RFR(xxs): 8187230: [aix] Leave OS guard page size at default for non-java threads instead of explicitly setting it

[David Holmes]

Hi Chris,

On 8/09/2017 7:07 AM, Chris Plummer wrote:
> Hi Thomas,
> 
> Is there a reason this shouldn't also be done for linux?

It probably could given "The default guard size is the same as the 
system page size." so the end result would be the same.

But then perhaps this whole default_guard_size logic should disappear, 
if all we ever need to do is disable guards for JavaThreads? But this 
seems out of scope for what Thomas wanted to fix - unless he wants to 
extend the scope of course ;-)

Cheers,
David

> thanks,
> 
> Chris
> 
> On 9/7/17 3:02 AM, Thomas Stüfe wrote:
>> Hi all,
>>
>> may I please have a review for this small change:
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8187230
>>
>> Webrev:
>> http://cr.openjdk.java.net/~stuefe/webrevs/8187230-aix-
>> leave-os-guard-page-size-at-default-for-non-java-threads/webrev.00/webrev/ 
>>
>>
>> The change is very subtle.
>>
>> Before, we would set the OS guard page size for every thread - for java
>> threads disable them, for non-java threads we'd set them to 4K.
>>
>> Now, we still disable them for java threads but leave them at the OS
>> default size for non-java threads.
>>
>> The really important part is the disabling of OS guard pages for java
>> threads, where we have a VM guard pages in place and do not want to spend
>> more memory on OS guards. We do not really care for the exact size of the
>> OS guard pages for non-java threads, and therefore should not set it - we
>> should leave the size in place the OS deems sufficient. That also 
>> spares us
>> the complexity of handling the thread stack page size, which on AIX 
>> may be
>> different from os::vm_page_size().
>>
>> Thank you and Kind Regards, Thomas
> 
> 
>