CRR (S/M): 7092309: G1: introduce old region set

Bengt Rutisson bengt.rutisson at
Thu Oct 6 11:04:04 UTC 2011

Hi Tony,

This looks good. It will be great to have the old region set for the CR 
regarding humungous allocation and concurrent mark start that I am 
working on.

Some comments regarding MasterOldRegionSet::check_mt_safety():

The code would be easier (at least for me) to read like this:

   if (SafepointSynchronize::is_at_safepoint()) {
     guarantee(Thread::current()->is_VM_thread() ||
              (_phase == HRSPhaseEvacuation && 
FreeList_lock->owned_by_self()) ||
              (_phase == HRSPhaseCleanup && 
OldSets_lock->owned_by_self()), "Master old set MT safety protocol: 
safepoint invariants violated");
   } else {
     guarantee(Heap_lock->owned_by_self(), "Master old set MT safety 
protocol: Heap lock must be held if we are not at a safepoint");

It would also align nicely with how you structured the comment just 
above the guarantee.

Also, the only call to check_mt_safety() that I could find is in 
hrs_assert_mt_safety_ok() and there we call it from an assert. If that 
is correct, why are then the check_mt_safety() implementations using 
guarantees and not asserts?


On 2011-10-04 21:54, Tony Printezis wrote:
> Hi all,
> This change adds to G1 the facility to keep track of the allocated old 
> regions with the HeapRegionSet abstraction and moves us one step 
> closer to having all regions being tracked by the same abstraction 
> (after this, only the survivor / eden regions remain). I decided to 
> work on the old region set now as it was a relatively easy change to 
> implement and will make some follow-on CRs easier to implement. The 
> webrev is here:
> Most of the changes were straightforward (I largely followed how we 
> maintain the humongous region set). The only part which I had to 
> slightly revamp was the code that tears down / rebuilds the region 
> sets. This small refactoring, though, was worthwhile as it makes that 
> code easier to extend in the future (when we introduce the eden / 
> survivor lists).
> Tony

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