RFR: JDK-8317683: Add JIT memory statistics [v5]

[Brice Dutheil]

On Fri, 13 Oct 2023 10:15:37 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> This proposal adds a way to monitor C1/C2 memory usage per compilation. 
>> 
>> We are flying a bit blind there: NMT is okay for initial triaging but no help when digging deeper into compiler footprint. NMT shows how much native memory the JIT uses but lumps together footprints from concurrent compilations, making its peak values arbitrary. And we have no way to associate the NMT numbers with individual allocations.
>> 
>> The statistic added by this patch shows footprint *per compilation*. It measures memory spikes per thread for a single compilation. It then presents them with additional information, e.g., the node count (for C2). 
>> 
>> Example printout:
>> 
>> 
>> 112703:
>> Compilation memory statistics
>> 
>> Legend:
>>   total  : memory allocated via arenas while compiling
>>   NA     : ...how much in node arenas (if c2)
>>   RA     : ...how much in resource areas
>>   #nodes : ...how many nodes (if c2)
>>   time   : time of last compilation (sec)
>>   type   : compiler type
>>   #rc    : how often recompiled
>>   thread : compiler thread
>> 
>> total     NA        RA        #nodes  time    type  #rc thread              method
>> 30273336  6383040   18027000  18257   1,979   c2    2   0x00007f6f0c136460  java/lang/ClassLoader.loadClass((Ljava/lang/String;)Ljava/lang/Class;) 
>> 27690456  5892160   16211800  15179   3,643   c2    2   0x00007f6f0c0433e0  org/springframework/cache/interceptor/CacheOperationSourcePointcut.matches((Ljava/lang/reflect/Method;Ljava/lang/Class;)Z) 
>> ...
>> ...
>> 
>> 
>> [full example printout here](https://github.com/openjdk/jdk/files/12853477/compiler-statistic-petclinic.txt)
>> 
>> #### Usage
>> 
>> The statistic needs to be enabled with a new compile command (`-XX:CompileCommand="CollectMemStat,*.*` or `-XX:CompileCommand="PrintMemStat,*.*"`). 
>> 
>> It then can be printed with a new jcmd: `jcmd xxx Compiler.memory`.
>> 
>> `PrintMemStat` also prints the usage out after compilation and again, as sorted table, at VM shutdown.
>> 
>> #### Technical details
>> 
>> The patch exploits the fact that compilers use arenas almost exclusively. It hooks into `Arena::grow()` to track allocations. That makes memory tracking very cheap at an acceptable loss in fidelity (we only track arena chunk allocations, not individual Arena allocations).
>> 
>> Peak values are tracked per compiler thread. That works since all arenas used during compilation are associated with a compiler thread and never change that association during the compilation.
>> 
>> We measure total footprint...
>
> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Change to single option MemStat
>  - Merge branch 'master' into arena-per-thread-stats-for-compiler
>  - Feedback Andrew
>  - remove stray newlines
>  - MemStat->CollectMemStat
>  - Feedback Vladimir
>  - Compilation memory statistic

> anon mappings were unnamed

> this type of investigation workflow:
> 
> * there is a report of increased RSS
> * we check first the `pmap -X` output to find if C1/C2 compiler threads anon mappings and diff them from the good version
> * if we have an increase there we go down into the rabbit hole with the JIT statistics you provided

I can relate to that in more ways than only compiler threads. 

Using `prctl` / `PR_SET_VMA_ANON_NAME` approach looks interesting though albeit unavailable on other than Linux. I never used this mechanism before but using this may imply possible issues with glibc's ability to merge adjacent VMAs ; could it be avoided if the name is the "same", i.e. making `malloc` use the the same mmaped area under the hood and reported as such in `pamp -X`.

_Note: This is just exposing unproven ideas at this point, maybe opening ticket makes more sense to discuss this if the idea is indeed interesting / doable._

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PR Comment: https://git.openjdk.org/jdk/pull/16076#issuecomment-1761709688