> From: Kevin P. Lawton [mailto:[EMAIL PROTECTED]]
<snip>
> > >// Attributes which change dynamically, depending on the
> > >// code that is running at the time.
> > >#define GuestPageData 0x0010 // Has been
> accessed with R/W
> > >#define GuestPageCode 0x0020 // Has associated
> prescanned code
> > >#define GuestPageHostSwapEligible 0x0040 // Page marked so
> host can swap
> > >#define GuestPagePDir 0x0080 // Contains Page Directory
> > >#define GuestPagePTbl 0x0100 // Contains a Page Table
> > >#define GuestPageIDT 0x0200 // Contains current IDT
> > >#define GuestPageGDT 0x0400 // Contains current GDT
> > >#define GuestPageLDT 0x0800 // Contains current LDT
> > >#define GuestPageTSS 0x1000 // Contains current TSS
> > >
> >
> > Are all of these really non-exclusive? Or are there
> mutually exclusive
> > alternatives here that could be capitalised upon to reduce
> bit usage,
> > because you're already running close to the limits of 16
> bits, and you
> > don't want to double the memory usage up to 32 bits.
>
> They are exclusive enough, I'd like to leave them this way.
> There are 4 more bits left. For 64MB of guest mem, this would
> consume a wapping 32K of memory @ 16bit quantities.
<snip>
Perhaps I missed something in the reading, but Kevin said, "They are
exclusive enough". Which I would agree with looking at names of the defines.
However, I think the point was that the values used are not exclusive,
rather in their current form they may be or'd together to form combinations.
I don't think a page can be GuestPageGDT|GuestPageLDT. If I understand
properly, what Jullian was getting at was that some of these could be
changed like this:
// Attributes which change dynamically, depending on the
// code that is running at the time.
#define GuestPageData 0x0010 // Has been accessed with R/W
#define GuestPageCode 0x0020 // Has associated prescanned code
#define GuestPageHostSwapEligible 0x0040 // Page marked so host can swap
#define GuestPagePDir 0x0080 // Contains Page Directory
#define GuestPagePTbl 0x0100 // Contains a Page Table
#define GuestPageIDT 0x0180 // Contains current IDT
#define GuestPageGDT 0x0200 // Contains current GDT
#define GuestPageLDT 0x0280 // Contains current LDT
#define GuestPageTSS 0x0300 // Contains current TSS
#define GuestPageContentMask 0x0380 // Mask for checking page
contents
This alone would leave us 6 bits instead of 4.
