Request for review (XS): 8006431: os::Bsd::initialize_system_info() sets _physical_memory too large

[Bengt Rutisson]

Hi all,

Could I have a couple of reviews for this small fix?

http://cr.openjdk.java.net/~brutisso/8006431/webrev.00/

On OSX we used HW_USERMEM value from sysctl() to get the available 
physical memory on the machine. This is a 32 bit value but we store it 
in a 64 bit variable. This means that we get kind of random and normally 
very large values for what we think the physical memory is.

We actually don't want a 32 bit value since we want to handle machines 
with more than 2 or 4 GB of memory. Instead of HW_USERMEM we should be 
using HW_MEMSIZE which will give us a 64 bit value.

See:
https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man3/sysctl.3.html

Thanks Staffan Larsen for both detecting the problem and providing a 
solution.

This is a one-word-change. So, to save you a mouse click on the webrev 
link above, here is the diff:

--- a/src/os/bsd/vm/os_bsd.cpp
+++ b/src/os/bsd/vm/os_bsd.cpp
@@ -260,7 +260,7 @@
     * instead of hw.physmem because we need size of allocatable memory
     */
    mib[0] = CTL_HW;
-  mib[1] = HW_USERMEM;
+  mib[1] = HW_MEMSIZE;
    len = sizeof(mem_val);
    if (sysctl(mib, 2, &mem_val, &len, NULL, 0) != -1)
         _physical_memory = mem_val;

Thanks,
Bengt
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