Staffan, Bengt, Mikael,
Thanks for the reviews!
I have made the changes you have suggested and a new webrev is available at:
http://cr.openjdk.java.net/~jwilhelm/8028391/webrev.5/
I agree with your assessment that it would be good to implement a generic way to
verify manageable flags. I think it is a separate change though so I will not
attack that problem in this change.
As Mikael wrote in his review we have talked offline about the changes and how
to make them more correct and readable. Thanks Mikael for the input!
More comments inline.
Bengt Rutisson skrev 22/1/14 11:21 AM:
Hi Jesper,
The calculation in PSAdaptiveSizePolicy::calculated_old_free_size_in_bytes()
looks wrong to me. I would have expected this:
86 // free = (live*ratio) / (1-ratio)
87 size_t max_free = (size_t)((heap->old_gen()->used_in_bytes() *
mhfr_as_percent) / (1.0 - mhfr_as_percent));
to be something like this:
size_t max_free = heap->old_gen()->capacity_in_bytes() * mhfr_as_percent;
The suggested formula above will calculate how much free memory there can be
based on the current old gen size. What I want to achieve in the code is to
calculate how much free memory there can be based on the amount of live data in
the old generation. I have talked to Bengt offline and he agrees that the code
is doing what I want it to. I have rewritten the code and added more comments to
explain the formula.
(A minor naming thing is that mhfr_as_percent is actually not a percent but a
ratio or fraction. Just like you write in the comment.)
Right. Fixed.
We also don't seem to take MinHeapFreeRatio into account. Should we do that?
We should. Good catch! I have added support for MinHeapFreeRatio both here and
in psScavenge.cpp.
I think it should be possible to write a internal VM test or a whitebox test for
the calculated_old_free_size_in_bytes() to verify that it produces the correct
results.
I've added an internal test to verify the new code.
Speaking of testing. There is already a test called
test/gc/arguments/TestHeapFreeRatio.java. That test seems to pass with the
ParallelGC already before your changes. I think that means that the test is not
strict enough. Could you update that test or add a new test to make sure that
your changes are tested?
TestHeapFreeRatio only verifies that the VM gives correct error messages for the
-Xminf and -Xmaxf flags. Since HotSpot usually don't complain about flags that
don't affect the chosen GC, there is no error given about ParallelGC not
implementing the heap ratio flags. The code I change is not tested by this test.
Dmitry Fazunenko has developed a test for the new feature which I have used
while developing. This test will be pushed once the feature is in place.
I also agree with Staffan that the methods is_within() and is_min() make it
harder to read the code.
Yes, me to...
I removed them.
Thanks,
/Jesper
Thanks,
Bengt
On 2014-01-22 09:40, Staffan Larsen wrote:
Jesper,
This looks ok from a serviceability perspective. Long term we should probably
have a more pluggable way to verify values of manageable flags so we can avoid
some of the duplication.
I have a slight problem with is_within() and is_min() in that it is not
obvious from the call site if the min and max values are inclusive or not - it
was very obvious before.
/Staffan
On 21 jan 2014, at 22:49, Jesper Wilhelmsson <jesper.wilhelms...@oracle.com>
wrote:
Hi,
Could I have a few reviews of this change?
Summary:
To allow applications a more fine grained control over the GC over time,
we'll make the flags MinHeapFreeRatio and MaxHeapFreeRatio manageable.
The initial request that lead up to this change involved ParallelGC which is
notoriously unwilling to shrink the heap. Since ParallelGC didn't support the
heap free ratio flags, this change also includes implementing support for
these flags in ParallelGC.
Changes have also been made to the argument parsing, attach listener and the
management API to verify the flag values when set through the different
interfaces.
Webrev: http://cr.openjdk.java.net/~jwilhelm/8028391/webrev.4/
Bug: https://bugs.openjdk.java.net/browse/JDK-8028391
The plan is to push this to 9 and then backport to 8 and 7.
Thanks!
/Jesper
