let base_offset = offset_of!(Mutator<VM>, allocators)
+                    + offset_of!(Allocators<VM>, bump_pointer)
+                    + size_of::<BumpAllocator<VM>>() * index as usize;
+                let bump_pointer_offset = offset_of!(BumpAllocator<VM>, bump_pointer);
+
+                AllocatorInfo::BumpPointer {
+                    bump_pointer_offset: base_offset + bump_pointer_offset,
+                }
+            }
+
+            AllocatorSelector::Immix(index) => {
+                let base_offset = offset_of!(Mutator<VM>, allocators)
+                    + offset_of!(Allocators<VM>, immix)
+                    + size_of::<ImmixAllocator<VM>>() * index as usize;
+                let bump_pointer_offset = offset_of!(ImmixAllocator<VM>, bump_pointer);
+
+                AllocatorInfo::BumpPointer {
+                    bump_pointer_offset: base_offset + bump_pointer_offset,
+                }
+            }
+
+            AllocatorSelector::MarkCompact(index) => {
+                let base_offset = offset_of!(Mutator<VM>, allocators)
+                    + offset_of!(Allocators<VM>, markcompact)
+                    + size_of::<MarkCompactAllocator<VM>>() * index as usize;
+                let bump_offset =
+                    base_offset + offset_of!(MarkCompactAllocator<VM>, bump_allocator);
+                let bump_pointer_offset = offset_of!(BumpAllocator<VM>, bump_pointer);
+
+                AllocatorInfo::BumpPointer {
+                    bump_pointer_offset: bump_offset + bump_pointer_offset,
+                }
+            }
+
+            AllocatorSelector::FreeList(_) => AllocatorInfo::Unimplemented,
+            _ => AllocatorInfo::None,
+        }
+    }
+}

src/util/alloc/bumpallocator.rs

@@ -1,4 +1,3 @@
-use super::allocator::{align_allocation_no_fill, fill_alignment_gap};
 use crate::util::Address;
 
 use crate::util::alloc::Allocator;
@@ -17,25 +16,44 @@ const BLOCK_MASK: usize = BLOCK_SIZE - 1;
 pub struct BumpAllocator<VM: VMBinding> {
     /// [`VMThread`] associated with this allocator instance
     pub tls: VMThread,
-    /// Current cursor for bump pointer
-    cursor: Address,
-    /// Limit for bump pointer
-    limit: Address,
+    /// Bump-pointer itself.
+    pub(in crate::util::alloc) bump_pointer: BumpPointer,
     /// [`Space`](src/policy/space/Space) instance associated with this allocator instance.
     space: &'static dyn Space<VM>,
     /// [`Plan`] instance that this allocator instance is associated with.
     plan: &'static dyn Plan<VM = VM>,
 }
 
+/// A common fast-path bump-pointer allocator shared across different allocator implementations
+/// that use bump-pointer allocation.
+#[repr(C)]
+pub struct BumpPointer {
+    pub cursor: Address,
+    pub limit: Address,
+}
+
+impl BumpPointer {
+    pub const fn new(start: Address, end: Address) -> Self {
+        BumpPointer {
+            cursor: start,
+            limit: end,
+        }
+    }
+
+    pub fn reset(&mut self, start: Address, end: Address) {
+        self.cursor = start;
+        self.limit = end;
+    }
+}
+
 impl<VM: VMBinding> BumpAllocator<VM> {
     pub fn set_limit(&mut self, start: Address, limit: Address) {
-        self.cursor = start;
-        self.limit = limit;
+        self.bump_pointer.reset(start, limit);
     }
 
     pub fn reset(&mut self) {
-        self.cursor = unsafe { Address::zero() };
-        self.limit = unsafe { Address::zero() };
+        let zero = unsafe { Address::zero() };
+        self.bump_pointer.reset(zero, zero);
     }
 
     pub fn rebind(&mut self, space: &'static dyn Space<VM>) {
@@ -44,6 +62,9 @@ impl<VM: VMBinding> BumpAllocator<VM> {
     }
 }
 
+use crate::util::alloc::allocator::align_allocation_no_fill;
+use crate::util::alloc::fill_alignment_gap;
+
 impl<VM: VMBinding> Allocator<VM> for BumpAllocator<VM> {
     fn get_space(&self) -> &'static dyn Space<VM> {
         self.space
@@ -63,21 +84,21 @@ impl<VM: VMBinding> Allocator<VM> for BumpAllocator<VM> {
 
     fn alloc(&mut self, size: usize, align: usize, offset: usize) -> Address {
         trace!("alloc");
-        let result = align_allocation_no_fill::<VM>(self.cursor, align, offset);
+        let result = align_allocation_no_fill::<VM>(self.bump_pointer.cursor, align, offset);
         let new_cursor = result + size;
 
-        if new_cursor > self.limit {
+        if new_cursor > self.bump_pointer.limit {
             trace!("Thread local buffer used up, go to alloc slow path");
             self.alloc_slow(size, align, offset)
         } else {
-            fill_alignment_gap::<VM>(self.cursor, result);
-            self.cursor = new_cursor;
+            fill_alignment_gap::<VM>(self.bump_pointer.cursor, result);
+            self.bump_pointer.cursor = new_cursor;
             trace!(
                 "Bump allocation size: {}, result: {}, new_cursor: {}, limit: {}",
                 size,
                 result,
-                self.cursor,
-                self.limit
+                self.bump_pointer.cursor,
+                self.bump_pointer.limit
             );
             result
         }
@@ -108,24 +129,24 @@ impl<VM: VMBinding> Allocator<VM> for BumpAllocator<VM> {
         }
 
         trace!("alloc_slow stress_test");
-        let result = align_allocation_no_fill::<VM>(self.cursor, align, offset);
+        let result = align_allocation_no_fill::<VM>(self.bump_pointer.cursor, align, offset);
         let new_cursor = result + size;
 
         // For stress test, limit is [0, block_size) to artificially make the
         // check in the fastpath (alloc()) fail. The real limit is recovered by
         // adding it to the current cursor.
-        if new_cursor > self.cursor + self.limit.as_usize() {
+        if new_cursor > self.bump_pointer.cursor + self.bump_pointer.limit.as_usize() {
             self.acquire_block(size, align, offset, true)
         } else {
-            fill_alignment_gap::<VM>(self.cursor, result);
-            self.limit -= new_cursor - self.cursor;
-            self.cursor = new_cursor;
+            fill_alignment_gap::<VM>(self.bump_pointer.cursor, result);
+            self.bump_pointer.limit -= new_cursor - self.bump_pointer.cursor;
+            self.bump_pointer.cursor = new_cursor;
             trace!(
                 "alloc_slow: Bump allocation size: {}, result: {}, new_cursor: {}, limit: {}",
                 size,
                 result,
-                self.cursor,
-                self.limit
+                self.bump_pointer.cursor,
+                self.bump_pointer.limit
             );
             result
         }
@@ -144,8 +165,7 @@ impl<VM: VMBinding> BumpAllocator<VM> {
     ) -> Self {
         BumpAllocator {
             tls,
-            cursor: unsafe { Address::zero() },
-            limit: unsafe { Address::zero() },
+            bump_pointer: unsafe { BumpPointer::new(Address::zero(), Address::zero()) },
             space,
             plan,
         }