RFR: JDK-8296931: NMT tests slowed down considerably by JDK-8242181

[David Holmes]

On Mon, 14 Nov 2022 12:43:41 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> We noticed that NMT tests on our slower PPC machines started failing.
> 
> The reason is that NMT detail reports have become 2-5x slower. This is caused by us now parsing the dwarf debug information to extract source information for each PC in each call stack. That is nice but costly.
> 
> The slowdown is not limited to PPC, it affects all Elf platforms. On my Linux x64 box, runtime/NMT/VirtualAllocCommitMerge.java increased from 20 to 90 seconds.
> 
> ---
> 
> This patch simply removes source info from NMT call stacks. They are not that important for pinpointing leaks and such. I considered more involved solutions, like making them optional via an argument to the NMT report command, but decided against it. The added benefit would be small, not worth much complexity.
> 
> With this patch, on my box with -conc 4 all NMT together are about 2.5 x faster (2m56 -> 1m09).

Sorry have been swamped past couple of days.

>From the style guide:

> As a general rule don't add bug numbers to comments (they would soon overwhelm the code). But if the bug report contains significant information that can't reasonably be added as a comment, then refer to the bug report.

I would probably not have added it in this case but its a judgment call.

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PR: https://git.openjdk.org/jdk/pull/11135