Path: utzoo!attcan!ncrcan!scocan!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: vfork (was Re: Paging page tables)
Message-ID: <1990Jul12.153700.15756@sco.COM>
Date: 12 Jul 90 19:37:00 GMT
References: <920@dgis.dtic.dla.mil> <5830@titcce.cc.titech.ac.jp> <1990Jul11.191235.8117@cs.rochester.edu> <269B8E4F.27941@ics.uci.edu> <5845@titcce.cc.titech.ac.jp>
Reply-To: seanf@opus.UUCP (Sean Fagan)
Followup-To: comp.unix.wizards
Organization: The Santa Cruz Operation, Inc.
Lines: 18

[Note the followup...]
In article <5845@titcce.cc.titech.ac.jp> mohta@necom830.cc.titech.ac.jp (Masataka Ohta) writes:
>If there is only 100MB swap space, and a 80MB process want to fork
>just to exec a small program such as shell, 160MB of swap space must
>be temporarily allocated. It is impossible.

Since when?  SysV doesn't do that.  The swap space is allocated *on demand*,
not on fork.  Since the data pages are marked COW, only if they are written
is swap space needed.  If you can get away with not writing to anything,
including your stack, then no extra swap space is used *at all*.

So I guess it's not so impossible after all, is it?

-- 
-----------------+
Sean Eric Fagan  | "Just think, IBM and DEC in the same room, 
seanf@sco.COM    |      and we did it."
uunet!sco!seanf  |         -- Ken Thompson, quoted by Dennis Ritchie