Re: [rvm-research] A question about Full Heap Mark Sweep

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The MMTk MarkSweep collector uses a segregated free list as its
allocator.  Because there are a finite number of size classes in the
allocator, there is a maximum object size beyond which the space
cannot handle (8192 bytes by default) - for these objects we use a
collector based on Baker's treadmill, i.e. the large object space
Nathan mentions.

In practice (depending on the benchmark) the vast majority of objects
in the heap are allocated in the mark sweep space.  The exact
percentage would be simple to measure.

In practice, I believe the performance of the existing mark-sweep
collector is a very close approximation to a pure mark-sweep
collector, probably within the limits of experimental error.  The
SemiSpace collector probably exhibits more departure from a pure
semi-space collector, because the large object space is implemented in
order to avoid the overhead of copying large objects on each collection.

It would be a simple exercise to extend the free list allocator to add
more size classes and accommodate more of the large objects.  Indeed
for a specific benchmark you could design size classes that would
accommodate 100% of objects.


Hotspot is very much wedded to a generational collector, and I don't
believe it's possible to tweak the GC settings to bypass the nursery
(at least not in the documented settings).  You can bypass the
survivor space using -XX:InitialTenuringThreshold=0
- -XX:MaxTenuringThreshold=0, so you should be able to roughly
approximate the MMTk GenMS collector.

regards,
Robin

On 11/02/14 08:32, lipengcheng wrote:
> Thanks for your reply, Nathan.
> 
> So do you know where we can get a totally full heap mark sweep
> collector ? I have metric and want to verify its correctness, which
> heavily relies on a full heap mark sweep collector.
> 
> Thanks, -Pengcheng
> 
> On Feb 10, 2014, at 4:18 PM, Nathan Ricci <[email protected] 
> <mailto:[email protected]>> wrote:
> 
>> Pengcheng,
>> 
>> Yes, there is a full heap mark sweep collector in JikesRVM. There
>> are still some objects that end up in other spaces (like the 
>> large object space) even when using the MarkSweep collector
>> though.
>> 
>> --Nathan Ricci
>> 
>> 
>> On Mon, Feb 10, 2014 at 3:28 PM, lipengcheng
>> <[email protected] <mailto:[email protected]>> wrote:
>> 
>> Dear RVM/MMTK researchers,
>> 
>> May I ask that if JikeVM supports full heap mark sweep GC, not a 
>> generational GC ? Or does everyone know if Hotspot JVM supports a
>> full heap mark sweep GC ? Thanks,
>> 
>> Best, -Pengcheng 
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Android apps run on BlackBerry 10
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Now with support for Jelly Bean, Bluetooth, Mapview and more.
Get your Android app in front of a whole new audience.  Start now.
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