JAX London, 4–7 October 2021
The Online Conference for Java & Software Innovation

No Free Lunch? Memory Allocation in the JVM

Session
Where the Java community meets online! Thank you for joining! See you in 2021 Register now
Infos
Tuesday, October 6 2020
15:00 - 15:45

Ever wondered how memory allocation on the JVM works?The Java Virtual Machine features many generational garbage collectors that also use pointer bumping for allocation. The combination of these two techniques gives a fast allocation and collection path which has led to a commonly held belief in the Java community that allocation in general is cheap. This talk will challenge that belief by looking at what happens outside of the fast path and considering the impact of even fast path allocation on other parts of the system, such as caches and memory bandwidth.

You will see how optimisations from the JIT can reduce or eliminate many allocations but how reasoning about when these happen can be almost impossible from glancing at code. Examples will introduce you to common problems and tooling you can use to understand the allocation behaviour of your code.

From attending this talk you will understand:

– How allocation works in modern JVM Garbage Collectors

– Why allocation isn’t necessarily as cheap as it seems

– Why the JVM makes it difficult to reason about allocation behaviour by code examination

– What kind of tooling you can use to understand the real allocation behaviour of your code

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