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perf(alloc): skip `*_aligned calls when alignment fits default - #170

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perf(alloc): skip `*_aligned calls when alignment fits default#170
chirizxc wants to merge 1 commit into
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chirizxc:fast-path

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@chirizxc chirizxc commented Aug 7, 2026 •
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For my library, this provides a small speedup (about ~3.2%):

❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0514s        1.00x      15.39 MB     0.384s
mimalloc              0.0438s        1.17x      15.68 MB     0.331s
fp-mimalloc           0.0408s        1.26x      15.76 MB     0.306s
❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0493s        1.00x      15.25 MB     0.360s
mimalloc              0.0437s        1.13x      15.75 MB     0.321s
fp-mimalloc           0.0415s        1.19x      15.58 MB     0.316s
❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0530s        1.00x      15.20 MB     0.371s
mimalloc              0.0436s        1.22x      15.50 MB     0.322s
fp-mimalloc           0.0440s        1.21x      15.69 MB     0.321s
❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0541s        1.00x      15.33 MB     0.376s
mimalloc              0.0415s        1.30x      15.62 MB     0.306s
fp-mimalloc           0.0409s        1.32x      15.52 MB     0.317s
❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0494s        1.00x      15.17 MB     0.356s
mimalloc              0.0425s        1.16x      15.70 MB     0.323s
fp-mimalloc           0.0412s        1.20x      15.83 MB     0.322s
❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0540s        1.00x      15.18 MB     0.386s
mimalloc              0.0430s        1.26x      15.52 MB     0.321s
fp-mimalloc           0.0414s        1.30x      15.81 MB     0.313s
❯ py benchmark/b.py
file: example.toml
size: 3.93 KiB
runs: 1,000 x 5

allocator                 time    vs default        memory        wall
--------------------------------------------------------------------------
default               0.0512s        1.00x      15.14 MB     0.364s
mimalloc              0.0464s        1.10x      15.59 MB     0.335s
fp-mimalloc           0.0446s        1.15x      15.55 MB     0.321s

chirizxc
chirizxc commented Aug 7, 2026
View reviewed changes
Comment thread src/lib.rs
Comment on lines +86 to +96
unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
mi_free(ptr as *mut c_void);
}

#[inline]
unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
mi_free(ptr as *mut c_void);
unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
if layout.align() <= MIN_MIMALLOC_ALIGNMENT {
mi_zalloc(layout.size()) as *mut u8
} else {
mi_zalloc_aligned(layout.size(), layout.align()) as *mut u8
}

@chirizxc chirizxc Aug 7, 2026

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chirizxc
chirizxc commented Aug 7, 2026
View reviewed changes
Comment thread src/lib.rs
Comment on lines 113 to 168
#[test]
fn it_frees_allocated_memory() {
unsafe {
let layout = Layout::from_size_align(8, 8).unwrap();
let alloc = MiMalloc;
let layout = Layout::from_size_align(8, 8).unwrap();
let alloc = MiMalloc;

let ptr = alloc.alloc(layout);
alloc.dealloc(ptr, layout);
}
let ptr = unsafe { alloc.alloc(layout) };
unsafe { alloc.dealloc(ptr, layout) };
}

#[test]
fn it_frees_allocated_big_memory() {
unsafe {
let layout = Layout::from_size_align(1 << 20, 32).unwrap();
let alloc = MiMalloc;
let layout = Layout::from_size_align(1 << 20, 32).unwrap();
let alloc = MiMalloc;

let ptr = alloc.alloc(layout);
alloc.dealloc(ptr, layout);
}
let ptr = unsafe { alloc.alloc(layout) };
unsafe { alloc.dealloc(ptr, layout) };
}

#[test]
fn it_frees_zero_allocated_memory() {
unsafe {
let layout = Layout::from_size_align(8, 8).unwrap();
let alloc = MiMalloc;
let layout = Layout::from_size_align(8, 8).unwrap();
let alloc = MiMalloc;

let ptr = alloc.alloc_zeroed(layout);
alloc.dealloc(ptr, layout);
}
let ptr = unsafe { alloc.alloc_zeroed(layout) };
unsafe { alloc.dealloc(ptr, layout) };
}

#[test]
fn it_frees_zero_allocated_big_memory() {
unsafe {
let layout = Layout::from_size_align(1 << 20, 32).unwrap();
let alloc = MiMalloc;
let layout = Layout::from_size_align(1 << 20, 32).unwrap();
let alloc = MiMalloc;

let ptr = alloc.alloc_zeroed(layout);
alloc.dealloc(ptr, layout);
}
let ptr = unsafe { alloc.alloc_zeroed(layout) };
unsafe { alloc.dealloc(ptr, layout) };
}

#[test]
fn it_frees_reallocated_memory() {
unsafe {
let layout = Layout::from_size_align(8, 8).unwrap();
let alloc = MiMalloc;
let layout = Layout::from_size_align(8, 8).unwrap();
let alloc = MiMalloc;

let ptr = alloc.alloc(layout);
let ptr = alloc.realloc(ptr, layout, 16);
alloc.dealloc(ptr, layout);
}
let ptr = unsafe { alloc.alloc(layout) };
let ptr = unsafe { alloc.realloc(ptr, layout, 16) };
unsafe { alloc.dealloc(ptr, layout) };
}

#[test]
fn it_frees_reallocated_big_memory() {
unsafe {
let layout = Layout::from_size_align(1 << 20, 32).unwrap();
let alloc = MiMalloc;
let layout = Layout::from_size_align(1 << 20, 32).unwrap();
let alloc = MiMalloc;

let ptr = alloc.alloc(layout);
let ptr = alloc.realloc(ptr, layout, 2 << 20);
alloc.dealloc(ptr, layout);
}
let ptr = unsafe { alloc.alloc(layout) };
let ptr = unsafe { alloc.realloc(ptr, layout, 2 << 20) };
unsafe { alloc.dealloc(ptr, layout) };
}
}

@chirizxc chirizxc Aug 7, 2026

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Not everything inside those blocks was unsafe

@chirizxc chirizxc mentioned this pull request Aug 9, 2026
Merged
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