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Add warnings for potential ergonomics failures for JDK8/Windows #48968

Merged
merged 2 commits into from
Nov 12, 2019
Merged

Add warnings for potential ergonomics failures for JDK8/Windows #48968

merged 2 commits into from
Nov 12, 2019

Commits on Nov 11, 2019

  1. Warn when MaxDirectMemorySize may be incorrect (Windows/JDK8 only iss… 

    …ue) (elastic#48365)

Our JVM ergonomics extract max heap size from JDK PrintFlagsFinal output. 
On JDK 8, there is a system-dependent bug where memory sizes are cast to 
32-bit integers. On affected systems (namely, Windows), when 1/4 of physical
memory is more than the maximum integer value, the output of PrintFlagsFinal
will be inaccurate. In the pathological case, where the max heap size would
be a multiple of 4g, the test will fail.

The practical effect of this bug, beyond test failures, is that we may set
MaxDirectMemorySize to an incorrect value on Windows. This commit adds a
warning about this situation during startup.
    @williamrandolph
    williamrandolph committed Nov 11, 2019
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  2. Don't drop user's MaxDirectMemorySize flag on jdk8/windows (elastic#4… 

    …8657)

* Always pass user-specified MaxDirectMemorySize

We had been testing whether a user had passed a value for
MaxDirectMemorySize by parsing the output of "java -XX:PrintFlagsFinal
-version". If MaxDirectMemorySize equals zero, we set it to half of max
heap. The problem is that on Windows with JDK 8, a JDK bug incorrectly
truncates values over 4g and returns multiples of 4g as zero. In order
to always respect the user-defined settings, we need to check our input
to see if an "-XX:MaxDirectMemorySize" value has been passed.

* Always warn for Windows/jdk8 ergo issue

Even if a user has set MaxDirectMemorySize, they aren't future-proof for
this JDK bug. With this change, we issue a general warning for the
windows/JDK8 issue, and a specific warning if MaxDirectMemorySize is
unset.
    @williamrandolph
    williamrandolph committed Nov 11, 2019
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