RFR: 8324580: SIGFPE on THP initialization on kernels < 4.10 [v3]

[Zdenek Zambersky]

On Wed, 31 Jan 2024 06:43:23 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Zdenek Zambersky has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fixed whitespace error
>
> src/hotspot/os/linux/os_linux.cpp line 3879:
> 
>> 3877:     _large_page_size = HugePages::thp_pagesize();
>> 3878:     if (_large_page_size == 0) {
>> 3879:         // Unknown THP page size => falback to default static hugepage size
> 
> Typo falback

Comments updated with resolution of the other thread.

> src/hotspot/os/linux/os_linux.cpp line 3885:
> 
>> 3883:             return;
>> 3884:         }
>> 3885:         _large_page_size = MIN2(HugePages::default_static_hugepage_size(), 16 * M);
> 
> The more I think about this, the more I doubt my own advice. What I wrote before is still true, but it may confuse users to see a page size of 16MB pop up in log files and somesuch, e.g. on intel systems.
> 
> Could you please modify this code like this:
> 
> 
> if (_large_page_size == 0) {
>   // Older kernels won't publish the THP page size. Fall back to default static huge page size,
>   // since that is likely to be the THP page size as well. Don't do it if the page size is considered
>   // too large to avoid large alignment waste.
>   log_info(pagesize) ("Cannot determine THP page size (kernel < 4.0 ?)");
>   if (HugePages::supports_static_hugepages() && 
>       HugePages::default_static_hugepage_size() <= 16 * M) {
>     _large_page_size = HugePages::default_static_hugepage_size();
>   } else {
>     warn_no_large_pages_configured();
>     UseLargePages = UseTransparentHugePages = false;
>     return;
>   }
> }
> 
> 
> and then mirror this logic in the test please.

I have updated this code and test. (just with inverted if, and fixed kernel version to 4.10)

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PR Review Comment: https://git.openjdk.org/jdk/pull/17545#discussion_r1473143031
PR Review Comment: https://git.openjdk.org/jdk/pull/17545#discussion_r1473139671