RFR: 8246135: ZGC: Save important log lines and print them when dumping hs_err files

[Per Liden]

Looks good!

/Per

On 6/2/20 3:51 PM, Stefan Karlsson wrote:
> Hi all,
> 
> While working on getting more information when dumping early during 
> initialization, it became apparent that we don't print these log lines 
> as early as we could. In ZGC we can assert and/or fail during the set up 
> of the heap. I'd like to print the precious lines even when that 
> happens. The following patch moves the the precious line printing out of 
> ZCollectedHeap and into a direct call from the VMError code. GCs that 
> populate these lines will now automatically get them printed.
> 
> https://cr.openjdk.java.net/~stefank/8246135/webrev.04.delta
> https://cr.openjdk.java.net/~stefank/8246135/webrev.04
> 
> Thanks,
> StefanK
> 
> On 2020-05-29 12:23, Stefan Karlsson wrote:
>> Hi all,
>>
>> Please review this patch to save some of the important ZGC log lines 
>> and print them when dumping hs_err files.
>>
>> https://cr.openjdk.java.net/~stefank/8246135/webrev.01/
>> https://bugs.openjdk.java.net/browse/JDK-8246135
>>
>> The patch adds a concept of "precious" log lines. What's typically 
>> logged are GC initialization lines, but also error messages are saved. 
>> These lines are then dumped in the hs_err file if the JVM crashes or 
>> hits an assert. The lines can also be printed in a debugger to get a 
>> quick overview when debugging.
>>
>> The precious lines are always saved, but just like any other Unified 
>> Logging calls, only logged if the tags are enabled.
>>
>> The patch builds on the JDK-8246134 patch. The hs_err output looks 
>> like this:
>>
>> ZGC Precious Log:
>>  NUMA Support: Disabled
>>  CPUs: 8 total, 8 available
>>  Memory: 16384M
>>  Large Page Support: Disabled
>>  Medium Page Size: 32M
>>  Workers: 5 parallel, 1 concurrent
>>  Address Space Type: Contiguous/Unrestricted/Complete
>>  Address Space Size: 65536M x 3 = 196608M
>>  Min Capacity: 42M
>>  Initial Capacity: 256M
>>  Max Capacity: 4096M
>>  Max Reserve: 42M
>>  Pre-touch: Disabled
>>  Uncommit: Enabled
>>  Uncommit Delay: 300s
>>  Runtime Workers: 5 parallel
>>
>> ZGC Globals:
>>  GlobalPhase:       2 (Relocate)
>>  GlobalSeqNum:      1
>>  Offset Max:        4096G (0x0000040000000000)
>>  Page Size Small:   2M
>>  Page Size Medium:  32M
>>
>> ZGC Metadata Bits:
>>  Good:              0x0000100000000000
>>  Bad:               0x00002c0000000000
>>  WeakBad:           0x00000c0000000000
>>  Marked:            0x0000040000000000
>>  Remapped:          0x0000100000000000
>>
>> Heap:
>>  ZHeap           used 12M, capacity 256M, max capacity 4096M
>>  Metaspace       used 6501K, capacity 6615K, committed 6784K, reserved 
>> 1056768K
>>   class space    used 559K, capacity 588K, committed 640K, reserved 
>> 1048576K
>>
>> ZGC Page Table:
>>  Small   0x0000000000000000 0x0000000000200000 0x0000000000200000 
>> Allocating
>>  Small   0x0000000000200000 0x0000000000240000 0x0000000000400000 
>> Allocating
>>  Small   0x0000000000400000 0x0000000000600000 0x0000000000600000 
>> Allocating
>>  Small   0x0000000000600000 0x0000000000800000 0x0000000000800000 
>> Allocating
>>  Small   0x0000000000800000 0x00000000009c0000 0x0000000000a00000 
>> Allocating
>>  Small   0x0000000000a00000 0x0000000000a40000 0x0000000000c00000 
>> Allocating
>>
>> Thanks,
>> StefanK
>