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[EXPERIMENT] Pass buffer capacity and alignment to the allocator #9812

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[EXPERIMENT] Pass buffer capacity and alignment to the allocator #9812

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180 changes: 7 additions & 173 deletions vortex-buffer/src/allocation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,9 @@
// SPDX-FileCopyrightText: Copyright the Vortex contributors

//! Allocator-backed storage for Vortex buffers.
//!
//! Each allocation retains its base pointer and original layout through slicing and ownership
//! transfers. Buffer data pointers and logical alignments do not change the layout used to free it.

use std::alloc::Layout;
use std::any::Any;
Expand All @@ -22,7 +25,7 @@ use crate::BufferMut;

/// An allocator that can back a Vortex buffer.
///
/// Vortex over-allocates raw storage and aligns the buffer within it.
/// Buffer allocations pass their byte capacity and effective alignment through [`Layout`].
pub trait BufferAllocator: Allocator + Debug + Send + Sync + 'static {}

impl<A> BufferAllocator for A where A: Allocator + Debug + Send + Sync + 'static {}
Expand Down Expand Up @@ -235,7 +238,9 @@ unsafe impl Allocator for StaticBufferAllocator {
static STATIC_ALLOCATOR: BufferAllocatorRef = BufferAllocatorRef(None);

pub(crate) struct Allocation {
/// Allocation base, or an aligned dangling pointer when the layout has zero size.
ptr: NonNull<u8>,
/// Layout used to allocate this block. Allocator excess is not exposed as buffer capacity.
layout: Layout,
allocator: BufferAllocatorRef,
}
Expand Down Expand Up @@ -318,6 +323,7 @@ impl Allocation {
}

pub(crate) fn grow(&mut self, new_layout: Layout) {
debug_assert!(new_layout.size() >= self.layout.size());
let allocation = if self.layout.size() == 0 {
self.allocator.allocate(new_layout)
} else {
Expand Down Expand Up @@ -363,175 +369,3 @@ impl BufferBacking {
}
}
}

#[cfg(test)]
mod tests {
use std::alloc::Layout;
use std::ptr::NonNull;
use std::sync::Arc;
use std::sync::atomic::AtomicUsize;
use std::sync::atomic::Ordering;

use allocator_api2::alloc::AllocError;
use allocator_api2::alloc::Allocator;
use allocator_api2::alloc::Global;
use rstest::rstest;
use vortex_error::VortexResult;
use vortex_error::vortex_err;

use crate::Alignment;
use crate::BufferAllocatorRef;
use crate::BufferMut;

#[derive(Clone, Debug, Default)]
struct TrackingAllocator {
state: Arc<TrackingState>,
}

#[derive(Debug, Default)]
struct TrackingState {
allocations: AtomicUsize,
deallocations: AtomicUsize,
grows: AtomicUsize,
alignment: AtomicUsize,
}

// SAFETY: this forwards all memory operations to Global and only records call metadata.
unsafe impl Allocator for TrackingAllocator {
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
self.state.allocations.fetch_add(1, Ordering::Relaxed);
self.state
.alignment
.store(layout.align(), Ordering::Relaxed);
Global.allocate(layout)
}

unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
self.state.deallocations.fetch_add(1, Ordering::Relaxed);
// SAFETY: the caller passes the pointer and layout returned by Global.
unsafe { Global.deallocate(ptr, layout) }
}

unsafe fn grow(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
self.state.grows.fetch_add(1, Ordering::Relaxed);
// SAFETY: the caller upholds the Allocator contract.
unsafe { Global.grow(ptr, old_layout, new_layout) }
}
}

#[test]
fn allocator_identity() {
let static_allocator = BufferAllocatorRef::statically_allocated();
assert!(static_allocator.ptr_eq(&BufferAllocatorRef::statically_allocated()));

let custom_allocator = BufferAllocatorRef::new(TrackingAllocator::default());
assert!(custom_allocator.ptr_eq(&custom_allocator.clone()));
assert!(!custom_allocator.ptr_eq(&static_allocator));
assert!(!custom_allocator.ptr_eq(&BufferAllocatorRef::new(TrackingAllocator::default())));
}

#[test]
fn allocation_lives_until_last_view() {
let allocator = TrackingAllocator::default();
let state = Arc::clone(&allocator.state);
let buffer = BufferAllocatorRef::new(allocator)
.copy_from([1u32, 2, 3, 4])
.freeze();
let view = buffer.slice(0..2);

assert_eq!(state.allocations.load(Ordering::Relaxed), 1);
assert_eq!(
state.alignment.load(Ordering::Relaxed),
Alignment::of::<u8>().as_usize()
);
drop(buffer);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 0);
drop(view);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 1);
}

#[rstest]
fn buffer_growth_uses_allocator_grow(#[values(4, 64, 4096)] alignment: usize) {
let allocator = TrackingAllocator::default();
let state = Arc::clone(&allocator.state);
let alignment = Alignment::new(alignment);
let mut buffer =
BufferAllocatorRef::new(allocator).with_capacity_aligned::<u32>(1, alignment);
let initial_capacity = buffer.capacity();
buffer.extend(std::iter::repeat_n(7, initial_capacity));

buffer.push(u32::MAX);
assert!(alignment.is_ptr_aligned(buffer.as_ptr()));

assert_eq!(&buffer[..initial_capacity], vec![7; initial_capacity]);
assert_eq!(buffer[initial_capacity], u32::MAX);
assert_eq!(state.allocations.load(Ordering::Relaxed), 1);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 0);
assert_eq!(state.grows.load(Ordering::Relaxed), 1);

drop(buffer);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 1);
}

#[test]
fn zero_capacity_does_not_allocate() {
let allocator = TrackingAllocator::default();
let state = Arc::clone(&allocator.state);
let mut buffer = BufferAllocatorRef::new(allocator).with_capacity::<u32>(0);

assert_eq!(buffer.capacity(), 0);
assert!(Alignment::DEFAULT_ALIGNMENT.is_offset_aligned(buffer.as_ptr().addr()));
assert_eq!(state.allocations.load(Ordering::Relaxed), 0);

buffer.push(42);

assert_eq!(buffer.as_slice(), [42]);
assert_eq!(state.allocations.load(Ordering::Relaxed), 1);
assert_eq!(state.grows.load(Ordering::Relaxed), 0);
}

#[test]
fn empty_buffers_preserve_allocator_without_allocating() -> VortexResult<()> {
let allocator = TrackingAllocator::default();
let state = Arc::clone(&allocator.state);
let allocator = BufferAllocatorRef::new(allocator);
let buffer = BufferMut::<u32>::zeroed_in(0, allocator.clone());
let buffer = buffer.freeze();
let copy = buffer.clone().into_mut();
assert!(copy.allocator().ptr_eq(&allocator));
let mut buffer = buffer
.try_into_mut()
.map_err(|_| vortex_err!("unique buffer"))?;
buffer.reserve(0);
assert!(buffer.is_empty());
assert!(buffer.allocator().ptr_eq(&allocator));
drop((copy, buffer));
assert_eq!(state.allocations.load(Ordering::Relaxed), 0);
assert_eq!(state.grows.load(Ordering::Relaxed), 0);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 0);
Ok(())
}

#[test]
fn shared_into_mut_preserves_allocator() {
let allocator = TrackingAllocator::default();
let state = Arc::clone(&allocator.state);
let allocator = BufferAllocatorRef::new(allocator);
let original = allocator.copy_from([1u32, 2, 3]).freeze();
let mut copy = original.clone().into_mut();
assert!(copy.allocator().ptr_eq(&allocator));
copy[0] = 42;
assert_eq!(original.as_slice(), [1, 2, 3]);
assert_eq!(copy.as_slice(), [42, 2, 3]);
assert_eq!(state.allocations.load(Ordering::Relaxed), 2);
drop(copy);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 1);
drop(original);
assert_eq!(state.deallocations.load(Ordering::Relaxed), 2);
}
}
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