*BSD News Article 27911


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From: moore@cs.utk.edu (Keith Moore)
Newsgroups: comp.os.386bsd.development
Subject: Re: Notes on the *new* FreeBSD V1.1 VM system
Date: 1 Mar 1994 03:46:00 GMT
Organization: Univ. of Tenn. Computer Science, Knoxville
Lines: 23
Distribution: world
Message-ID: <2kudpoINNbhd@CS.UTK.EDU>
References: <BcxpGux.dysonj@delphi.com> <2ke3ss$l0d@u.cc.utah.edu> <Ja4p+zR.dysonj@delphi.com> <2kfcur$dd1@germany.eu.net> <2kgdcd$mls@usenet.pa.dec.com> <2kkqib$h2h@Germany.EU.net> <CLutBp.4K9@flatlin.ka.sub.org> <RA0Jn4G.dysonj@delphi.com>
Reply-To: moore@cs.utk.edu
NNTP-Posting-Host: wilma.cs.utk.edu

In article <RA0Jn4G.dysonj@delphi.com>, John Dyson <dysonj@delphi.com> writes:
> Christoph Badura <bad@flatlin.ka.sub.org> writes:
>  
> >Getting it right means, not overcommiting VM and not killing random
> >processes.

Damn straight.  Let's not have FreeBSD go the way of AIX.

I don't think this is that hard...all you need is a count of the
number of unallocated pages of swap space.  When someone allocates
more pages, you decrement the count; if there's not enough room, fail.
When pages are freed, you add them back to the available page count.
The performance impact is minimal except perhaps on multiprocessor
systems where you have to get exclusive access to the counter.

You can still wait until you get a fault on the new page (and need to
find a place to put the data that was there) before finding where it
goes on the disk.

--
Keith Moore / U.Tenn CS Dept / 107 Ayres Hall / Knoxville TN  37996-1301
Internet: moore@cs.utk.edu      BITNET: moore@utkvx
Preserve the fourth amendment!  Say HELL NO to key escrow!