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Fallback when allocating a new chunk fails #111

Merged
merged 7 commits into from
May 26, 2021
Merged

Fallback when allocating a new chunk fails #111

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b9f5968
Change the alloc policy to allocate the current footer size
Kerollmops May 12, 2021
77e8a12
Try to allocate half the current footer if same size is rejected
Kerollmops May 12, 2021
d05ae1a
Try allocating a chunk always half the size of the previous size tried
Kerollmops May 12, 2021
5999c72
Check that the new chunk can hold the requested size
Kerollmops May 25, 2021
b3974de
A little big of wording
Kerollmops May 25, 2021
41c38db
Make sure that the requested chunk size is at least the default size
Kerollmops May 25, 2021
fd0738d
Make sure that the first chunk is at least the minimum chunk size
Kerollmops May 26, 2021
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39 changes: 24 additions & 15 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -632,20 +632,13 @@ impl Bump {
/// layout of the allocation request that triggered us to fall back to
/// allocating a new chunk of memory.
fn new_chunk(
old_size_with_footer: Option<usize>,
new_size_without_footer: Option<usize>,
requested_layout: Option<Layout>,
prev: Option<NonNull<ChunkFooter>>,
) -> Option<NonNull<ChunkFooter>> {
unsafe {
// As a sane default, we want our new allocation to be about twice as
// big as the previous allocation
let mut new_size_without_footer =
if let Some(old_size_with_footer) = old_size_with_footer {
let old_size_without_footer = old_size_with_footer - FOOTER_SIZE;
old_size_without_footer.checked_mul(2)?
} else {
DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER
};
new_size_without_footer.unwrap_or(DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER);

// We want to have CHUNK_ALIGN or better alignment
let mut align = CHUNK_ALIGN;
Expand Down Expand Up @@ -681,7 +674,7 @@ impl Bump {
.unwrap_or_else(allocation_size_overflow);
let layout = layout_from_size_align(size, align);

debug_assert!(size >= old_size_with_footer.unwrap_or(0) * 2);
debug_assert!(requested_layout.map_or(true, |layout| size >= layout.size()));

let data = alloc(layout);
let data = NonNull::new(data)?;
Expand Down Expand Up @@ -1450,11 +1443,27 @@ impl Bump {
// Get a new chunk from the global allocator.
let current_footer = self.current_chunk_footer.get();
let current_layout = current_footer.as_ref().layout;
let new_footer = Bump::new_chunk(
Some(current_layout.size()),
Some(layout),
Some(current_footer),
)?;

// By default, we want our new chunk to be about twice as big
// as the previous chunk. If the global allocator refuses it,
// we try to divide it by half until it works or the requested
// size is smaller than the default footer size.
let mut base_size = (current_layout.size() - FOOTER_SIZE).checked_mul(2)?;
let min_new_chunk_size = layout.size().max(DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER);
let sizes = iter::from_fn(|| {
if base_size >= min_new_chunk_size {
let size = base_size;
base_size = base_size / 2;
Some(size)
} else {
None
}
});

let new_footer = sizes
.filter_map(|size| Bump::new_chunk(Some(size), Some(layout), Some(current_footer)))
.next()?;

debug_assert_eq!(
new_footer.as_ref().data.as_ptr() as usize % layout.align(),
0
Expand Down