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From "Peter Edworthy" <pe...@edworthy.org>
Subject Re: [Arch] Class unloading and VM objects reclaim
Date Tue, 13 Sep 2005 13:52:22 GMT
Hello,

> It is useful to be able to specify certain characteristics of the
> virtual memory regions, eg that the nursery is at higher addresses,
> because the efficiency of the read and write barriers depends on being
> able to quickly identify nursery objects, and having the nursery in high
> addresses means you can do that with a single comparison.  Other
> barriers have other requirements.
>
> Is this what you mean by "the OS will be used to assign separate memory
> areas to separate pieces of the JVM" ?  In which case, I'd argue that
> it's highly desirable.

Actually I'd not thought of that use, I was imagining using the OS for
access checks. i.e. the VM is in one section, the VM/ClassLib interface in
another and the ClassLib in a final section. The OS could then screen
calls between sections based on a security policy handled at the OS level,
possibly via different 'users' for each memory section.

This could also be implemented in the VM though as fast address range
checks, owing to the coherent address space virtual memory can provide.

Thanks in advance,
Pete


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