e8374479f4
This is the set of changes required for snmalloc2 to be usable by the process sandboxing code and incorporates some API changes that reduce the amount of code required to embed snmalloc. Highlights: - Merge the config and back-end classes. - Everything in config is now global (all methods are static) - The GlobalState class is gone (all global state is managed by global methods on the config class) - LocalState is now a member of the config class, all methods are instance methods. - Not every configuration needs to use the lazy initialisation hooks. They now need to be provided only if they are used. If the configuration does not provide an `ensure_init` method, it is not called. If it does not provide an `is_initialised` method then the global initialisation state is not checked. - There is now an `snmalloc::Options` class that default initialises itself to the default behaviour. Every configuration must provide a `constexpr` instance of this class. Each flag can be separately overridden and new flags can be added without breaking any existing API consumers. The config classes are moved into the backend directory.
snmalloc
snmalloc is a high-performance allocator.
snmalloc can be used directly in a project as a header-only C++ library,
it can be LD_PRELOADed on Elf platforms (e.g. Linux, BSD),
and there is a crate to use it from Rust.
Its key design features are:
- Memory that is freed by the same thread that allocated it does not require any synchronising operations.
- Freeing memory in a different thread to initially allocated it, does not take any locks and instead uses a novel message passing scheme to return the memory to the original allocator, where it is recycled. This enables 1000s of remote deallocations to be performed with only a single atomic operation enabling great scaling with core count.
- The allocator uses large ranges of pages to reduce the amount of meta-data required.
- The fast paths are highly optimised with just two branches on the fast path for malloc (On Linux compiled with Clang).
- The platform dependencies are abstracted away to enable porting to other platforms.
snmalloc's design is particular well suited to the following two difficult scenarios that can be problematic for other allocators:
- Allocations on one thread are freed by a different thread
- Deallocations occur in large batches
Both of these can cause massive reductions in performance of other allocators, but do not for snmalloc.
Comprehensive details about snmalloc's design can be found in the accompanying paper, and differences between the paper and the current implementation are described here. Since writing the paper, the performance of snmalloc has improved considerably.
Further documentation
Contributing
This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.
When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.
This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.