[Rd] SUGGESTION: Settings to disable forked processing in R, e.g. parallel::mclapply()

Tomas Kalibera tom@@@k@||ber@ @end|ng |rom gm@||@com
Mon Apr 15 12:12:40 CEST 2019

On 4/15/19 11:02 AM, Iñaki Ucar wrote:
> On Mon, 15 Apr 2019 at 08:44, Tomas Kalibera <tomas.kalibera using gmail.com> wrote:
>> On 4/13/19 12:05 PM, Iñaki Ucar wrote:
>>> On Sat, 13 Apr 2019 at 03:51, Kevin Ushey <kevinushey using gmail.com> wrote:
>>>> I think it's worth saying that mclapply() works as documented
>>> Mostly, yes. But it says nothing about fork's copy-on-write and memory
>>> overcommitment, and that this means that it may work nicely or fail
>>> spectacularly depending on whether, e.g., you operate on a long
>>> vector.
>> R cannot possibly replicate documentation of the underlying operating
>> systems. It clearly says that fork() is used and readers who may not
>> know what fork() is need to learn it from external sources.
>> Copy-on-write is an elementary property of fork().
> Just to be precise, copy-on-write is an optimization widely deployed
> in most modern *nixes, particularly for the architectures in which R
> usually runs. But it is not an elementary property; it is not even
> possible without an MMU.

Yes, old Unix systems without virtual memory had fork eagerly copying. 
Not relevant today, and certainly not for systems that run R, but indeed 
people interested in OS internals can look elsewhere for more precise 


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