From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Magenheimer Subject: RE: failed to start centos 5 domU with maxmem=30000 Date: Thu, 12 Aug 2010 05:17:31 -0700 (PDT) Message-ID: <042d87c1-bb13-436b-a5ba-9ec1578d53d0@default> References: <1281608645.5454.10.camel@vase.work> <20100812113731.GP2804@reaktio.net 1281613063.5454.15.camel@vase.work> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1281613063.5454.15.camel@vase.work> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: v.tolstov@selfip.ru, =?utf-8?B?UGFzaSBLw6Rya2vDpGluZW4=?= Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org > From: Vasiliy G Tolstov [mailto:v.tolstov@selfip.ru] > Sent: Thursday, August 12, 2010 5:38 AM > To: Pasi K=C3=A4rkk=C3=A4inen > Cc: xen-devel@lists.xensource.com > Subject: Re: [Xen-devel] failed to start centos 5 domU with > maxmem=3D30000 >=20 > =D0=92 =D0=A7=D1=82=D0=B2, 12/08/2010 =D0=B2 14:37 +0300, Pasi K=C3=A4rkk= =C3=A4inen =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > On Thu, Aug 12, 2010 at 02:24:05PM +0400, Vasiliy G Tolstov wrote: > > > Hello. I'm try to start centos domU pvm under sles 11 sp1 xen > kernel > > > with memory=3D512 and maxmem=3D30000. Centos doing boot and freeze. > > > If i'm try to use maxmem=3D15000 all works. > > > > > > Can You tell me what's wrong? > > > > > > > Is the centos PV domU 32bit or 64bit ? >=20 > 64 bit kernel-xen. >=20 > I found this in xen sources: >=20 > /* Simple continuous piecewiese linear function: > * max MiB -> min MiB gradient > * 0 0 > * 16 16 > * 32 24 > * 128 72 (1/2) > * 512 168 (1/4) > * 2048 360 (1/8) > * 8192 552 (1/32) > * 32768 1320 > * 131072 4392 > */ >=20 > Why this is not provided in documentation or on web site? Hi Vasily -- This function limits how far memory can be reduced when ballooning a guest (including dom0). It is only a heuristic but is intended to take into account the various overheads a guest Linux kernel requires to manage memory to avoid out-of-memory conditions. But I think you are correct... the same (or similar) function should be published as it also serves as a guideline for the ratio between memory=3D and maxmem=3D parameters when creating a guest: If the ratio of maxmem divided by memory is too high, the guest will not even boot. I am curious as to why you would specify memory=3D so much smaller than maxmem=3D. Are you trying to overcommit memory for guests that are often idle but sometimes use a very large amount of memory? Thanks, Dan