RFR: 8267155: runtime/os/TestTracePageSizes times out [v4]

[Stefan Johansson]

On Tue, 18 May 2021 06:53:19 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> This Linux-specific test parses `/proc/self/smaps` using a dotall regular expression. If part of the expression don't match it explodes in complexity, leading to timeouts.
>> 
>> In our case, `VmFlags` tag was missing from smaps, which was introduced with kernel 3.8. I am actually not able to determine how slow they were; on one machine they ran for two hours before getting killed.
>> 
>> I tried to fiddle with the regular expression and gave up, instead opting to rewrite the parser to get a simple one-pass scan. This is way faster than before - on our old-kernel machines the tests complete in 2 minutes. On new kernels the test is a bit faster too.
>> 
>> In addition to rewriting the parser, I added code which copies the smaps file into the test directory before parsing it. I do this to minimize problems should the underlying proc fs content change while parsing, and to have a way to retain the parsed smaps files.
>> 
>> I also added a way to feed an external smaps file into the test. Of course the test would fail, but it was a way to test the parser.
>> 
>> Unfortunately, this does not make the test succeed. The timeouts are gone, but we have still have no way to know if TPHs are enabled or not. That is a separate issue though.
>> 
>> Thanks, Thomas
>
> Thomas Stuefe has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Update test/hotspot/jtreg/runtime/os/TestTracePageSizes.java
>    
>    Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
>  - Update test/hotspot/jtreg/runtime/os/TestTracePageSizes.java
>    
>    oops
>    
>    Co-authored-by: Aleksey Shipilëv <shade at redhat.com>

Did a quick test now with THP configured to `always` but running with `-XX:-UseLargePages -XX:-UseTransparentHugePages`. It gives me:

80000000-ffe00000 rw-p 00000000 00:00 0 
Size:            2095104 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
...
AnonHugePages:   2095104 kB
THPeligible:            1
VmFlags: rd wr mr mw me ac sd 

So no `hg` flag as expected.

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PR: https://git.openjdk.java.net/jdk/pull/4064