[erlang-questions] Garbage collection

[Lukas Larsson]

On Fri, Oct 31, 2014 at 10:51 AM, Chandru <
chandrashekhar.mullaparthi@REDACTED> wrote:

> Thank you Lukas.
>
> On 31 October 2014 09:37, Lukas Larsson <lukas@REDACTED> wrote:
>
>> Hello,
>>
>> On Fri, Oct 31, 2014 at 10:20 AM, Chandrashekhar Mullaparthi <
>> chandrashekhar.mullaparthi@REDACTED> wrote:
>>
>>>
>>>
>>> I have a question about beam’s GC implementation. When an erlang process
>>> is being GCed, is the processing required to do the GC taken out of the
>>> process’s 2000 reduction quota, or is it done after a process has been
>>> scheduled out?
>>>
>>>
>>>
>>
>> The GC work is taken out of the process' reductions. The GC is never
>> triggered when it is scheduled out, but it can be triggered before being
>> scheduled in, in which case the newly allotted reductions will be reduced
>> by the GC work.
>>
>
> So what happens if the process has a large heap? Can the GC end up taking
> more time than to execute 2000 reductions? Or is it somehow time bounded?
> If it is not time bounded, it explains a lot of the problems I'm seeing on
> a system.
>

The current GC is not incremental, so once it has started doing work it
cannot be interrupted. This means that if a process has a large heap it
will block all other execution on that scheduler for the GC duration.
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