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Improve the documentation of the memory block size growth feature
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nical committed Jan 31, 2025
1 parent 5d4b861 commit 86a9379
Showing 1 changed file with 26 additions and 13 deletions.
39 changes: 26 additions & 13 deletions src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -282,20 +282,22 @@ impl Default for AllocatorDebugSettings {

/// The sizes of the memory blocks that the allocator will create.
///
/// Useful for tuning the allocator to your application's needs. For example most games will be fine with the defaultsize
/// Useful for tuning the allocator to your application's needs. For example most games will be fine with the default
/// values, but eg. an app might want to use smaller block sizes to reduce the amount of memory used.
///
/// Clamped between 4MB and 256MB, and rounds up to the nearest multiple of 4MB for alignment reasons.
///
/// # Fixed or growable block size
///
/// This structure represents ranges of allowed sizes for shared memory blocks.
/// By default, If the bounds of a given range are equal, the allocator will
/// be configured to used a fixed memory block size for shared allocations.
/// By default, if the upper/max bounds are not extended using `with_max_*_memblock_size`,
/// the allocator will be configured to use a fixed memory block size for shared
/// allocations.
///
/// Otherwise, the allocator will pick a memory block size within the specifed
/// range, dependending on the number of existing allocations for the memory
/// range, depending on the number of existing allocations for the memory
/// type.
///
/// As a rule of thumb, the allocator will start with the minimum block size
/// and double the size with each new allocation, up to the specified maximum
/// block size. This growth is tracked independently for each memory type.
Expand All @@ -321,26 +323,34 @@ impl Default for AllocatorDebugSettings {
pub struct AllocationSizes {
/// The initial size of the memory blocks that will be created for the GPU only memory type.
///
/// The size of new device memory blocks doubles each time a new block is needed, up to
/// [`AllocationSizes::max_device_memblock_size`].
///
/// Defaults to 256MB.
min_device_memblock_size: u64,
/// The size of device memory blocks doubles each time a new allocation is needed, up to
/// `device_maximum_memblock_size`.
/// The maximum size for shared device memory blocks.
///
/// Defaults to the value of [`AllocationSizes::min_device_memblock_size`].
max_device_memblock_size: u64,
/// The size of the memory blocks that will be created for the CPU visible memory types.
/// The initial size of the memory blocks that will be created for the CPU visible memory types.
///
/// The size new of host memory blocks doubles each time a new block is needed, up to
/// [`AllocationSizes::max_host_memblock_size`].
///
/// Defaults to 64MB.
min_host_memblock_size: u64,
/// The size of host memory blocks doubles each time a new allocation is needed, up to
/// `host_maximum_memblock_size`.
/// The maximum size for shared host memory blocks.
///
/// Defaults to the value of [`AllocationSizes::min_host_memblock_size`].
max_host_memblock_size: u64,
}

impl AllocationSizes {
/// Sets the minimum device and host memory block sizes.
///
/// The maximum block sizes are initialized to the minimum sizes and
/// can be changed using `with_max_device_memblock_size` and
/// `with_max_host_memblock_size`.
/// can be increased using [`AllocationSizes::with_max_device_memblock_size`] and
/// [`AllocationSizes::with_max_host_memblock_size`].
pub fn new(device_memblock_size: u64, host_memblock_size: u64) -> Self {
let device_memblock_size = Self::adjust_memblock_size(device_memblock_size, "Device");
let host_memblock_size = Self::adjust_memblock_size(host_memblock_size, "Host");
Expand Down Expand Up @@ -389,8 +399,11 @@ impl AllocationSizes {
}

/// Used internally to decide the size of a shared memory block
/// based withing the allowed range, based on the number of
/// existing allocations
/// based within the allowed range, based on the number of
/// existing allocations. The more blocks there already are
/// (where the requested allocation didn't fit), the larger
/// the returned memory block size is going to be (up to
/// `max_*_memblock_size`).
pub(crate) fn get_memblock_size(&self, is_host: bool, count: usize) -> u64 {
let (min_size, max_size) = if is_host {
(self.min_host_memblock_size, self.max_host_memblock_size)
Expand Down

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