Date: Thu, 1 May 2008 18:15:40 +0200 From: Peter Schuller <peter.schuller@infidyne.com> To: freebsd-current@freebsd.org Cc: Andrew Gallatin <gallatin@cs.duke.edu> Subject: Re: ZFS file caching question Message-ID: <200805011815.50808.peter.schuller@infidyne.com> In-Reply-To: <480F4972.20609@FreeBSD.org> References: <18447.17658.759349.720175@grasshopper.cs.duke.edu> <480F4972.20609@FreeBSD.org>
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--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--
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