Crate win_numa_sys 

Memory-safe Rust over the Windows NUMA APIs.

Windows provides some NUMA concepts; this crate builds library notions on top of them. Whether a client uses them is up to the client.

What is here

• NumaNode – a node number, as Windows numbers them.
• NumaBuffer – an owned allocation made with VirtualAllocExNuma and released with VirtualFree, so a buffer can be placed on a chosen node rather than wherever the default allocator lands it.
• highest_numa_node and volume_numa_node – the two questions Windows will answer about nodes, wrapped so a caller can find a node to pass without writing the FFI themselves.

NumaBuffer implements io-buffers’ IoBuf and IoBufMut, so it can be handed to a ring as it is. This crate defines no buffer trait of its own.

What is not here, and will not be

Any opinion about which node anything should use. This crate reports what Windows says and allocates where it is told. It does not map a file to a node, does not shard anything, and does not choose a node on a caller’s behalf. Those are workload decisions, and a consumer on hardware this workspace has never seen is better placed to take them.

The -sys suffix is that promise, and it is the repository’s meaning of the suffix rather than a convention borrowed from elsewhere: thin over Win32, memory-safe, adding no policy.

A node argument is a preference, not an instruction

The underlying parameter says so in its own name – nndPreferred. A successful allocation is therefore not evidence that the pages landed on the node that was asked for, and code that needs to know must observe rather than assume. Two measured facts about that, both from this workspace:

• Committed pages are demand-zero, so until something writes to them no physical page has been drawn from the preferred node at all. A caller measuring placement must fault the pages in first.
• An invalid node is refused, and u32::MAX is not a test of that: it is the API’s own no-preference sentinel, accepted by design. A measurement that asks for u32::MAX and sees it succeed has measured the sentinel, not a range check. NumaBuffer’s tests use u32::MAX - 1.

Observing where pages actually landed needs QueryWorkingSetEx, which lives in windows-placement-probe today and is a candidate to move here; see that crate’s peer_index_cache.

Structs

NumaBuffer

An owned buffer allocated with VirtualAllocExNuma, freed with VirtualFree on drop.

NumaNode

A NUMA node number, as Windows numbers them.

Functions

highest_numa_node

The highest node number this machine reports, if it answers.

volume_numa_node

The NUMA node handle’s volume reports, if it reports one.