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A memory allocator that automatically reduces the memory footprint of C/C++ applications.
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README.md

Mesh: Compacting Memory Management for C/C++

Mesh is a drop in replacement for malloc(3) that compacts the heap without rewriting application pointers.

Mesh is described in an academic paper (PDF) that appeared at PLDI 2019.

Or watch this talk by Bobby Powers at Strange Loop:

Compacting the Uncompactable

Mesh runs on Linux; macOS support should be considered alpha-quality, and Windows is a work in progress.

Mesh has a standard C++ build process, and has no runtime dependencies other than libc-related libs:

$ git clone --recurse-submodules https://github.com/plasma-umass/mesh
$ cd mesh
$ ./configure; make; sudo make install
# example: run git with mesh as its allocator:
$ LD_PRELOAD=libmesh.so git status

Please open an issue if you have questions (or issues)!

Implementation Overview

Mesh is built on Heap Layers, an infrastructure for building high performance memory allocators in C++ (see paper for details.)

The entry point of the library is libmesh.cc. This file is where malloc, free and the instantiations of the Heap used for allocating program memory lives.

DEFINITIONS

  • Page: The smallest block of memory managed by the operating system, 4Kb on most architectures. Memory given to the allocator by the operating system is always in multiples of the page size, and aligned to the page size.
  • Span: A contiguous run of 1 or more pages. It is often larger than the page size to account for large allocations and amortize the cost of heap metadata.
  • Arena: A contiguous range of virtual address space we allocate out of. All allocations returned by malloc(3) reside within the arena.
  • GlobalHeap: The global heap carves out the Arena into Spans and performs meshing.
  • MiniHeap: Metadata for a Span -- at any time a live Span has a single MiniHeap owner. For small objects, MiniHeaps have a bitmap to track whether an allocation is live or freed.
  • ThreadLocalHeap: A collections of MiniHeaps and a ShuffleVector so that most allocations and free(3)s can be fast and lock-free.
  • ShuffleVector: A novel data structure that enables randomized allocation with bump-pointer-like speed.
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