From owner-freebsd-hackers@FreeBSD.ORG Mon Apr 21 22:22:12 2014 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 1CE8AE00 for ; Mon, 21 Apr 2014 22:22:12 +0000 (UTC) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "funkthat.com", Issuer "funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id D59031FF7 for ; Mon, 21 Apr 2014 22:22:11 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id s3LMMAfN080167 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 21 Apr 2014 15:22:10 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id s3LMMACc080166; Mon, 21 Apr 2014 15:22:10 -0700 (PDT) (envelope-from jmg) Date: Mon, 21 Apr 2014 15:22:10 -0700 From: John-Mark Gurney To: Chris Torek Subject: Re: MAXPHYS in md(4) Message-ID: <20140421222210.GW43976@funkthat.com> Mail-Followup-To: Chris Torek , freebsd-hackers@freebsd.org References: <201404212215.s3LMFstd045652@elf.torek.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201404212215.s3LMFstd045652@elf.torek.net> User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-TipJar: bitcoin:13Qmb6AeTgQecazTWph4XasEsP7nGRbAPE X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Mon, 21 Apr 2014 15:22:10 -0700 (PDT) Cc: freebsd-hackers@freebsd.org X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Apr 2014 22:22:12 -0000 Chris Torek wrote this message on Mon, Apr 21, 2014 at 16:15 -0600: > In svn commit: r264504 - head/sys/geom/uzip we have: > > Make sure not to do I/O for more than MAXPHYS bytes. Doing so can cause > problems in our providers, such as a KASSERT in md(4). ... > > That would be this one: > > KASSERT(bp->bio_length <= MAXPHYS, ("bio_length %jd", > (uintmax_t)bp->bio_length)); > if ((bp->bio_flags & BIO_UNMAPPED) == 0) { > pb = NULL; > aiov.iov_base = bp->bio_data; > } else { > pb = getpbuf(&md_vnode_pbuf_freecnt); > ... > > As it happens, the KASSERT is really only required for the > pb != NULL case, which uses one of the reserved getpbuf() buffers > that only map MAXPHYS bytes at a time. If bp->bio_flags says that > the bio is mapped, we just use the existing KVA, and VOP_READ() and > VOP_WRITE() must already break up arbitrarily large transfers. > > So, it seems like the md(4) KASSERT can be moved into the "else". > Is this a good idea? (It might not help r264504 much since it > looks like r264504 wants to handle short-read results anyway, but > it seems overly restrictive to require <= MAXPHYS for the mapped > cases.) This really should be moved up into the generic GEOM layer so geom module ever sees IO that is larger than MAXPHYS... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."