RFR: JDK-8312182: THPs cause huge RSS due to thread start timing issue [v2]

[Thomas Stuefe]

On Thu, 20 Jul 2023 06:10:16 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review feedback
>
> src/hotspot/os/linux/globals_linux.hpp line 94:
> 
>> 92:   product(bool, PreventTHPsForThreadStacks, true, EXPERIMENTAL,         \
>> 93:           "If true, the JVM will attempt to prevent formation of "      \
>> 94:           "transparent huge pages in thread stacks.")                   \
> 
> Can we expand this to state that it can be turned off by ergonomics. Or better yet perhaps this should be off by default and potentially turned on by ergonomics?

As in, if THP=always, this will be turned on unless explicitly turned off? I would dislike that I cannot see the default value in globals.hpp (for numerical args, "0" is always an indication for "no value", but for bool, it looks like the real default value).

What do you think about "AllowTHPInThreadStacks" - default off, can be switched on manually to disable the mitigation if someone really wants THP for his thread stacks?

Alternative name "DisableTHPThreadStackMitigation" or somesuch, but I don't like the negation in the name.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14919#discussion_r1269010023