[External] : Re: ReplayCompiles as non-develop switch ?

[Vladimir Kozlov]

I agree that it is useful.

Thanks,
Vladimir K

On 8/18/22 6:22 PM, dean.long at oracle.com wrote:
> This does sounds like a useful feature.  I was surprised to find out while investigating JDK-8291665 that compiler node 
> limits don't seem to be enforced in product builds.
> 
> dl
> 
> On 8/18/22 2:43 AM, Thomas Stüfe wrote:
>> (offlist)
>>
>> Just wanted your opinion on something.
>>
>> I prepared https://github.com/openjdk/jdk/pull/9891 <https://github.com/openjdk/jdk/pull/9891>, which adds NMT malloc 
>> limits (VM will fatal out if more than x was allocated), and these limits can also be category-specific. That way one 
>> could call the VM with -XX:MallocLimit=compiler:250M and if the compiler malloc load - which is typically mostly Arena 
>> - hits 250M we get a fatal error and a replay file. Note it won't count code heap since that is mmap.
>>
>> I originally did this to simplify analysis in situations like https://bugs.openjdk.org/browse/JDK-8291665 
>> <https://bugs.openjdk.org/browse/JDK-8291665>, where we have a release VM and the compiler arena balloons. But we also 
>> could use this for other things.
>>
>> 1) for automatic memory bounds checks on all compiler jtreg tests. If we can agree on what a reasonable upper ceiling 
>> would be for Compiler malloc usage, then we could set this limit for all tests wholesale. If we have a case where a 
>> compiler test uses too much memory, we now get a test error. Of course, in cases where a compiler loop causes an 
>> unbound memory raise we get a test error today too, just faster and possibly without OOM kill.
>>
>> 2) We also could use it as replacement of the -XX:CiCrashAt mechanism, at least in parts of the tests: set compile 
>> arena very low and start compiler, you get an assert and a replay file.
>>
>> What do you think, is this worthwhile? (especially (1))
>>
>> Cheers, Thomas
>>
>>
>> On Wed, Aug 17, 2022 at 8:04 PM Vladimir Kozlov <vladimir.kozlov at oracle.com <mailto:vladimir.kozlov at oracle.com>> wrote:
>>
>>     On 8/16/22 9:01 PM, Thomas Stüfe wrote:
>>      > On Tue, Aug 16, 2022 at 9:00 PM Vladimir Kozlov
>>     <vladimir.kozlov at oracle.com <mailto:vladimir.kozlov at oracle.com>
>>     <mailto:vladimir.kozlov at oracle.com
>>     <mailto:vladimir.kozlov at oracle.com>>> wrote:
>>      >
>>      >     On 8/16/22 10:05 AM, Thomas Stüfe wrote:
>>      >      > Hi,
>>      >      >
>>      >      > Is there a particular reason why ReplayCompiles needs to
>>     be a develop switch? Or was it just not considered useful
>>      >      > without asserts?
>>      >
>>      >     It replays compilation which we want to debug in debug VM.
>>     Why do you want it be `product` flag?
>>      >
>>      >     We have DumpReplayDataOnError product flag to dump compiler
>>     replay data from product VM:
>>      >
>>     https://github.com/openjdk/jdk/blob/master/src/hotspot/share/compiler/compiler_globals.hpp#L331
>>     <https://github.com/openjdk/jdk/blob/master/src/hotspot/share/compiler/compiler_globals.hpp#L331>
>>      >      
>>  <https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/master/src/hotspot/share/compiler/compiler_globals.hpp*L331__;Iw!!ACWV5N9M2RV99hQ!JRgjhoZKOMvpjeekz0FN5_oc8OR6PZp-lDqLr7W_AEpu5wV0xtVtbCvvgD_XWCIeoqN88QPk0i9nNBU6w2OexzZiW4G-$ 
>> <https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/master/src/hotspot/share/compiler/compiler_globals.hpp*L331__;Iw!!ACWV5N9M2RV99hQ!JRgjhoZKOMvpjeekz0FN5_oc8OR6PZp-lDqLr7W_AEpu5wV0xtVtbCvvgD_XWCIeoqN88QPk0i9nNBU6w2OexzZiW4G-$>> 
>>
>>      >
>>      >
>>      > Hi Vladimir,
>>      >
>>      > to reproduce a compiler error in a release VM.
>>      >
>>      > - to experiment what its effect is on a VM that was actually
>>     shipped to customers, without using a debug VM and
>>      > switching tens of asserts off. E.g., in the case of
>>     https://bugs.openjdk.org/browse/JDK-8291665
>>     <https://bugs.openjdk.org/browse/JDK-8291665>
>>      > <https://bugs.openjdk.org/browse/JDK-8291665
>>     <https://bugs.openjdk.org/browse/JDK-8291665>>, how steep and how
>>     quickly RSS raises, and whether the raise limits itself
>>      > or is infinite.
>>      > - to see whether a certain build of a shipped VM is actually
>>     affected by a certain bug. Not every bug surfaces in every
>>      > build.
>>      >
>>      > None of that are very hard reasons, and these situations are
>>     rare. But they do occur, and it would be a bit more
>>      > convenient to have this switch.
>>
>>     So you want it for verification purpose and not for debugging an
>>     issue. We did not consider it when implemented.
>>     I agree it could be useful and it is not hard to convert
>>     ReplayCompiles to diagnostic flag.
>>     It will increase VM size but not much.
>>
>>     File RFE.
>>
>>     Thanks,
>>     Vladimir K
>>
>>      >
>>      > Cheers, Thomas
>>      >
>>      >
>>