RFR: 8317453: NMT: Performance benchmarks are needed to measure speed and memory

[Afshin Zafari]

On Tue, 25 Feb 2025 21:52:48 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

> Please review this addition of an internal benchmark, mostly of interest to those working with NMT.
> 
> This benchmark allows us to record a pattern of memory allocation operations (i.e. `malloc`, `realloc` and `free`) as well as the virtual memory allocations (i.e. `VirtualMemoryTracker::add_reserved_region`, etc.) and record those into files.
> 
> Later we can use that recording to _play back_ the pattern with different code or settings to compare the performance.
> 
> The goal of this benchmark is for anyone working on NMT to be able to measure and prove whether their improvement helps or regresses the performance.
> 
> ### To use it:
> 
> To record pattern of allocations of memory calls:
> 
> `NMTRecordMemoryAllocations=0x7FFFFFFF ./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NativeMemoryTracking=summary -jar build/macosx-aarch64-server-release/images/jdk/demo/jfc/J2Ddemo/J2Ddemo.jar`
> 
> OR to record pattern of allocations of virtual memory calls:
> 
> `NMTRecordVirtualMemoryAllocations=0x7FFFFFFF ./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NativeMemoryTracking=summary -jar build/macosx-aarch64-server-release/images/jdk/demo/jfc/J2Ddemo/J2Ddemo.jar`
> 
> This will result in the file:
> -  hs_nmt_pid22770_allocs_record.log (is the chronological record of the the desired operations)
> OR
> - hs_nmt_pid22770_virtual_allocs_record.log (is the chronological record of the desired operations)
> 
> And 2 additional files:
> - hs_nmt_pid22770_info_record.log (is the record of default NMT memory overhead and the NMT state)
> - hs_nmt_pid22770_threads_record.log (is the record of thread names that can be retrieved later when processing)
> 
> 
> then to actually run the benchmark:
> 
> NMTBenchmarkRecordedPID=22770 ./build/macosx-aarch64-server-release/xcode/build/jdk/bin/java -XX:+UnlockDiagnosticVMOptions -XX:NativeMemoryTracking=summary
> 
> ### Usage:
> 
> See the issue for more details and the design document.

Thanks for the nice idea and efforts to implement it.
I have some questions that are written in comments.

src/hotspot/share/nmt/memTracker.cpp line 57:

> 55: 
> 56: void MemTracker::initialize() {
> 57:   NMT_LogRecorder::initialize();

Why we initialize the log-recorder even if NMT is not enabled?

src/hotspot/share/nmt/memTracker.cpp line 100:

> 98:   }
> 99: 
> 100:   NMT_LogRecorder::replay();

If the pid is saved in the corresponding env-var and there is a recording file, `replay()` will run and play at every time JVM starts (all the JTREG tests for example). Perhaps we don't want this.

src/hotspot/share/nmt/memTracker.hpp line 1:

> 1: /*

In memTracker, there are also functions for `Arena` allocations. Why they are not include in the LogRecording?

src/hotspot/share/nmt/memTracker.hpp line 91:

> 89:       ptr = MallocTracker::record_malloc(mem_base, size, mem_tag, stack, old_base);
> 90:     }
> 91:     NMT_MemoryLogRecorder::record_malloc(mem_tag, size, mem_base, &stack, old_base);

Can we move the `NMT_MemoryLogRecorder::record_malloc` inside the `MallocTracker::record_malloc`?
Then we are also sure that thee recording only happens when NMT is enabled.
The same applies to other malloc methods and `VMT::record_xxxxx` methods.

-------------

PR Review: https://git.openjdk.org/jdk/pull/23786#pullrequestreview-2732052712
PR Review Comment: https://git.openjdk.org/jdk/pull/23786#discussion_r2022462035
PR Review Comment: https://git.openjdk.org/jdk/pull/23786#discussion_r2022468313
PR Review Comment: https://git.openjdk.org/jdk/pull/23786#discussion_r2022478241
PR Review Comment: https://git.openjdk.org/jdk/pull/23786#discussion_r2022472641