RFR: 8066875: VirtualSpace does not use large pages

[Albert Noll]

Hi Erik,

thanks a lot for taking care of this. I have one minor comment (not a 
reviewer):

1418 size_t os::largest_page_size_less_than(size_t sz) {
1419   if (UseLargePages) {
1420     // The page sizes are sorted descendingly.
1421     for (size_t i = 0; _page_sizes[i] != 0; ++i) {
1422       if (_page_sizes[i] <= sz) {
1423         return _page_sizes[i];
1424       }
1425     }
1426   }
1427   return vm_page_size();
1428 }

The function name suggests that the function returns a page size that is 
*less* than the value in the argument (sz).
However, in line 1422 you check for '<=' . I think you should either fix 
the name of the function or the check in line 1422.

Best,
Albert


On 12/10/2014 10:39 AM, Tobias Hartmann wrote:
> Hi Erik,
>
> looks good (not a reviewer).
>
> Thanks,
> Tobias
>
> On 09.12.2014 20:35, Erik Helin wrote:
>> Hi all,
>>
>> the fix for JDK-8049864 [0] made os::page_size_for_region slightly more strict
>> since the function now demands that the given region_size is size aligned with
>> respect to the chosen page_size. The reason for doing this was that
>> os::page_size_for_region was used in two ways:
>> 1. Give me a suitable page size for this amount of memory
>> 2. Give me the largest page size for this amount of memory
>> The fix for JDK-8049864 fixed os::page_size_for_region for the "suitable page
>> size" scenario, but is too strict for the "largest page size" scenario. This
>> caused a regression in VirtualSpace::initialize, which only needs the largest
>> possible page size, since VirtualSpace::initialize_with_granularity takes care
>> of any alignment issues.
>>
>> This patch adds the function os::largest_page_size_less_than and updates
>> VirtualSpace::initialize to use this new function instead of
>> os::page_size_for_region.
>>
>> Webrev:
>> http://cr.openjdk.java.net/~ehelin/8066875/webrev.00/
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8066875
>>
>> Testing:
>> - JPRT
>> - Verified that the code cache now uses large pages even if
>>    ReservedCodeCacheSize is 241 MB (see bug for more details).
>> - Added new internal vm tests (also run on SPARC machine with large
>>    pages)
>>
>> Thanks,
>> Erik
>>
>> [0]: http://hg.openjdk.java.net/jdk9/hs-gc/hotspot/rev/b326a3e8dcab