RFR: 8263236: runtime/os/TestTracePageSizes.java fails on old kernels [v5]

[Aleksey Shipilev]

On Thu, 6 May 2021 14:05:18 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See the bug report for details. On some kernels, the madvise hint is not reflected in `/proc/smaps`.
>> Rough kernel bisection shows that the hints are reliable since kernel 4.15.
>> There are plenty of changes between 4.14.17 and 4.15, none seem obvious as the culprits.
>> 
>> Additional testing:
>>  - [x] Test with kernel 5.4.0 (still passes)
>>  - [x] Test with kernel 4.9.0 (used to fail, now passes)
>>  - [x] Test with kernel 4.15 (still passes)
>>  - [x] Test with kernel 4.14.17 (used to fail, now passes)
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   More precise version, after rough kernel bisection

Okay, I did a rough bisect over pre-built Debian kernels, and that points to `4.15` as the first kernel that works. I updated the PR changeset and PR description accordingly. I am still struggling to find a particular commit that solved it, so I can explain to myself why this works... Anyhow, the version check would not get more precise that this, since we only have major and minor OS versions.

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PR: https://git.openjdk.java.net/jdk/pull/3415