RFR: 8262291: Refactor reserve_memory_special_huge_tlbfs

[Ivan Walulya]

On Tue, 23 Mar 2021 20:20:15 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

>> src/hotspot/os/linux/os_linux.cpp line 3929:
>> 
>>> 3927: }
>>> 3928: 
>>> 3929: char* os::Linux::reserve_and_commit_special(size_t bytes,
>> 
>> method name `reserve_and_commit_`  implicitly suggests that other methods with just `reserve_memory_` do not commit (to me).
>
> That is a good point, I've struggled a bit with this function name. Since we actually do the reservation using the call to `anon_mmap_aligned()` maybe this one should just be called: `commit_memory_special()`

yes, seems better to me

>> src/hotspot/os/linux/os_linux.cpp line 3990:
>> 
>>> 3988:   char* large_mapping = reserve_and_commit_special(large_bytes, os::large_page_size(), aligned_start, exec);
>>> 3989: 
>>> 3990:   if (bytes == large_bytes) {
>> 
>> Shouldn't we do the check `if (large_mapping == NULL) {` before this?
>
> We could, and I thought about adding a comment here. I probably should have. The reason we don't do the explicit check it is that if `large_mapping == NULL` then NULL will be returned as expected and there is no additional work to be done if `bytes == large_bytes`.

ok, now I get it. I had missed that when mmap fails, the original reservation is unmapped for this range so no need to do any additional clean up.

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PR: https://git.openjdk.java.net/jdk/pull/3073