NUMA Memory Planner
Plan memory allocation across NUMA nodes to minimize remote memory access latency.
About NUMA Memory Planner
On multi-socket (NUMA — Non-Uniform Memory Access) systems, each CPU socket has its own locally-attached memory; accessing memory attached to a different socket ('remote' access) crosses an inter-socket interconnect and costs additional latency, typically 50-100ns on top of local access latency. The local access ratio — measurable via `numastat` or perf's NUMA events — directly determines average effective memory latency; tools like numactl let you bind a process's memory allocations and CPU execution to the same node to maximize this ratio.
Formula
Average memory latency
avg_latency = local_ratio × local_latency + remote_ratio × (local_latency + remote_penalty)
- r_l
- local access ratio
- L_local
- local access latency
- P_remote
- remote access penalty
Worked example
With the default values below, NUMA Memory Planner returns Local Access Ratio of 75.00%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Total Memory Accesses (sampled)minimum 1
- 1,000,000
- Local Node Accessesminimum 0
- 750,000
- Local Access Latency (ns)minimum 1
- 80
- Remote Access Penalty (ns, additional)minimum 0
- 75
Results
- Local Access Ratio
- 75.00%
- Average Memory Access Latency (ns)
- 98.75
- Latency Overhead vs. All-Local
- 23.44%
- Remote Accesses
- 250,000
- Recommendation
- Reasonable locality — consider numactl --membind or --cpunodebind for latency-sensitive workloads to push this higher.
Step by step
- 1Values used
- 2Average memory latency
- 3Local Access Ratio= 75.00
- 4Average Memory Access Latency (ns)= 98.75
- 5Latency Overhead vs. All-Local= 23.44
- 6Remote Accesses= 250,000
- 7Recommendation= Reasonable locality — consider numactl --membind or --cpunodebind for latency-sensitive workloads to push this higher.
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How do I check NUMA locality on a running system?
`numastat -p <pid>` shows a process's memory allocation split across NUMA nodes, and `numastat` alone shows system-wide hit/miss statistics (numa_hit vs numa_miss/numa_foreign) that indicate how often memory ended up on a different node than where it was allocated from.
How do I force a process to use local memory?
`numactl --cpunodebind=0 --membind=0 <command>` pins both CPU execution and memory allocation to NUMA node 0, ensuring the process's memory accesses stay local. For already-running processes, `numactl` alone can't rebind, but taskset combined with careful memory migration tools can help.
Does NUMA matter on single-socket systems?
Largely no for cross-socket effects, but some modern single-socket CPUs still expose multiple NUMA nodes internally (e.g. AMD's chiplet designs can present each CCX or CCD as a separate NUMA node), so it's worth checking `numactl --hardware` even on nominally single-socket servers.