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Date: Fri, 31 Jan 1997 11:33:22 +0900 (JST)
From: Michael Hancock <michaelh@cet.co.jp>
To: Martin Cracauer <cracauer@wavehh.hanse.de>
cc: rminnich@Sarnoff.COM, freebsd-hackers@FreeBSD.ORG
Subject: Re: Using rfork() / threads
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On Thu, 30 Jan 1997, Martin Cracauer wrote:

> rminnich@Sarnoff.COM (Ron G. Minnich) wrote:
> 
> [rfork]
> 
> >VM space handling is a little different. If you request VM space sharing,
> >you don't exactly get Vm address space sharing:  what you get is instead
> >shared data areas where in normal fork they are copied. More details on 
> >request. The effect is what you want, though: shared data areas. 
> 
> Could you explain a bit more. What exactly is the difference between
> VM space sharing and shared data areas from the process' and the
> kernel perspective?

In fork the mappings are copied and the data is marked copied on write. 
In the original vfork you just inherited the mappings (Vm address space
sharing).  In rfork the mappings are copied but the data is not marked
copy on write.  I haven't analyzed rfork so someone might correct me but
this makes sense to me.

Regards,


Mike