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snmalloc is a high-performance allocator.snmalloc can be used directly in a project as a header-only C++ library,it can beLD_PRELOADed on Elf platforms (e.g. Linux, BSD),and there is acrate to use it from Rust.

Its key design features are:

• Memory that is freed by the same thread that allocated it does not require anysynchronising operations.
• Freeing memory in a different thread to initially allocated it, does not takeany locks and instead uses a novel message passing scheme to return thememory to the original allocator, where it is recycled. This enables 1000s of remotedeallocations to be performed with only a single atomic operation enabling greatscaling with core count.
• The allocator uses large ranges of pages to reduce the amount of meta-datarequired.
• The fast paths are highly optimised with just two branches on the fast pathfor 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 difficultscenarios 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, butdo not for snmalloc.

The implementation of snmalloc has evolved significantly since theinitial paper.The mechanism for returning memory to remote threads has remained, but most of the meta-data layout has changed.We recommend you readdocs/security to find out about the current design, andif you want to dive into the codedocs/AddressSpace.md provides a good overview of the allocation and deallocation paths.

There is a hardened version of snmalloc, it contains

• Randomisation of the allocations' relative locations,
• Most meta-data is stored separately from allocations, and is protected with guard pages,
• All in-band meta-data is protected with a novel encoding that can detect corruption, and
• Provides amemcpy that automatically checks the bounds relative to the underlying malloc.

A more comprehensive write up is indocs/security.

• Instructions for building snmalloc
• Instructions for porting snmalloc

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