[erlang-questions] Fwd: Maximising memory compactness

Andreas Schumacher <>
Fri Apr 4 17:26:01 CEST 2014


Honestly, we did not measure the number of users, but we made a rough guess
based on the questions, comments, and/or bug reports we got for the
half-word emulator.

Andreas

-----Original Message-----
From: Tuncer Ayaz [mailto:]
Sent: den 4 april 2014 14:25
To: Andreas Schumacher
Cc: ; Olivier BOUDEVILLE
Subject: Re: [erlang-questions] Fwd: FW: Maximising memory compactness

On Fri, Apr 4, 2014 at 1:33 PM, Andreas Schumacher wrote:
> As a matter of fact, the half-word emulator will be deprecated in OTP
> 17.0, which will be released next week. The reason for that is that
> there have been very few (if any) users; and thus, the maintenance
> costs outweigh its value.

FWIW, I use it. But more importantly, how did you measure the number of
users? For comparison, JVM's compressed oops has been default enabled for a
long time, but to be precise it's not _exactly_ the same thing.

http://docs.oracle.com/javase/7/docs/technotes/guides/vm/performance-enhancements-7.html
"Compressed oops is supported and enabled by default in Java SE 6u23 and
later. In Java SE 7, use of compressed oops is the default for 64-bit JVM
processes when -Xmx isn't specified and for values of -Xmx less than 32
gigabytes."

https://wikis.oracle.com/display/HotSpotInternals/CompressedOops

That said, what about implementing x32 ABI support as an alternative?
As far as I can tell this would have to be explicitly implemented in HiPE
too.

> -----Original Message-----
> From: 
> [mailto:] On Behalf Of Kostis
> Sagonas
> Sent: den 4 april 2014 11:39
> To: Erlang
> Subject: Re: [erlang-questions] Maximising memory compactness
>
> On 04/04/2014 10:33 AM, Olivier BOUDEVILLE wrote:
>> Let's suppose one would like to run a large, distributed (Erlang)
>> application, with many processes, and that ends up, in some cases,
>> being RAM-bound.
>  > ...
>> The half-word emulator would seem the simplest/most elegant solution
>> to do so ....
>  >
>> So, my question: would relying on a set of 32-bit VMs per host,
>> instead of a single 64-bit VM, look like the best option here?
>
> My opinion is (and has always been) that the half-word emulator seems
> cute on the surface but deep down is a bad idea (esp. for a language
> with automatic memory management like Erlang, or if your application
> has any plans of growing someday).
>
> So I would really advice against it. In fact, IMO it's better to try
> to forget about its existence for anything other than for small
> embedded devices or in machines that do not have more than 3GB of
> memory.
>
> Unfortunately, I am very busy to elaborate more on this right now.
> But even if I had more time, I would probably try to find better
> things to do than think/talk about the half-word emulator. Leaning
> back and relax until you forget about it (or simply waiting for the
> day that it is taken out of the distribution) is preferable IMO.
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