RFR: JDK-8256155: os::Linux Populate all large_page_sizes, select smallest page size in reserve_memory_special_huge_tlbfs* [v9]

[Ivan Walulya]

On Mon, 7 Dec 2020 23:35:28 GMT, Marcus G K Williams <github.com+168222+mgkwill at openjdk.org> wrote:

>> When using LargePageSizeInBytes=1G, os::Linux::reserve_memory_special_huge_tlbfs* cannot select large pages smaller than 1G. Code heap usually uses less than 1G, so currently the code precludes code heap from using
>> Large pages in this circumstance and when os::Linux::reserve_memory_special_huge_tlbfs* is called page sizes fall back to Linux::page_size() (usually 4k).
>> 
>> This change allows the above use case by populating all large_page_sizes present in /sys/kernel/mm/hugepages in _page_sizes upon calling os::Linux::setup_large_page_size().
>> 
>> In os::Linux::reserve_memory_special_huge_tlbfs* we then select the largest large page size available in _page_sizes that is smaller than bytes being reserved.
>
> Marcus G K Williams has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix space format, use Linux:: for local func.
>   
>   Signed-off-by: Marcus G K Williams <marcus.williams at intel.com>

Changes requested by iwalulya (Committer).

src/hotspot/os/linux/os_linux.cpp line 3726:

> 3724: }
> 3725: 
> 3726: void os::Linux::register_large_page_sizes() {

Please refactor to remove duplicated code with` find_large_page_size`, probably use `register_large_page_sizes` to eliminate the need for `find_large_page_size`

src/hotspot/os/linux/os_linux.cpp line 4221:

> 4219: }
> 4220: 
> 4221: size_t os::Linux::select_large_page_size(size_t bytes) {

As mentioned by @tstuefe , this is duplicating `size_t os::page_size_for_region(size_t region_size, size_t min_pages, bool must_be_aligned) `

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PR: https://git.openjdk.java.net/jdk/pull/1153