[11] RFR(S): 8205499: C1 temporary code buffers are not removed with -XX:+UseDynamicNumberOfCompilerThreads

[Nils Eliasson]

Nice catch!

Looks good.

// Nils


On 2018-06-28 12:39, Tobias Hartmann wrote:
> Hi,
>
> please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8205499
> http://cr.openjdk.java.net/~thartmann/8205499/webrev.00/
>
> The problem is that with -XX:+UseDynamicNumberOfCompilerThreads, compiler threads are dynamically
> created and removed but the C1 temporary code buffers are not deallocated. As a result, the code
> cache fills up with long running applications, disabling compilation.
>
> I was able to reproduce this by slightly modifying the code such that compiler threads are
> aggressively added and removed. The code cache quickly fills up and we get the expected warning [1].
> I was not able to create a stable regression test because that would require to alternate between
> generating compilation tasks and waiting for compiler threads to become idle and get removed (i.e.,
> the test would be long running).
>
> The fix is to deallocate the code buffers in the thread destructor. I've verified that this solves
> the issue.
>
> Thanks,
> Tobias
>
> [1] Java HotSpot(TM) 64-Bit Server VM warning: CodeCache is full. Compiler has been disabled.
> Java HotSpot(TM) 64-Bit Server VM warning: Try increasing the code cache size using
> -XX:ReservedCodeCacheSize=
> CodeCache: size=51200Kb used=50978Kb max_used=50990Kb free=221Kb
>   bounds [0x00007fd068e00000, 0x00007fd06c000000, 0x00007fd06c000000]
>   total_blobs=1284 nmethods=237 adapters=787
>   compilation: disabled (not enough contiguous free space left)
>                stopped_count=1, restarted_count=0
>   full_count=0
> Java HotSpot(TM) 64-Bit Server VM warning: Initialization of C1 CompilerThread3 thread failed (no
> space to run compilers)
> Java HotSpot(TM) 64-Bit Server VM warning: Initialization of C1 CompilerThread5 thread failed (no
> space to run compilers)
> Java HotSpot(TM) 64-Bit Server VM warning: Initialization of C1 CompilerThread4 thread failed (no
> space to run compilers)