mmap max size (qemu VM memsize limit)

[Guy Helmer]

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.