Date: Mon, 26 Nov 2007 09:02:27 -0600 From: Guy Helmer <ghelmer@palisadesys.com> To: Gergely CZUCZY <phoemix@harmless.hu> Cc: freebsd-stable@freebsd.org Subject: Re: mmap max size (qemu VM memsize limit) Message-ID: <474AE003.3070206@palisadesys.com> In-Reply-To: <474ADF40.5050500@palisadesys.com> References: <20071121142404.GA7511@harmless.hu> <474ADF40.5050500@palisadesys.com>
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Guy Helmer wrote: > Gergely CZUCZY wrote: >> Hello, >> >> I'm trying to set up a qemu with 4G memory to the host system >> on a 7-BETA2, and I've hit some kind of limit in freebsd. >> >> When i give more then ~2000MB of memory to qemu, it returns >> an after trying to mmap() it, saying "Could not map physical memory". >> >> At the end of mmap(2) there's a note saying: >> " The len argument is limited to the maximum file size or >> available user- >> land address space. Files may not be able to be made more than >> 1TB large >> on 32 bit systems due to file systems restrictions and bugs, but >> address >> space is far more restrictive. Larger files may be possible on >> 64 bit >> systems." >> >> I guess I've found this limit. I've tried to check a few sysctls but >> I wasn't >> able to find the one effecting this limit. >> >> Could someone point me into the right direction in increasing the >> maximum >> mmap-able size? >> >> > If you are using the 32-bit i386 system, then you could be limited by > a couple of things, the kern.maxdsiz loader tunable or the datasize > limit are likely. On i386, I believe 1073741824 (1G) is the default > maxdsiz. With 4GB of RAM, I think you ought to be able to double > kern.maxdsiz in /boot/loader.conf. > Sorry to respond to my own posting: I just realized that the length value for mmap(), a size_t value, will become negative on i386 for values 2GB and over. That might be the source of your trouble. Guy -- Guy Helmer, Ph.D. Chief System Architect Palisade Systems, Inc.
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