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From Egor Pasko <egor.pa...@gmail.com>
Subject Re: [General VM] GC strategy:how to garbage collect short-lived objects quickly.
Date Thu, 14 Sep 2006 05:30:49 GMT
On the 0x1E4 day of Apache Harmony Leo Li wrote:
> Hi,all:
>     As we all know, java objects are allocated on heap instead of stack,
> thus there is a problem about how to garbage collect short-lived objects
> quickly.
>     In a recent real project I involved, a server built on java tries to
> send thousands of messages to client per second. A lot of short-lived
> messages is created as objects and discarded. (Although I can recycle these
> memory, there is still a byte array created during per call of nio read and
> write.) Since current GC strategy adopted by current RI starts to work only
> when the memory allocated approaching the limit of java heap, the work of GC
> is huge and will raise a wave on the server performance. Furthermore, after
> a long run, although I know GC will merge memory, the operating system
> reports there is memory fragment and in the worst case the OS will even
> report real memory is exhausted.
>     Of course it is possible to limit the java heap so as to force gc
> frequently as a workround, is it preferrable to collect short-lived objects
> quickly such as adopt aged-related object queues as one of the gc strategy?

what about forcing gc by hand? does it help?

>    What about the VMs here, drlvm or J9?

In a DRLVM JIT (Jitrino.OPT) there is an escape analysis prototype. It
detects objects that can be allocated on stack (and, hence, on
registers). Currently, it is switched off by default, and, when
enabled, it just marks the objects that are not escaped. This info is
never used in Jitrino.OPT yet. Sometimes, escape analyzers help, but
not very much :)

DRLVM GC gurus will say more ;)

Egor Pasko, Intel Managed Runtime Division

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