[erlang-questions] halfword emulator state

Paolo Negri <>
Mon May 30 22:20:42 CEST 2011

Dear list

I would like to assess the state of development and recommended usage
of the halfword emulator.

Apart from the initial announcement [1] and the fixes/improvements
introduced with R14B03 [2] there hasn't been much discussion about it.
As we're evaluating the use of the halfword emulator in production I
would like to ask questions.

- Is anyone already using the halfword emulator in production
environments, if yes, are what are the experiences, is it stable, what
are the effective gains, is there any measurable overhead?

- Can the halfword emulator be considered suitable and stable for
production usage as the distribution of which is part?

- [2] states: "Much more of internal memory structures have been made
able to use "high" memory and are no longer restricted to the 4Gb
limit that still applies for all process heap data."
  Is there any documentation explaining exactly which structures can
use the high memory and what instead is constrained to the "low"
memory? Where would the content of the constant pool reside?

- How could the containment of structures restricted to the "low"
memory be measured? How would someone monitor the memory usage of the
VM being able to prevent out of memory errors without restricting the
whole VM to use over 4Gb?

- What are the caveats - if any - for using nifs when using the
halfword emulator? Which aspects of the nifs should be tested in order
to consider safe to run them with the halfword emulator?

[1] http://www.erlang.org/download/otp_src_R14B02.readme
[2] http://www.erlang.org/download/otp_src_R14B03.readme

Thanks for releasing the halfword emulator and thanks in advance for
your answers.


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