increase the hard limit on i386 max data size to 2GB-1.  This will allow 
memory hungry processes to potentially use more RAM if you increase data 
limits appropriately.

Index: vmparam.h
===================================================================
RCS file: /home/tedu/cvs/src/sys/arch/i386/include/vmparam.h,v
retrieving revision 1.45
diff -u -r1.45 vmparam.h
--- vmparam.h	15 Dec 2010 05:30:19 -0000	1.45
+++ vmparam.h	24 Dec 2010 21:52:07 -0000
@@ -63,7 +63,7 @@
 #define	DFLDSIZ		(64*1024*1024)		/* initial data size limit */
 #endif
 #ifndef MAXDSIZ
-#define	MAXDSIZ		(1024*1024*1024)	/* max data size */
+#define	MAXDSIZ		(2UL*1024*1024*1024-1)	/* max data size. -1 to avoid overflow */
 #endif
 #ifndef BRKSIZ
 #define	BRKSIZ		(1024*1024*1024)	/* heap gap size */

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On Fri, Dec 24, 2010 at 5:02 PM, Mark Kettenis <mark.kettenis@xs4all.nl>

Anyone who stores the limit in a signed int (or long).  Do I know of
any such software?  No.  Am I willing to risk the possibility of such
existing to squeeze out a few more bytes?  No.

I will happily set it to straight 2GB, or even higher if we don't care
about possible trouble, so long as everybody promises not to complain
if an issue is found. :)

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To phrase it another way, I was actually hoping that by avoiding the
"what about overflow?" worries, we could move forward faster.  If
that's not a worry, great, I just didn't want to get tied down.

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You mean, in the kernel?  There the limits are stored in rlim_t, which
is a 64-bit type on all our architectures.  There is one comparison in
uvm_mmap.c that had me worried for a bit:

    if (size >
        (p->p_rlimit[RLIMIT_DATA].rlim_cur - ptoa(p->p_vmspace->vm_dused))) {

but this is safe since ptoa() casts to paddr_t, which is unsigned long.

There is also 'struct orlimit' in <sys/resource.h>, which is used for
BSD4.3 compat code in compat/common/kern_resource_43.c.  But
RLIMIT_DATA isn't the only resource limit that can be set to 2GB or
beyond.  So I'm happy to ignore that issue.

For userland, I have very little sympathy.  If stuff doesn't run with
the limits cranked up all the way to 2GB, fix it, or crank the limit

I don't think this is a worry.  Wouldn't mind if somebody else takes a
look at this as well.

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