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

[Vitaly Davidovich]

Also, is it worthwhile to initialize mem_value to 0 explicitly before
passing it to the syscall? That should avoid garbage in the upper 32 bits;
I realize it's not needed now but maybe for completeness sake?

Sent from my phone
On Jan 18, 2013 8:57 AM, "Vitaly Davidovich" <vitalyd at gmail.com> wrote:

> Hi Bengt,
>
> The comment there needs to be updated because it's still talking about
> usermem.
>
> Thanks
>
> Sent from my phone
> On Jan 18, 2013 7:48 AM, "Bengt Rutisson" <bengt.rutisson at oracle.com>
> wrote:
>
>>
>>
>> Hi Mikael,
>>
>> Thanks for the review!
>>
>> On 1/18/13 8:09 AM, Mikael Vidstedt wrote:
>>
>>
>>  Looks good, assuming u_long is a 64-bit type.
>>
>>
>> Good point. It seems like u_long is a 64 bit value on OSX, but that's not
>> guaranteed since it is just "unsigned long". I changed mem_val to be
>> julong, which should always be 64 bit. (The instance variable
>> _physical_memory is also a julong.)
>>
>> So, now it is a two-word review request  :)
>>
>> diff --git a/src/os/bsd/vm/os_bsd.cpp b/src/os/bsd/vm/os_bsd.cpp
>> --- a/src/os/bsd/vm/os_bsd.cpp
>> +++ b/src/os/bsd/vm/os_bsd.cpp
>> @@ -243,7 +243,7 @@
>>    int mib[2];
>>    size_t len;
>>    int cpu_val;
>> -  u_long mem_val;
>> +  julong mem_val;
>>
>>    /* get processors count via hw.ncpus sysctl */
>>    mib[0] = CTL_HW;
>> @@ -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
>>
>>
>>
>> /Mikael
>>
>> On 17 jan 2013, at 22:36, Bengt Rutisson <bengt.rutisson at oracle.com>
>> wrote:
>>
>>
>> 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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