RFR: 8244752: Enable Linux support for multiple huge page sizes -XX:LargePageSizeInBytes

[stefan.johansson at oracle.com]

Hi Ivan,

On 2020-05-14 15:42, Ivan Walulya wrote:
> Hi Thomas,
> 
> Thanks for the comments
>>
>> 2952 // If MAP_HUGETLB is set, and the system supports multiple huge page sizes,
>> 2953 // flag bits [26:31] can be used to encode the log2 of the desired huge page size.
>> 2954 // Otherwise the system's default huge page size will be used.
>> 2955 // See mmap(2) man page for more info (since Linux 3.8).
>> 2956 // https://lwn.net/Articles/533499/ <https://urldefense.com/v3/__https://lwn.net/Articles/533499/__;!!GqivPVa7Brio!LmDQYi0jNiIRDJQ6zF29nJULj1sCUcKePWCy8dlGpPKazvDIpkndYUSSAz8-tgpCER8$>
>> 2957 #ifndef MAP_HUGE_SHIFT
>> 2958   #define MAP_HUGE_SHIFT 26
>> 2959 #endif
>>
>> I may be slow but I needed a while to understand this comment; as a standalone comment it is confusing. What flags? Could you clarify the comment a bit, especially making clear that "flags" means mmap flags to be used in conjunction with MAP_HUGE_TLB?
>>
>> ---
>>
>> bool os::Linux::is_valid_large_page_size(size_t large_page_size)
>>
> 
>> Note that os::Linux::is_valid_large_page_size() sounds rather inconspicuous; as a caller, without looking at the implementation, I would not have assumed it does file IO.
> 
> Refactored to address the above comments
> 
> New webrev: http://cr.openjdk.java.net/~iwalulya/8244752/02/
Looks good,
Stefan

> 
> //Ivan
>