From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Xen 4.0.1 "xc_map_foreign_batch: mmap failed: Cannot allocate memory" Date: Thu, 16 Dec 2010 20:54:24 +0000 Message-ID: References: <4D0A17C6020000910006886E@novprvoes0310.provo.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4D0A17C6020000910006886E@novprvoes0310.provo.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Charles Arnold , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 16/12/2010 20:44, "Charles Arnold" wrote: >>> On 12/16/2010 at 01:33 PM, in message , Keir > Fraser wrote: >> On 16/12/2010 19:23, "Charles Arnold" wrote: >> >>> The bug is that qemu-dm seems to make the assumption that it can mmap from >>> dom0 all the memory with which the guest has been defined instead of the >>> memory >>> that is actually available on the host. >> >> 32-bit dom0? Hm, I thought the qemu mapcache was supposed to limit the total >> amount of guest memory mapped at one time, for a 32-bit qemu. For 64-bit >> qemu I wouldn't expect to find a limit as low as 3.25G. > > Sorry, I should have specified that it is a 64 bit dom0 / hypervisor. Okay, well I'm not sure what limit qemu-dm is hitting then. Mapping 3.25G of guest memory will only require a few megabytes of pagetables for the qemu process in dom0. Perhaps there is a ulimit or something set on the qemu process? If we can work out and detect this limit, perhaps 64-bit qemu-dm could have a mapping cache similar to 32-bit qemu-dm, limited to some fraction of the detected mapping limit. And/or, on mapping failure, we could reclaim resources by simply zapping the existing cached mappings. Seems there's a few options. I don't really maintain qemu-dm myself -- you might get some help from Ian Jackson, Stefano, or Anthony Perard if you need more advice. -- Keir > - Charles > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel