39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
# Difference from published paper
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This document outlines the changes that have diverged from
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[the published paper](snmalloc.pdf) on `snmalloc`.
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1. Link no longer terminates the bump-free list. The paper describes a
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complex invariant for how the final element of the bump-free list can
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also be the link node.
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We now have a much simpler invariant. The link is either 1, signifying
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the block is completely full. Or not 1, signifying it has at least one
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free element at the offset contained in link, and that contains the DLL
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node for this sizeclass.
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The bump-free list contains additional free elements, and the remaining
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bump allocated space.
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The value 1, is never a valid bump allocation value, as we initially
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allocate the first entry as the link, so we can use 1 as the no more bump
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space value.
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2. Separate Bump/Free list. We have separate bump ptr and free list. This
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is required to have a "fast free list" in each allocator for each
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sizeclass. We bump allocate a whole os page (4KiB) worth of allocations
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in one go, so that the CPU predicts the free list path for the fast
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path.
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3. Per allocator per sizeclass fast free list. Each allocator has an array
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for each small size class that contains a free list of some elements for
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that sizeclass. This enables a very compressed path for the common
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allocation case.
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4. We now store a direct pointer to the next element in each slabs free list
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rather than a relative offset into the slab. This enables list
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calculation on the fast path.
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[2-4] Are changes that are directly inspired by
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(mimalloc)[http://github.com/microsoft/mimalloc]. |