From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: failed to start centos 5 domU with maxmem=30000 Date: Thu, 12 Aug 2010 11:34:10 -0700 Message-ID: <4C643EA2.1020300@goop.org> References: <1281608645.5454.10.camel@vase.work> <20100812113731.GP2804@reaktio.net 1281613063.5454.15.camel@vase.work> <042d87c1-bb13-436b-a5ba-9ec1578d53d0@default> <1281615845.5454.20.camel@vase.work> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1281615845.5454.20.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 Cc: Dan Magenheimer , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 08/12/2010 05:24 AM, Vasiliy G Tolstov wrote: > =D0=92 =D0=A7=D1=82=D0=B2, 12/08/2010 =D0=B2 05:17 -0700, Dan Magenheim= er =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>> 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 >>> >>> =D0=92 =D0=A7=D1=82=D0=B2, 12/08/2010 =D0=B2 14:37 +0300, Pasi K=C3=A4= rkk=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 ? >>> 64 bit kernel-xen. >>> >>> I found this in xen sources: >>> >>> /* 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 >>> */ >>> >>> 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. >> > Is that possible to use memory=3D32 and maxmem=3D60000 ? A factor of ~2000 between smallest and largest size won't work. The=20 problem is that lots of kernel structures are scaled with the amount of=20 boot-time memory, and they'll simply be overloaded when you add more=20 memory. For example, the page structure array for 60GB needs ~15.3=20 million entries, which at 64 bytes per entry will take ~980MB... >> 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? > We want to provide ability to use small as possible memory if the guest > is idle. And much as possible when the guest under heavy load. This is exactly the use-case for the hotplug memory stuff Daniel is=20 working on - which I guess is why you've been testing it. J