RFR: 8346005: Parallel: Incorrect page size calculation with UseLargePages [v6]

[Albert Mingkun Yang]

On Thu, 2 Oct 2025 09:11:51 GMT, Joel Sikström <jsikstro at openjdk.org> wrote:

>> Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
>> 
>>  - Merge branch 'master' into pgc-largepage
>>  - Merge branch 'master' into pgc-largepage
>>  - page-size
>>  - Merge branch 'master' into pgc-largepage
>>  - Merge branch 'master' into pgc-largepage
>>  - Merge branch 'master' into pgc-largepage
>>  - pgc-largepage
>
> src/hotspot/share/gc/parallel/parallelArguments.cpp line 131:
> 
>> 129:   if (page_sz == os::vm_page_size()) {
>> 130:     log_warning(gc, heap)("MinHeapSize (%zu) must be large enough for 4 * page-size; Disabling UseLargePages for heap", MinHeapSize);
>> 131:     return;
> 
> Wouldn't it make sense to do `FLAG_SET_ERGO(UseLargepages, false)` here since it is effectively disabled.

There are non-heap uses of `UseLargePages` as well. Here we concluded heap can't use large-page, but other systems still can.

> To me it looks like new_alignment will always be different from SpaceAlignment here. 

Why so? (I know the default value of SpaceAlignment is 64K*8 bytes, which is not a common large-page-size, but that info is not directly accessible in this context.)

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/26700#discussion_r2398090623
PR Review Comment: https://git.openjdk.org/jdk/pull/26700#discussion_r2398130690