Subject: Re: uvm_km_valloc_align() and USPACE (Re: CVS commit: syssrc)
To: None <,>
From: Chris Torek <torek@BSDI.COM>
List: tech-kern
Date: 12/02/2000 22:47:30
>Umm.. NBPG was constant but PAGE_SIZE was not?
>Or NBPG was a hardware value and PAGE_SIZE was for vm?

The latter.  This was all clearer in the 4.[123]BSD system before
the Mach VM went in:

	NBPG:	hardware page size in bytes
	CLSIZE: "cluster" size for making bigger VM pages out of
		small hardware pages

I forget whether PGOFSET was NBPG-1 or CLBYTES-1, though.  CLSIZE
was 2 (on the VAX) so that the OS could pretend the hardware had
1024-byte pages, and reduce the paging overhead.

On the Tahoe, 68020, and other "post-4.3BSD" non-VAX ports, CLSIZE
was effectively always 1.