RFR: 8256155: Allow multiple large page sizes to be used on Linux [v34]

[Marcus G K Williams]

On Wed, 12 May 2021 16:16:33 GMT, Marcus G K Williams <mgkwill at openjdk.org> wrote:

>> Change the meaning of LargePageSizeInBytes to be the maximum large page size the JVM may use (not the only one). A default value of zero will mean to allow the JVM use large page sizes up to the system's default large page size.
>
> Marcus G K Williams has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Check large pages =< _large_page_size
>   
>   Signed-off-by: Marcus G K Williams <marcus.williams at intel.com>

src/hotspot/os/linux/os_linux.cpp line 3789:

> 3787:       break;
> 3788:     }
> 3789:   }

> While doing some manual testing I found a problem when setting `LargePageSizeInBytes=1g`, but without having any 1g pages configured. In that case, we will turn off `UseLargePages` even if there are 2m pages configured.
> 
> Not sure if we should address this as part of this change or as a follow up, but I think the `hugetlbfs_sanity_check(...)` should check that at least one of the supported large pages are configured, not just the one set as the maximum large page size.

@kstefanj How about this as a solution?

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