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

[Stefan Karlsson]

Thanks, Per.

StefanK

On 2016-04-18 11:28, Per Liden wrote:
> Hi Stefan,
>
> On 2016-04-15 16:13, 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
>
> Looks good.
>
> cheers,
> Per
>
>>
>> 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