Nadav Har'El wrote:
On Tue, Jan 16, 2007, Rollo du Pre wrote about "Re: Websphere and Dark Matter":
I was hoping it would, yes. Does websphere not release memory back to
the OS when it not longer needs it? I'm concerned that if the memory
spiked for some reason (indexing a large document) then that would
hamper the rest of the OS because it'd hold on to far more memory than
is needed.
This is a well known, may I say infamous, Java issue. Java could, in theory,
easily shrink its heap as soon as it needs less memory, because in Java's GC
model, memory can be moved around so fragmentation is not a problem. But
unfortunately, the JVM's heap rarely does shrink by default: once the JVM's
heap grows, it rarely ever shrinks back.
Are you implying that the process memory shrinks, that memory is
returned to the kernel? I didn't read the page you referenced that way.
I know that if I allocate memory by memory mapping anonymous regions
with Linux/Unix I can give it back, but is that the technique that JVMs use?
It's not generally a problem though. Provided you have a compacting
garbage collector (and the Sun Java GC is one) then the unused memory
will just get paged out. It may be a different story on windows and it's
certainly a different story on an embedded platform, but releasing
memory to the kernel under Linux is not generally necessary or desirable.
jch
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