From owner-freebsd-stable@FreeBSD.ORG Thu Dec 4 23:20:22 2008 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id DA5611065676 for ; Thu, 4 Dec 2008 23:20:22 +0000 (UTC) (envelope-from oberman@es.net) Received: from postal1.es.net (postal4.es.net [198.124.252.66]) by mx1.freebsd.org (Postfix) with ESMTP id 862878FC1D for ; Thu, 4 Dec 2008 23:20:22 +0000 (UTC) (envelope-from oberman@es.net) Received: from postal1.es.net (postal3.es.net [198.128.3.207]) by postal4.es.net (Postal Node 4) with ESMTP (SSL) id KJY84121; Thu, 04 Dec 2008 15:20:21 -0800 Received: from ptavv.es.net (ptavv.es.net [198.128.4.29]) by postal3.es.net (Postal Node 3) with ESMTP (SSL) id KJY72420; Thu, 04 Dec 2008 15:20:20 -0800 Received: from ptavv.es.net (localhost [127.0.0.1]) by ptavv.es.net (Tachyon Server) with ESMTP id 7289A45019; Thu, 4 Dec 2008 15:20:20 -0800 (PST) To: josh.carroll@gmail.com In-Reply-To: Your message of "Thu, 04 Dec 2008 17:11:46 EST." <8cb6106e0812041411t13ca9ffcjc4cc66a33ef43133@mail.gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1228432820_12904P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Thu, 04 Dec 2008 15:20:20 -0800 From: "Kevin Oberman" Message-Id: <20081204232020.7289A45019@ptavv.es.net> X-Sender-IP: 198.128.3.207 X-Sender-Domain: es.net X-Recipent: ; ; ; ; X-Sender: X-To_Name: X-To_Domain: gmail.com X-To: josh.carroll@gmail.com X-To_Email: josh.carroll@gmail.com X-To_Alias: josh.carroll Cc: Alexandr Pakhomov , Mike Tancsa , Steve Polyack Subject: Re: repeatable crash on RELENG7 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 04 Dec 2008 23:20:22 -0000 --==_Exmh_1228432820_12904P Content-Type: text/plain; charset=us-ascii Content-Disposition: inline > Date: Thu, 4 Dec 2008 17:11:46 -0500 > From: "Josh Carroll" > > > It seems that the term "swap-backed" is misleading for some people. It does > > NOT mean your md(4) device will be constantly swapping to disk (and the man > > page does an alright job of relaying this). It simply means that generally > > available memory will be used, and so will swap iff available memory happens > > to drop low enough. > > > > The bottom line in my experience with md(4) devices greater than ~100MB is > > that "swap-backed" is always reliable, while malloc'd md(4) devices will > > cause unpredictable kernel panics. > > Using -t swap instead of -t malloc will prevent a panic, but creating > an md greater than the size of the VM available and filling it will > cause resource exhaustion and OOM will kick in and start killing > processes, right? So while it won't panic the box, I still wouldn't > consider it safe to use unless the size of the md is chosen carefully. > Someone please correct me if I'm wrong, but I think that'd be the > behavior if an md with -t swap is used, right? Yes, but the VM available is just a bit larger than the amount of KVM. you still need at least a bit of sanity when you create (and fill) an MD device. For performance reasons, I suggest keeping the size of an MD so that it will fit in RAM. Paging in and out is rather painfully slow. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634 Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751 --==_Exmh_1228432820_12904P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) Comment: Exmh version 2.5 06/03/2002 iD8DBQFJOGW0kn3rs5h7N1ERAh9jAJoDr0hX/7rTzLodd6wF8gm0MsfdLACfebHl FSfNU/zkkOoIxPN91Owe/V0= =hyxw -----END PGP SIGNATURE----- --==_Exmh_1228432820_12904P--