RFR: 8271195: Use largest available large page size smaller than LargePageSizeInBytes when available [v8]

[Stefan Johansson]

On Mon, 21 Feb 2022 13:11:39 GMT, Swati Sharma <duke at openjdk.java.net> wrote:

>> Hi Team,
>> 
>> In this patch I have fixed two issues related to large pages, following is the summary of changes :-
>> 
>> 1. Patch fixes existing large page allocation functionality where if a commit over 1GB pages fails allocation should happen over next small page size i.e. 2M where as currently its happening over 4kb pages resulting into significant TLB miss penalty.
>> Patch includes new JTREG Test case covering various scenarios for checking the correct explicit page allocation according ​to the 1G, 2M, 4K priority.
>> 2. While attempting commit over larger pages we first try to reserve requested bytes over the virtual address space, in case commit to large page fails we should be un reserving entire reservation to avoid leaving any leaks in virtual address space.
>> 
>> ​
>> Please find below the performance data with and without patch for the JMH benchmark included with the patch.
>> 
>> ![image](https://user-images.githubusercontent.com/96874289/152189587-4822a4ca-f5e2-4621-b405-0da941485143.png)
>> 
>> 
>> Please review and provide your valuable comments.
>> 
>> 
>> 
>> Thanks,
>> Swati Sharma
>> Runtime Software Development Engineer 
>> Intel
>
> Swati Sharma has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8271195: Review comments resolved.

Test is still failing on aarch64. I really encourage you to consider doing a simpler approach like the one I've suggested instead of storing the page sizes as index in an array. I find the current version hard to debug and I don't really see any benefit of the array compared to a list that can be sorted to get decreasing order.

Below is the output from the failure, I've removed a lot. Looks strange to run the test with `LargePageSizeInBytes=0K`, so I expect an unexpected value has been added to the array: 

No Pages configured for 16777216kB
No Pages configured for 2048kB
No Pages configured for 524288kB
Command line: [ ... -Xlog:pagesize -XX:LargePageSizeInBytes=0K -XX:+UseParallelGC -XX:+UseLargePages -Xmx2g -Xms1g -version ]
...
Checking allocation for 64K
[0.001s][info][pagesize] Using the default large page size: 512M
[0.001s][info][pagesize] Usable page sizes: 64k, 2M, 512M
[0.001s][info][pagesize] Large page size (512M) failed sanity check, checking if smaller large page sizes are usable
[0.002s][warning][pagesize] UseLargePages disabled, no large pages configured and available on the system.
[0.003s][info   ][pagesize] CodeHeap 'non-nmethods':  min=2496K max=5760K base=0x0000fffea55d0000 page_size=64K size=5760K
[0.012s][info   ][pagesize] CodeHeap 'profiled nmethods':  min=2496K max=120000K base=0x0000fffea5b70000 page_size=64K size=120000K
[0.022s][info   ][pagesize] CodeHeap 'non-profiled nmethods':  min=2496K max=120000K base=0x0000fffead0a0000 page_size=64K size=120000K
[0.032s][info   ][pagesize] Heap:  min=1G max=2G base=0x0000000080000000 page_size=64K size=2G
TestCase Passed for pagesize: 0K, allocated pagesize:64K
----------System.err:(14/802)----------
java.lang.AssertionError: nullTestCase Failed for 0K page allocation

	at runtime.os.TestExplicitPageAllocation.testCase(TestExplicitPageAllocation.java:189)
	at runtime.os.TestExplicitPageAllocation.main(TestExplicitPageAllocation.java:82)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:577)
	at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
	at java.base/java.lang.Thread.run(Thread.java:828)

JavaTest Message: Test threw exception: java.lang.AssertionError: nullTestCase Failed for 0K page allocation

JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.AssertionError: nullTestCase Failed for 0K page allocation

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

PR: https://git.openjdk.java.net/jdk/pull/7326