mmap()

[Robert Watson]

On Wed, 23 Nov 2005, Michael Conlen wrote:

> Sorry if this is the wrong place for this, but I haven't been getting 
> answers elsewhere.
>
> I'm trying to tune the system to allow very large mmap()'s in a single 
> process space, something on the order of 1.5 GB so I can pass very large 
> values for -Xms and -Xmx to java. I know I had been able to do this on 
> FreeBSD in the past but recent versions of either Java or FreeBSD aren't 
> playing nicely.  currently..

BTW, you may find it useful to use procfs to inspect the address space 
layout of your process.  You can d:

   mkdir /proc
   mount -t procfs proc /proc
   cd /proc/pid
   dd if=map of=/dev/stdout bs=20k

This can help you look for fragmentation of process address space, among 
other things.

Robert N M Watson

>
> I'm running
>
> FreeBSD host 6.0-RELEASE FreeBSD 6.0-RELEASE #0: Tue Nov 22 00:22:53 EST 2005 
> root at host:/usr/obj/usr/src/sys/WWW  i386
>
> I've also tried the following under 5.4-p1...
>
> I try
>
>        rc = mmap(0, (891*1024*1024 + 0), 0, MAP_ANON | MAP_PRIVATE, -1, 0);
>
> and it works but If I try
>
>        rc = mmap(0, (892*1024*1024 + 0), 0, MAP_ANON | MAP_PRIVATE, -1, 0);
>
> it fails returning ENOMEM.
>
> limit returns
>
> cputime      unlimited
> filesize     unlimited
> datasize     2096128 kbytes
> stacksize    1048576 kbytes
> coredumpsize unlimited
> memoryuse    unlimited
> vmemoryuse   unlimited
> descriptors  11095
> memorylocked unlimited
> maxproc      5547
> sbsize       unlimited
>
> If the program isn't doing anything else but that is there any reason I'm 
> getting limited in the amount of memory I can mmap() at about 892 MB? Ideally 
> I'd like to be able to mmap most of the 2 GB available to user procs.
>
> Oh, yes, there's plenty of free memory and swap.
>
> Thanks
>
>
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