From owner-svn-src-head@freebsd.org Thu Jun 8 23:10:15 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 20EC1D861C0; Thu, 8 Jun 2017 23:10:15 +0000 (UTC) (envelope-from alc@rice.edu) Received: from pp2.rice.edu (proofpoint2.mail.rice.edu [128.42.201.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id B96E575864; Thu, 8 Jun 2017 23:10:14 +0000 (UTC) (envelope-from alc@rice.edu) Received: from pps.filterd (pp2.rice.edu [127.0.0.1]) by pp2.rice.edu (8.16.0.17/8.16.0.17) with SMTP id v58BRv4q002645; Thu, 8 Jun 2017 18:10:05 -0500 Received: from mh3.mail.rice.edu (mh3.mail.rice.edu [128.42.199.10]) by pp2.rice.edu with ESMTP id 2ay23wrf52-1; Thu, 08 Jun 2017 18:10:05 -0500 X-Virus-Scanned: by amavis-2.7.0 at mh3.mail.rice.edu, auth channel Received: from [10.87.79.168] (unknown [10.87.79.168]) (using TLSv1 with cipher RC4-MD5 (128/128 bits)) (No client certificate requested) (Authenticated sender: alc) by mh3.mail.rice.edu (Postfix) with ESMTPSA id 73CC640498; Thu, 8 Jun 2017 18:10:05 -0500 (CDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: svn commit: r319702 - head/sys/vm From: Alan Cox In-Reply-To: <1987063.fEClCI1ZXD@ralph.baldwin.cx> Date: Thu, 8 Jun 2017 18:10:05 -0500 Cc: Bryan Drewery , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <201706081618.v58GIfZi066106@repo.freebsd.org> <6910627.IXO0pzjk4q@ralph.baldwin.cx> <207FB492-94EE-47FD-BFB8-18F76C5858A5@rice.edu> <1987063.fEClCI1ZXD@ralph.baldwin.cx> To: John Baldwin X-Mailer: Apple Mail (2.3124) X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1611190142 X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 08 Jun 2017 23:10:15 -0000 > On Jun 8, 2017, at 5:28 PM, John Baldwin wrote: >=20 > On Thursday, June 08, 2017 05:07:40 PM Alan Cox wrote: >>=20 >>> On Jun 8, 2017, at 2:37 PM, John Baldwin wrote: >>>=20 >>> On Thursday, June 08, 2017 12:55:45 PM Bryan Drewery wrote: >>>> On 6/8/17 12:18 PM, John Baldwin wrote: >>>>> Author: jhb >>>>> Date: Thu Jun 8 16:18:41 2017 >>>>> New Revision: 319702 >>>>> URL: https://svnweb.freebsd.org/changeset/base/319702 >>>>>=20 >>>>> Log: >>>>> Fix an off-by-one error in the VM page array on some systems. >>>>>=20 >>>>> r31386 changed how the size of the VM page array was calculated to = be >>>>> less wasteful.=20 >>>>=20 >>>> r313186 >>>=20 >>> Oops. FWIW, this commit fixes a reliable panic booting mips and = mips64 >>> kernels under qemu. Adrian also reported the same panic on real = mips >>> hardware. >>>=20 >>=20 >> Any architecture on which we don=E2=80=99t have superpage = reservations enabled could experience the panic at boot time. Amd64, = arm, arm64, i386, and sparc64 would never panic because of the memory = allocated for the reservation array.=20 >=20 > Even then it seems to not be guaranteed. The original change has > been in CheriBSD for a while, and we have not seen any panics on boot = under > qemu as I saw with plain FreeBSD probably due to slightly different = early > memory allocations. >=20 That makes sense. Only a small subset of all possible memory sizes = would trigger the panic, and that subset amounted to only 2.5% of all = possible memory sizes.