From owner-freebsd-current@FreeBSD.ORG  Thu May  1 16:15:00 2008
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id EDAB61065679
	for <freebsd-current@freebsd.org>; Thu,  1 May 2008 16:15:00 +0000 (UTC)
	(envelope-from peter.schuller@infidyne.com)
Received: from smtp.infidyne.com (ds9.infidyne.com [88.80.6.206])
	by mx1.freebsd.org (Postfix) with ESMTP id A246F8FC20
	for <freebsd-current@freebsd.org>; Thu,  1 May 2008 16:15:00 +0000 (UTC)
	(envelope-from peter.schuller@infidyne.com)
Received: from c-a916e555.03-51-73746f3.cust.bredbandsbolaget.se
	(c-a916e555.03-51-73746f3.cust.bredbandsbolaget.se [85.229.22.169])
	by smtp.infidyne.com (Postfix) with ESMTPSA id 5261E8B189;
	Thu,  1 May 2008 18:14:58 +0200 (CEST)
From: Peter Schuller <peter.schuller@infidyne.com>
To: freebsd-current@freebsd.org
Date: Thu, 1 May 2008 18:15:40 +0200
User-Agent: KMail/1.9.7
References: <18447.17658.759349.720175@grasshopper.cs.duke.edu>
	<480F4972.20609@FreeBSD.org>
In-Reply-To: <480F4972.20609@FreeBSD.org>
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="nextPart1424672.qGF4LMVXX2";
	protocol="application/pgp-signature"; micalg=pgp-sha1
Content-Transfer-Encoding: 7bit
Message-Id: <200805011815.50808.peter.schuller@infidyne.com>
Cc: Andrew Gallatin <gallatin@cs.duke.edu>
Subject: Re: ZFS file caching question
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 01 May 2008 16:15:01 -0000

--nextPart1424672.qGF4LMVXX2
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

> on FreeBSD.  This is inefficient in a number of ways.  I have also seen
> things that make me suspicious that it is not caching properly even when
> you tune it to be "large enough" (if possible given memory constraints),
> but I haven't confirmed this.

=46WIW, I have had some suspiciouns here too strictly from a user-centric p=
oint=20
of view.

Most recently I found that I could not get ZFS to cache enough such=20
that "pkg_info" would not have to get down on disk (thus making all package=
=20
installation and similar dead-slow, due to the number of times /var/db/pkg =
is=20
accesses in deep dependency hierarchies).

In this case I tended up killing as much as I could  on the machine (web=20
browsers, MUA:s, whatever else), on the theory that large files being kept=
=20
open would affect the caching strategy. Even after killing most stuff and=20
after multiple pkg_info:s (to accumulate frequency), it was still only=20
caching enough for perhaps 20% of what pkg_info needs on this machine (when=
=20
invoked without arguments, listing all packages).

I don't know if this is just a result of giving too much weight to past=20
history or if there is an actual bug somewhere; but the perceived end-resul=
t=20
for me as a user was clearly significantly worse than a plain page-wise LRU=
=20
would have given.

I ended up rebooting the machine to get package upgrades to complete within=
 a=20
reasonable amount of time.

This was on my 64 bit desktop machine with:

vm.kmem_size_max=3D"1258291200"
vfs.zfs.prefetch_disable=3D"1"
vfs.zfs.arc_max=3D"838860800"

=2D-=20
/ Peter Schuller

PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller@infidyne.com>'
Key retrieval: Send an E-Mail to getpgpkey@scode.org
E-Mail: peter.schuller@infidyne.com Web: http://www.scode.org


--nextPart1424672.qGF4LMVXX2
Content-Type: application/pgp-signature; name=signature.asc 
Content-Description: This is a digitally signed message part.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.8 (FreeBSD)

iEYEABECAAYFAkgZ7LYACgkQDNor2+l1i33wKACfYBSTAJlFDnUe9aBilLEcAuf/
GmIAmwWAGKjltx/h5eihARvJNmLAgXti
=h0/j
-----END PGP SIGNATURE-----

--nextPart1424672.qGF4LMVXX2--