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From: jrvalverde@samba.cnb.uam.es (jr)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Linux vs. FreeBSD ... (FreeBSD extremely mem/swap hungry)
Date: Tue, 28 May 1996 14:58:43 +0100
Organization: Centro Nacional de Biotecnologia
Lines: 45
Message-ID: <jrvalverde-2805961458430001@b12mc6.cnb.uam.es>
References: <3188C1E2.45AE@onramp.net> <4o3ftc$4rc@zot.io.org> <31A5A8F6.15FB7483@zeus.co.uk> <31A5D0A8.59E2B600@zeus.co.uk> <4oca4b$1gm@keltia.freenix.fr>
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In article <4oca4b$1gm@keltia.freenix.fr>, roberto@keltia.freenix.fr
(Ollivier Robert) wrote:
>
> The VM subsystem in Linux and FreeBSD are very different although I think
> Linux recently got an unified VM/buffer cache like we do since post 2.0. It
> is true that FreeBSD needs more swap than Linux ; it is an artifact from
> the VM system. I also think that our VM system is more advanced but I
> haven't compared line by line.
>
> Regards,
> --
> Ollivier ROBERT -=- FreeBSD: The daemon is FREE! -=- roberto@freebsd.org
> -=-=-=-=-=-=-=-=-=-=- FreeBSD 2.x FAQ maintainer -=-=-=-=-=-=-=-=-=-=-=-=-
If this can help, I have had some problems with my computer recently. In
trying to find the cause I wrote a program to test memory access...
The program allocates memory, fills it with random data (to ensure
allocation) reserving memory up to a small space of swap (to ensure all
RAM is reserved). Then it verifies the contents of RAM pages (a bit less
than the available RAM, to avoid swap space) several times.
When run under FreeBSD the first test pass took about half a minute,
and the rest where blazingly fast. That's because the first pass has to
restore the working set from swap...
Under Linux the first pass also takes longer, but this time, it's about
15 minutes.
I take this to mean that Linux uses a strict LRU algorithm, so
when cycling access to big memory chunks (bigger than RAM) it takes too
long. Under FreeBSD the VM system answers better. There are -obviously-
differences.
That is to say: both VM systems are different, and each one will surely
behave better under one or other circumstances. There's not much sense in
bashing any of them in general as seen in these threads. There could be in
stating that for some given purpose or another and under some specific
circumstances, one solution may behave better or worst. And nothing more.
To cut it short: critics of 'the general case' are stupid loser behavior.
One has to know the pros- and cons- of every tool and be able to decide
which is best suited for each specific application and use it.
jr