From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [Pkg-xen-devel] Strange behavior when doing xm mem-set Domain-0 (was: Abnormal memory usage of dom0 under Squeeze leading to crash) Date: Wed, 23 Feb 2011 08:17:02 +0000 Message-ID: <1298449022.3618.617.camel@localhost.localdomain> References: <4D4A3F0C.6040607@debian.org> <20110203083413.GA19326@wavehammer.waldi.eu.org> <4D4A753E.7010106@goirand.fr> <20110203102935.GA28521@wavehammer.waldi.eu.org> <4D64B6BB.90708@goirand.fr> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0913146496==" Return-path: In-Reply-To: <4D64B6BB.90708@goirand.fr> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Thomas Goirand Cc: pkg-xen-devel@lists.alioth.debian.org, "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org --===============0913146496== Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-xbjK9wEhP1OlBS01ijT5" --=-xbjK9wEhP1OlBS01ijT5 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable On Wed, 2011-02-23 at 15:26 +0800, Thomas Goirand wrote: > On 02/03/2011 06:29 PM, Bastian Blank wrote: > > On Thu, Feb 03, 2011 at 05:28:30PM +0800, Thomas Goirand wrote: > >> On 02/03/2011 04:34 PM, Bastian Blank wrote: > >>> Please provide all informations. xm dmesg, the kernel log, xm info. > >> How, if the server reboots when I do it? > >=20 > > Well, then remove the call and gather the information before breaking > > the system. For anything else, use a serial console. >=20 > With the same server, when I put: > GRUB_CMDLINE_XEN_DEFAULT=3D"dom0_mem=3D512M" > in my /etc/default/grub, the dom0 is fine, running on 501 MB of RAM. If > I don't put this option, then shrink from something like 8 GB (the > server has 12 GB total) to bellow 800, it crashes, with no memory to > release. That's strange, because with 512 MB to the dom0, only 180M is > used, while when I give above 1GB, there's about 800MB of "used RAM", > and it can't be freed. >=20 > Any idea why it's ok to boot with 512MB on the dom0, but not ok to > mem-set Domain-0 to it? To me, it seems more a Linux issue than a Xen one= ... Linux (indeed most OSes) size certain data structures at start of day based on the amount of RAM (potentially) present. The size of these data structures does not change when ballooning occurs and since they must live in kernel memory they create a lower bound on how small you can balloon a given guest. The main one I am thinking of is the frame table (which contains an entry for every memory page in the system). On the face of it going from 8G -> 512M doesn't seem to be all that unreasonable though and I don't think the frame table would account for the full 800M overhead you are seeing. Please post a kernel and hypervisor dmesg from a boot with the larger amount of dom0 mem. The content of /proc/meminfo might be useful too as would /proc/{buddy,slab}info if your system has them. Ian. --=20 Ian Campbell Memory fault -- brain fried --=-xbjK9wEhP1OlBS01ijT5 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEABECAAYFAk1kwn4ACgkQM0+0qS9rzVnorgCgqaSf2hr6qhP3kyP+37dzbqMW eRIAoJz0mKmKjpojeZ9RGjavCumxWb+X =luCu -----END PGP SIGNATURE----- --=-xbjK9wEhP1OlBS01ijT5-- --===============0913146496== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel --===============0913146496==--