RFR: JDK-8296360: Track native memory used by zlib via NMT

[Alan Bateman]

On Fri, 4 Nov 2022 14:35:00 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> This patch adds NMT tracking to the zlib.
> 
> *Please note: we currently discuss whether NMT can be expanded across the JDK in this ML discussion [1]. This PR depends on the outcome of that discussion and won't proceed unless greenlighted. But since [1] is stalled, I post the PR for RFR to get some feedback on the code itself and for people to try it out.*
> 
> NMT tracks hotspot native allocations but does not cover the JDK (apart from small exceptions). But the native memory
> footprint of JDK libraries can be very significant. Recently we had a customer whose zlib footprint went into the ~40GB range. We analyzed the problem with an in-house memory tracker, but things would have been a lot simpler using NMT.
> 
> This patch instruments the zlib via zalloc hooks, which is minimally invasive. It does not touch zlib sources, so it works with both the bundled zlib and system zlib. All the instrumentation happens in the JVM zlib wrapper.
> 
> 
> -         j.u.zip (deflate) (reserved=624, committed=624)
>                             (malloc=624 #3) 
>  
> -         j.u.zip (inflate) (reserved=221377904, committed=221377904)
>                             (malloc=221377904 #60877) 
>  
> -               Zip (other) (reserved=8163446896, committed=8163446896)
>                             (malloc=8163446896 #182622) 
> 
> 
> [1] https://mail.openjdk.org/pipermail/core-libs-dev/2022-November/096197.html

I think it's a bit premature to mark this review. The discussion thread "Extend Native Memory Tracking over the JDK ?" needs more discussion and input from others. We need to be forward looking in those discussions as it is very likely that the JNI functions and memory allocation will move to Panama in the future. Also we need to think about the maintainable and be able to manage catagories in the libs code without needing to add to allocation.hpp - I suspect this is probably something you've thought about already.

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PR: https://git.openjdk.org/jdk/pull/10988