From owner-freebsd-hackers Thu Apr 12 14:26:20 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from earth.backplane.com (earth-nat-cw.backplane.com [208.161.114.67]) by hub.freebsd.org (Postfix) with ESMTP id 0FDEC37B422 for ; Thu, 12 Apr 2001 14:26:18 -0700 (PDT) (envelope-from dillon@earth.backplane.com) Received: (from dillon@localhost) by earth.backplane.com (8.11.2/8.11.2) id f3CLOaq25845; Thu, 12 Apr 2001 14:24:36 -0700 (PDT) (envelope-from dillon) Date: Thu, 12 Apr 2001 14:24:36 -0700 (PDT) From: Matt Dillon Message-Id: <200104122124.f3CLOaq25845@earth.backplane.com> To: Poul-Henning Kamp Cc: Rik van Riel , David Xu , freebsd-hackers@FreeBSD.ORG Subject: Re: vm balance References: <59487.987108936@critter> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG :>:> scaleability. :>: :>:Uhm, that is actually not true. :>: :>:We keep namecache entries around as long as we can use them, and that :>:generally means that recreating them is a rather expensive operation, :>:involving creation of vnode and very likely a vm object again. :> :> The vnode cache is a different cache. positive namei hits will :> reference a vnode, but namei elements can be flushed at any :> time without flushing the underlying vnode. : :Right, but doing so means that to refind that vnode from the name :is (comparatively) very expensive. : :-- :Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 :phk@FreeBSD.ORG | TCP/IP since RFC 956 The only thing that is truely expensive is having to physically scan a large directory in order to instantiate a new namei record. Everything else is inexpensive by comparison (by two orders of magnitude!), even constructing new vnodes. Without vmiodirenable turned on, any directory exceeding vfs.maxmallocbufspace becomes extremely expensive to work with O(N * diskIO). With vmiodirenable turned on huge directories are O(N), but have a better chance of being in the VM page cache so cost proportionally less even though they don't do any better on a relative scale. -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message