Le 12/03/2012 01:44, Alex Rønne Petersen a écrit :
On 12-03-2012 01:41, bearophile wrote:
A significant percentage of heap memory in a 64 bit JavaVM is used by
references, that are 8 bytes long. To reduce this problem they have
invented "compressed references" (useful only for 64 bit systems),
that turn references to 32 bit again:
https://blogs.oracle.com/jrockit/entry/understanding_compressed_refer
ftp://public.dhe.ibm.com/software/webserver/appserv/was/WAS_V7_64-bit_performance.pdf
With them the total amount of heap memory decreases. They don't slow
down the class usage significantly, and the memory reduction reduces
the CPU cache pressure, increasing the performance a bit.
Will this idea be useful for 64 bit D/DMD too, for D GC-managed class
references (not for raw pointers)?
Bye,
bearophile
This probably can't work for D.
The problem is that D allows casting references to pointers. As we all
know, a pointer is a distinct type from a reference, and casting a
pointer to e.g. an integer type is perfectly valid and sometimes
necessary. So, that is to say, this would blow up when doing the
reference -> pointer conversion.
You could do it such that when one does the ref -> ptr conversion, the
reference is simply expanded to a normal pointer, and vice versa.
However, I'm not sure if this will hold water in the long run.
Additionally, 64bits pointer is good for us :
http://www.deadalnix.me/2012/03/05/impact-of-64bits-vs-32bits-when-using-non-precise-gc/
(shameless autopromotion inside).
