Date: Fri, 15 Oct 2004 13:49:48 +0100 From: David Malone <dwmalone@maths.tcd.ie> To: Oliver Fromme <olli@lurza.secnetix.de> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: NFS + VM question Message-ID: <20041015124948.GA66898@walton.maths.tcd.ie> In-Reply-To: <200410141427.i9EERcTF056740@lurza.secnetix.de> References: <200410141427.i9EERcTF056740@lurza.secnetix.de>
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On Thu, Oct 14, 2004 at 04:27:38PM +0200, Oliver Fromme wrote:
> On the other hand, the kernel should know that the mounts
> come from the same NFS source, so it might actually be able
> to handle it efficiently (i.e. share). But I really don't
> know. Any FreeBSD kernel hacker can enlighten me?
Since the server could actually hand out different content depending
on the mount instance, I don't think the NFS client could make these
assumptions. If you try NFS mounting /usr a few times and then time
how long it takes to cat a cached file, you'll see this.
> If the memory isn't shared in this situation, is there a
> way to change the design so it can be shared? chroot and
> NFS are "musts", though.
I don't think there is an easy way to get this caching to happen,
short of using hard links or some kind of union mount instead of
NFS.
David.
> /usr/bin/time cat /usr/X11R6/bin/Xvfb > /dev/null
0.17 real 0.00 user 0.03 sys
> /usr/bin/time cat /usr/X11R6/bin/Xvfb > /dev/null
0.02 real 0.00 user 0.02 sys
> /usr/bin/time cat /usr/X11R6/bin/Xvfb > /dev/null
0.02 real 0.00 user 0.02 sys
> /usr/bin/time cat /mnt1/X11R6/bin/Xvfb > /dev/null
0.21 real 0.00 user 0.04 sys
> /usr/bin/time cat /mnt1/X11R6/bin/Xvfb > /dev/null
0.03 real 0.00 user 0.03 sys
> /usr/bin/time cat /mnt1/X11R6/bin/Xvfb > /dev/null
0.03 real 0.00 user 0.02 sys
> /usr/bin/time cat /mnt2/X11R6/bin/Xvfb > /dev/null
0.21 real 0.00 user 0.04 sys
> /usr/bin/time cat /mnt2/X11R6/bin/Xvfb > /dev/null
0.03 real 0.00 user 0.03 sys
> /usr/bin/time cat /mnt2/X11R6/bin/Xvfb > /dev/null
0.03 real 0.00 user 0.03 sys
> /usr/bin/time cat /mnt3/X11R6/bin/Xvfb > /dev/null
0.21 real 0.00 user 0.04 sys
> /usr/bin/time cat /mnt3/X11R6/bin/Xvfb > /dev/null
0.03 real 0.00 user 0.03 sys
> /usr/bin/time cat /mnt3/X11R6/bin/Xvfb > /dev/null
0.03 real 0.00 user 0.03 sys
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