RFR: 8328944: NMT reports "unknown" memory

[Thomas Stuefe]

On Fri, 1 Nov 2024 20:44:50 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

> We use mtNone value in several functions default parameters, which may show up in NMT reports.
> 
> We address this, by removing the default value and forcing, where possible, for the callers to declare NMT tag that reflects the usage.
> 
> Eventually the goal would be not to use mtNone anywhere, but we are not there quite yet.
> 
> TODO: update copyrights.
> 
> Testing: undergoing MARCH5 tier1-5 ...

In case this does not come across: I really welcome fixing unnecessary "mtNone" uses. I would like to see a nuanced approach though. The rule should be to try to use the correct tag at reservation. But exceptions should be allowed:
- if the tag is not clear at reservation, any other tag than mtNone (or the proposed mtAny) would be wrong
- if it makes the code a lot more brittle because reservation is "smeared" across many different mmap calls in many conditional branches. In that case, it is easier to tag the whole range after all that reservation business is done, outside the conditional branches.

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PR Comment: https://git.openjdk.org/jdk/pull/21843#issuecomment-2456635960