RFR: 8212921: Relax code cache oop verification in ZGC
per.liden at oracle.com
Wed Oct 31 15:47:44 UTC 2018
Ok, thanks for reviewing, Erik.
On 10/31/2018 03:19 PM, Erik Österlund wrote:
> Hi Per,
> I prefer your approach - it allows more verification which is good.
> Looks good. I'll reassign this to you.
> On 2018-10-31 15:10, Per Liden wrote:
>> On 10/25/2018 03:18 PM, Erik Österlund wrote:
>>> With concurrent class unloading, the normal state of affairs for ZGC
>>> is that nmethods have messed up oops in all GC safepoints, and fix
>>> them up during concurrent phases. Therefore, Universe::verify needs
>>> to relax the assumption that oops are okay for ZGC.
>>> Note that during Universe::verify, the oops in the nmethods were
>>> redundantly verified. Once by walking the oops in the code cache, and
>>> once when calling nmethod::verify(), which did the same verification
>>> again. I removed the latter.
>> I discussed this with Erik off-line. Instead of adjusting the
>> verification code to do what ZGC needs, we could instead move ZGC's
>> verification to after resurrection is unblocked. At this time, all
>> oops we find will be good and no special nmethod verification will be
>> Here's a webrev to adjust to that model:
>> I also noticed that we could remove some boilerplate code by fusing
>> ZVerifyRootOopClosure and ZVerifyHeapOopClosure into a single
>> ZVerifyOopClosure, which I did.
>> I still agree that the current double verification of nmethod oops
>> seems completely unnecessary, but it's harmless so that can be handled
>> by a separate RFE.
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