RFR: JDK-8257588: Make os::_page_sizes a set [v2]

[Thomas Stuefe]

On Thu, 3 Dec 2020 09:49:14 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix 32bit issues
>
> src/hotspot/share/runtime/os.cpp line 1904:
> 
>> 1902: size_t os::PagesizeSet::smallest() const {
>> 1903:   assert(min_page_size() > 0, "Sanity");
>> 1904:   return next_larger(min_page_size() / 2);
> 
> Why not just return `min_page_size()` here?
> 
> An assert may be added to check that they are the same though.

Not sure what you mean.

PagesizeSet::smallest() returns the smallest page in the page size set, which may be any size, or 0 if empty. 

os::_page_sizes should always contain os::vm_page_size(), but that too is not the same as os::min_page_size(). os::min_page_size() is just a constant, equal or smaller than the smallest page size across all platforms.

The naming is confusing, and probably it could be just a static const instead of a function. But I don't want to touch that with this change. But there are probably a number of misuses of os::min_page_size() where the author actually meant os::vm_page_size().

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PR: https://git.openjdk.java.net/jdk/pull/1522