rustwasm/wee_alloc

Investigate making the free list doubly linked

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#27 opened on Feb 23, 2018

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Description

Summary

Investigate rounding up allocations to at least two words, and making the free list doubly linked.

Motivation

This could simplify code, maybe shrink code size, and lessen fragmentation.

Details

  • We could remove deferred consolidation of cells. Simplifying code and hopefully also shrinking code size.

  • We could always consolidate a free cell with both of its neighbors, if they are also free. Right now we can only do one or the other because the free list is singly linked, and doesn't afford these kinds of manipulations in O(1) time.

  • Downside is that heap allocations of size < 2 words get rounded up. I think this is probably an OK choice.

  • We would make FreeCell have another link prev_free_raw that is the previous free list pointer.

  • Anywhere we insert into or remove from the free list, we would need to make sure that the new link is kept valid.

Happy to mentor anyone who wants to try their hand at this!

Contributor guide

Research direction
Study the current singly linked free list implementation in wee alloc, then design a doubly linked version. Focus on understanding how cells are consolidated and how to update the prev pointer during insert/remove operations.
Tech stack
rust
Domain
backend
Issue type
Research
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Rustdata structures
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65