RFR: 8207851 JEP Draft: Support ByteBuffer mapped over non-volatile memory

Andrew Dinn adinn at redhat.com
Fri Jul 20 13:50:22 UTC 2018

I have finally managed to draft a JEP to formally present the proposal I
circulated a month or two back regarding support for MappedByteBuffer
access to non-volatile memory.


The JEP references a re-implementation of the proposed API:


The rework addresses some of the feedback provided in the initial

Previous Thread:
  (starts in May archive)
(continues into June archive at)

In particular, the re-implementation has split the original Hotspot
intrinsic used to guarantee writeback an address range into 3 intrinsics
relocated into class Unsafe which

  write back a single cache line
  perform any necessary memory sync pre-writeback
  perform any necessary memory sync post-writeback

Also, the implementation has been extended from Linux on x86_64 to also
coater for Linux on AArch64. The latter version compiles and generates
correct code but has not yet been tested because I have not yet obtained
access to a box with a suitably up to date kernel.

Comments and suggestions for improvement would be very welcome.

n.v. Jonathan Halliday is about to get his hands on an x86 box with a
real NVM dimm so we may soon be able to try this out with NVM proper
rather than testing with volatile memory pretending to be NVM.


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander

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