RFR(M): 8171181: Supporting heap allocation on alternative memory devices

[David Holmes]

Hi Kishor,

I took a quick look at this and have a few initial comments ... but 
overall it looks pretty straight-forward.

On 28/02/2017 9:52 AM, Kharbas, Kishor wrote:
> Hello all!
> I have proposed a JEP to support allocation of Java heap on new memory devices such as NV-DIMMs like Intel's 3D XPoint.
> Such a feature has applications in multi-JVM deployments, big data applications and in-memory databases.
> Please find the details here - https://bugs.openjdk.java.net/browse/JDK-8171181 and the patch for the implementation is at http://cr.openjdk.java.net/~kkharbas/8153327_webrev.04
> I would appreciate a review and feedback from the community for this JEP.

Is there something linux specific about the implementation? If not it 
should be in os_posix.cpp and be usable by all the POSIX compliant OS.

In os::create_file_for_heap:

  - you need to use the per-thread signal masking function, 
pthread_sigmask, not sigprocmask. Also you need restore the signal mask 
before the error return of -1
  - you can't use umask as that might impact files concurrently created 
by other code in the VM. I expect you will need to create it then fchmod it.
  - the warning should include the reason for the failure. Though it is 
unclear whether this should be a warning or a fatal error.
  - check returns codes from library calls - add assertions that they 
succeed if they should be "impossible" to fail. Though I think perhaps 
an unlink failure may need to be anticipated.

In os::map_memory_to_file:
  - report reasons for failure explicitly
  - do not assign posix_fallocate to errno!

The err_msg function is used for printf-style formatting, so you don't 
need it for simple string messages. But in some cases your messages 
should also include strerror output when there are failures.

Some tests will also be needed of course.

Thanks,
David

> Thank you!
> Kishor
>