Hi Doug,
The JVMTI related part looks good to me.
Thank you for fixing it!
Thanks,
Serguei
On 10/2/18 1:11 AM, Doug Simon wrote:
It would be great to get some input from the non-compilers teams on this RFR.
-Doug
On 28 Sep 2018, at 19:51, Vladimir Kozlov <vladimir.koz...@oracle.com> wrote:
To let you know, me and Tom R. did review these changes and agreed that it is
the least intrusive changes for Hotspot shared code.
Thanks,
Vladimir
On 9/25/18 8:11 AM, Daniel D. Daugherty wrote:
Adding serviceability-dev@... since this is JVM/TI...
Dan
On 9/25/18 10:48 AM, Doug Simon wrote:
A major design point of Graal is to treat allocations as non-side effecting to
give more freedom to the optimizer by reducing the number of distinct
FrameStates that need to be managed. When failing an allocation, Graal will
deoptimize to the last side effecting instruction before the allocation. This
mean the VM code for heap allocation will potentially be executed twice, once
from Graal compiled code and then again in the interpreter. While this is
perfectly fine according to the JVM specification, it can cause confusing
behavior for JVMTI based tools. They will receive 2 ResourceExhausted events
for a single allocation. Furthermore, the first ResourceExhausted event (on the
Graal allocation slow path) might denote a bytecode instruction that performs
no allocation, making it hard to debug the memory failure.
The proposed solution is to add an extra set of JVMCI VM runtime calls for
allocation. These entry points will attempt the allocation and upon failure,
skip side-effects such as posting JVMTI events or handling
-XX:OnOutOfMemoryError. The compiled code using these entry points is expected
deoptmize on null.
The path from these new entry points to where allocation can fail goes through
quite a bit of VM code. One could modify all these paths by:
* Returning null instead of throwing an exception on failure.
* Adding a `bool null_on_fail` argument to all relevant methods.
* Adding extra null checking where necessary after each call to these methods
when `null_on_fail == true`.
This represents a significant number of changes.
Instead, the proposed solution introduces a new _in_retryable_allocation
thread-local. This way, only the entry points and allocation routines that
raise an exception need to be modified. Failure is communicated back to the new
entry points by throwing a special pre-allocated OOME object (i.e.,
Universe::out_of_memory_error_retry()) which must not propagate back to Java
code. Use of this object is not strictly necessary; it is introduced to
highlight/document the special allocation mode.
The proposed solution is at http://cr.openjdk.java.net/~dnsimon/8208686.
THE JBS bug is: https://bugs.openjdk.java.net/browse/JDK-8208686
-Doug
