RE: Why separate pools?

[Alexei Pytel <pytel@xxxxxxxxxx>]

Single level storage means that all obejcts reside in a single virtual 
address space and every byte of every object on system has one unique 
address - in virtual memory.
One virtual address can have at most one real address - none if this page 
was not brought into real storage, exactly one if it was brought in.


    Alexei Pytel
always speaking for myself only




"Joe Pluta" <joepluta@xxxxxxxxxxxxxxxxx> 
Sent by: midrange-l-bounces@xxxxxxxxxxxx
11/23/2004 05:10 PM
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RE: Why separate pools?






Not to me.  When an object is read into memory, it by definition resides
in two places at one time, no?

There is a clear difference between virtual memory (the huge address
space that single level store inhabits) and physical memory.  There is a
map that indicates where on disk a given virtual address space resides,
and that's what the single-level store is about.

Then there's the paging mechanism, which tells you whether a copy of the
object already resides in physical memory.  Here, there is a difference
depending on whether the object is read-only or update-capable.  I could
see a problem if the object was write-capable and in two locations, but
it seems to me that a program object is not write capable (that's why
programs get "moved" to QRPLOBJ when you compile new versions).

Anyway, we're probably guessing and you're just as likely to be right as
I am.  Like I said, maybe someone from IBM can enlighten us.

Joe

> From: CWilt@xxxxxxxxxxxx
> 
> I don't know for sure, but....
> 
> It would seem that having "copies" of the object in multiple pools
would
> violate the whole idea of single level store.  I.E. the object exists
only
> in one place at a time.

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