Question about the return value of g1CollectedHeap::expand()

[Thomas Schatzl]

Hi Jonathan,

   you are right afaict. The correct return value should be "return expanded_by > 0;" as you suggest.

I filed https://bugs.openjdk.java.net/browse/JDK-8275080. Feel free to pick it up! 🙂

Thanks,
  Thomas

________________________________
From: hotspot-gc-dev <hotspot-gc-dev-retn at openjdk.java.net> on behalf of Jonathan Joo <jonathanjoo at google.com>
Sent: Monday, October 11, 2021 10:33 PM
To: hotspot-gc-dev <hotspot-gc-dev at openjdk.java.net>
Subject: Question about the return value of g1CollectedHeap::expand()

Hello,

I'm not sure if this is a bug, but in the documentation it says that
expand() returns True if the heap was expanded by the requested amount:
https://github.com/openjdk/jdk17/blob/master/src/hotspot/share/gc/g1/g1CollectedHeap.hpp#L592

However, in the code, it seems to actually return True if the number of
regions to expand is > 0, which is not dependent on whether the expand()
call actually expands the heap or not.
https://github.com/openjdk/jdk17/blob/master/src/hotspot/share/gc/g1/g1CollectedHeap.cpp#L1318

I believe the return value should be something like `return
expanded_by > 0` (if
any heap expansion should return True), or even `return expanded_by ==
regions_to_expand` (if the full requested expansion needs to occur in order
to return True).

Am I misunderstanding something here? Thank you in advance!

~ Jonathan