Ok, thanks Clément for the explanation. what do you mean with "now if you a 3 million of elements to this OrderedCollection, you need to handle specifically”. What the VM does exactly in that case?
Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. On Nov 25, 2013, at 1:46 PM, Clément Bera <bera.clem...@gmail.com> wrote: > Hello, > > To answer your question, V8 definitely supports memory segments. I don't know > about papers but in the code each segment is an instance of Heap (see heap.cc > and heap.h in the source). The 2 young spaces are in another contiguous > segment of 8Mb. > > Each segment of V8 are one of this kind (all instances of Heap): > > * NewSpace: New object allocations go here. Capacity is 8MB. It's divided > into two contiguous semispaces, and periodically collected using Cheney's > algorithm. Uses bump-allocation. > * OldSpaces: These allocate memory in 64-128KB chunks of 8KB pages. They > come in the following flavors: > * MapSpace: Exclusively for Maps (similar to js::Shape), and Maps > *always* go here. > * CodeSpace: Exclusively for Code. > * DataSpace: For flat strings and numbers; can't reference objects, > except for maps. > * PointerSpace: For anything not a Map or Code that can reference other > objects. > * CellSpace: Seems to store global properties or something. > * LOSpace: For large objects, where "large" means it needs more than ~8KB > of storage. > > > I have no proof for hotspot (their code is too complex) but I'm sure they > have it too. > > For the other question (adding elements to OrderedCollection), Eliot will > answer it in more details, but the main idea is that you have the heap > chopped into segments of a fixed size (1Mb in Cog, and 64-128KB chunks in > V8), therefore for object bigger than a segment, you need to handle > specifically the object, i.e. having a segment of the size of the object. If > you add 30 000 elements to an OrderedCollection, the object will still be > under 1MB so it is ok, now if you a 3 million of elements to this > OrderedCollection, you need to handle specifically, Therefore you have > performance loss for object of more than 1Mb but there are not common so you > will not notice it (you can hardly have thousands of objects bigger than 1Mb > allocated and deallocated regularly, and you need this amount to notice the > performance loss). > > An interesting point in V8 is that the data and pointers are not in the same > spaces. It would mean in Cog, if I understand correctly, that byte and word > objects are not in the same space as other objects. I guess this simplifies > the GC logic. I don't know if they did that in VW. > > > 2013/11/25 Alexandre Bergel <alexandre.ber...@me.com> > Hi Eliot, > > I have a question still on segmented memory. > > Consider an object “c := OrderedCollection new”. It is likely that the > internal "array” and the object c will be in the same generation and in the > same memory segment. > If I add, let’s say, 30 000 000 elements into c. After the addition the array > will be very very big. Which means that it may be in a different segment > memory than the one that contains “c”. Do you feel this may be a problem? I > am thinking about a long jump between c and array. Long jumps cost more than > short jumps right? > > Do you feel there are some suboptimal situation with this situation? > > Alexandre > > NB: I cc the mailing list to see whether other may help in understand better > what’s going on with segment and generations > -- > _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: > Alexandre Bergel http://www.bergel.eu > ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. > > > > On Nov 19, 2013, at 1:37 PM, Eliot Miranda <eliot.mira...@gmail.com> wrote: > > > Hi Alexandre, > > > > > > On Mon, Nov 18, 2013 at 7:40 AM, Alexandre Bergel <alexandre.ber...@me.com> > > wrote: > > Hi Eliot, > > > > Stef told me you are working hard on improving the Pharo VM. > > In particular making the VM support fragmented memory. If I understand > > correctly, this will relieve the VM from having a continuous block of > > memory to hold the whole image. Really cool! > > > > A better term is segmented memory. fragmentation in memory management > > means free space getting divided into too small pieces to be useful. > > > > I have a general question regarding VM. Are you aware of other Virtual > > machines supporting this? Does the Java VM support fragmented memory? .Net? > > V8? > > > > Any VM that uses the train algorithm supports segmented memory. Any VM > > that uses "pools" or "regions" uses segmented memory. VisualWorks' VM > > supports segments. I'm pretty sure that V8 .Net & HotSpot provide > > segmented memory. > > > > > > I would like to mention this in a research paper I am working on. > > > > Cheers, > > Alexandre > > -- > > _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: > > Alexandre Bergel http://www.bergel.eu > > ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. > > > > > > > > > > > > > > -- > > best, > > Eliot > > >
