RFR: 8067785: Using AlwaysPreTouch does not always touch all pages

[Stefan Karlsson]

Thanks, Derek!

StefanK

On 2016-04-18 21:40, Derek White wrote:
> Hi Stefan,
>
> On 4/15/16 10:13 AM, Stefan Karlsson wrote:
>> Hi all,
>>
>> Please review this patch that ensures that VirtualSpace::expand_by 
>> pre-touches all committed memory.
>>
>> http://cr.openjdk.java.net/~stefank/8067785/webrev.01
>> https://bugs.openjdk.java.net/browse/JDK-8067785
>>
>> 1) Previously, we pre-touched the memory between the old and new 
>> _high pointers. Since the _high variable isn't page aligned, the 
>> pre-touch code didn't touch all committed pages. I've moved the 
>> pre-touch code to be done for every os::commit_memory call in 
>> VirtuaSpace::expand_by.
>>
>> 2) expand_by has segregated the VirtualSpace into three segements. 
>> [small pages | large pages | small pages] so that we can have 
>> VirtualSpaces that are not large page size aligned. Previously, only 
>> the middle section called commit_memory with an alignment hint, and 
>> the small pages sections called commit_memory without a small pages 
>> hint. On all platforms, except Solaris, this boils down to the same 
>> code. On Solaris we have this additional code executed:
>>     size_t page_size = page_size_for_alignment(alignment_hint);
>>     if (page_size > (size_t) vm_page_size()) {
>>       (void)Solaris::setup_large_pages(addr, bytes, page_size);
>>     }
>>
>> But since the alignment_hint is set to vm_page_size we won't try to 
>> setup_large_pages here either.
>>
>> 3) The patch also contains a few style changes to make the 
>> VirtualSpace::expand_by easier to read (at least for me)
>>
>> Tested with JPRT and -XX:+ExecuteInternalVMTests with AlwaysPreTouch 
>> temporarily forced to true.
>>
>> Thanks,
>> StefanK
> Looks Good(tm)!
>
>  - Derek