RFR: 8219414: SA: jhsdb jsnap throws UnmappedAddressException with core generated by gcore

[Chris Plummer]

Ok. The changes look fine to me then.

thanks,

Chris

On 2/20/19 6:02 PM, Yasumasa Suenaga wrote:
> Hi Chris,
>
> I grep'ed with "MAP_SHARED" on jdk/src.
> Shared memory is used in ZGC (ZBackingFile and ZPhysicalMemoryBacking)
> and in FileChannel::map at least.
>
> I think we have memory footprint concern about them, but shared memory
> should be dumped.
> If we did not get them, we cannot analyze ZGC related behavior and
> other code which uses shared memory.
> (We can pass FD to os::reserve_memory - it will use shared memory if
> FD is passed.)
>
> Thus I want to introduce `DumpSharedMappingsInCore` for dumping shared
> memory and set it to true by default.
>
>
> Thanks,
>
> Yasumasa
>
>
> 2019年2月21日(木) 3:10 Chris Plummer <chris.plummer at oracle.com>:
>> [adding runtime]
>>
>> Hi Yasumasa,
>>
>> Overall looks good. Just a couple of questions.
>>
>> Do we have the same footprint concerns with the shared mappings as we
>> did with the private mappings? If not, possibly it doesn't need an
>> option and should always be enabled.
>>
>> thanks,
>>
>> Chris
>>
>> On 2/20/19 12:03 AM, Yasumasa Suenaga wrote:
>>> Hi all,
>>>
>>> Please review this webrev:
>>>
>>>     JBS: https://bugs.openjdk.java.net/browse/JDK-8219414
>>>     webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8219414/webrev.00/
>>>
>>> I tried to get PerfCounter values via `jhsdb jsnap` from core image
>>> which is generated by `gcore` (provided by GDB), but I encountered
>>> UnmappedAddressException.
>>>
>>> It is caused by `generate-core-file` on GDB regards `coredump_filter` on procfs.
>>>
>>>     https://sourceware.org/gdb/onlinedocs/gdb/Core-File-Generation.html
>>>
>>> JDK-8200613 introduced `DumpPrivateMappingsInCore` for CDS. I want to
>>> introduce `DumpSharedMappingsInCore` for shared memory mapping.
>>>
>>> Currently `DumpPrivateMappingsInCore` affects when `UseSharedSpaces` is enabled.
>>> I want `DumpPrivateMappingsInCore` to affect independently in this
>>> change because file-backed private memory which is not CDS might be
>>> useful in the future.
>>>
>>>
>>> Thanks,
>>>
>>> Yasumasa
>>